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Metals, Volume 8, Issue 1 (January 2018)

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Cover Story (view full-size image) The formation of Mn–C short-range ordering (SRO) during recrystallization of an X60Mn18 steel was [...] Read more.
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Editorial

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Open AccessEditorial Acknowledgement to Reviewers of Metals in 2017
Metals 2018, 8(1), 46; https://doi.org/10.3390/met8010046
Received: 10 January 2018 / Revised: 10 January 2018 / Accepted: 10 January 2018 / Published: 12 January 2018
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Abstract
Peer review is an essential part in the publication process, ensuring that Metals maintains high quality standards for its published papers[...] Full article

Research

Jump to: Editorial, Review

Open AccessArticle The α → ω Transformation in Titanium-Cobalt Alloys under High-Pressure Torsion
Received: 10 November 2017 / Revised: 10 December 2017 / Accepted: 18 December 2017 / Published: 21 December 2017
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Abstract
The pressure influence on the α → ω transformation in Ti–Co alloys has been studied during high pressure torsion (HPT). The α → ω allotropic transformation takes place at high pressures in titanium, zirconium and hafnium as well as in their alloys. The
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The pressure influence on the α → ω transformation in Ti–Co alloys has been studied during high pressure torsion (HPT). The α → ω allotropic transformation takes place at high pressures in titanium, zirconium and hafnium as well as in their alloys. The transition pressure, the ability of high pressure ω-phase to retain after pressure release, and the pressure interval where α and ω phases coexist depend on the conditions of high-pressure treatment. During HPT in Bridgeman anvils, the high pressure is combined with shear strain. The presence of shear strain as well as Co addition to Ti decreases the onset of the α → ω transition from 10.5 GPa (under quasi-hydrostatic conditions) to about 3.5 GPa. The portion of ω-phase after HPT at 7 GPa increases in the following sequence: pure Ti → Ti–2 wt % Co → Ti–4 wt % Co → Ti–4 wt % Fe. Full article
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Open AccessArticle Magnetic Investigations of Steel Degradation Using a Magnetic Hysteresis Scaling Technique
Received: 11 November 2017 / Revised: 16 December 2017 / Accepted: 19 December 2017 / Published: 21 December 2017
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Abstract
We report the results of magnetic measurements on austenitic stainless steels and duplex stainless steels using a magnetic hysteresis scaling technique. Unlike saturation hysteresis loops, this scaling technique, which uses a set of minor hysteresis loops, can be used in low measurement fields.
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We report the results of magnetic measurements on austenitic stainless steels and duplex stainless steels using a magnetic hysteresis scaling technique. Unlike saturation hysteresis loops, this scaling technique, which uses a set of minor hysteresis loops, can be used in low measurement fields. We show that there is a universal scaling power law between minor-loop parameters, which is independent from the level of deformation. The behavior of a coefficient deduced from the scaling law was explained from the viewpoint of the morphology of a ferromagnetic phase. Full article
(This article belongs to the Special Issue Advanced Non-Destructive Testing in Steels)
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Open AccessArticle Microstructure Evolution and Microstructural Characteristics of Al–Mg–Si Aluminum Alloys Fabricated by a Modified Strain-Induced Melting Activation Process
Received: 14 November 2017 / Revised: 18 December 2017 / Accepted: 19 December 2017 / Published: 22 December 2017
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Abstract
A modified strain-induced melting activation (SIMA) process is shown to improve high-temperature formability. The microstructural characteristics of the spheroidized grains of SIMA-processed alloys affect high-temperature formability. The effects of hot extrusion parameters and chemical composition on the evolution of spheroidized grains were investigated
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A modified strain-induced melting activation (SIMA) process is shown to improve high-temperature formability. The microstructural characteristics of the spheroidized grains of SIMA-processed alloys affect high-temperature formability. The effects of hot extrusion parameters and chemical composition on the evolution of spheroidized grains were investigated using several 6xxx series aluminum alloys subjected to a modified SIMA process. The results show that 6066 aluminum alloy is the most suitable alloy for the SIMA process, as it contains sufficient Mg, Si, Cu, and Mn. Adequate amounts of Mg, Si, and Cu lead to a high liquid fraction, and a sufficient addition of Mn inhibits grain growth. Proper hot extrusion parameters are essential, because initial fine and uniform recrystallized grains lead to fine and uniform globules. The phases at the global grain boundaries of 6066 aluminum alloy are eutectic phases of Al and Si, Al and Mg2Si, and Al and Al2Cu, as analyzed using transmission electron microscopy. Full article
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Open AccessArticle Dependence of Creep Performance and Microstructure Evolution on Solution Cooling Rate in a Polycrystalline Superalloy
Received: 30 November 2017 / Revised: 16 December 2017 / Accepted: 19 December 2017 / Published: 22 December 2017
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Abstract
It is well known that the solution cooling rate has a great effect on the creep life of superalloys. In this research, three typical cooling rates were applied to generate different distributions of γ’ precipitates for creep tests. Ingots used to make specimens
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It is well known that the solution cooling rate has a great effect on the creep life of superalloys. In this research, three typical cooling rates were applied to generate different distributions of γ’ precipitates for creep tests. Ingots used to make specimens were manufactured by hot extrusion, and the master alloy had the composition of an FGH4096 power metallurgy superalloy. SEM and SESD were used to observe the microstructure’s evolution. The experimental results show that the fastest cooling rate corresponds to the highest creep life as well as the smallest rupture strain, and vice versa. The microscopic observations disclose that with an increasing cooling rate, the size and area fraction of γ’ precipitates decrease, and the rupture mechanism changes from transgranular to intergranular. Moreover, some γ’ precipitates changed to cuboid after the creep test. The results will provide new technological processes to design more creep-resistant, nickel-base superalloys. Full article
(This article belongs to the Special Issue Advanced Mechanical Testing of Powder Metallurgy Alloys)
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Open AccessArticle Development of Amplifier Circuit by Active-Dummy Method for Atmospheric Corrosion Monitoring in Steel Based on Strain Measurement
Received: 31 October 2017 / Revised: 14 December 2017 / Accepted: 18 December 2017 / Published: 22 December 2017
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Abstract
This paper describes an amplifier circuit fabricated by the active-dummy method for atmospheric corrosion monitoring based on strain measurement. The circuit was used to determine the relationship between the voltage and strain. Experiments involving the thickness reduction of low-carbon steel test pieces induced
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This paper describes an amplifier circuit fabricated by the active-dummy method for atmospheric corrosion monitoring based on strain measurement. The circuit was used to determine the relationship between the voltage and strain. Experiments involving the thickness reduction of low-carbon steel test pieces induced by galvanostatic electrolysis were carried out with the amplifier circuit. The circuit was capable of accurately measuring signals induced by the thickness reduction of the test piece. Moreover, the circuit was assessed for the effects of environmental temperature drift, and was found to exhibit a high tolerance. The proposed amplifier circuit would be suitable for atmospheric corrosion monitoring in many types of infrastructure. Full article
(This article belongs to the Special Issue Advanced Non-Destructive Testing in Steels)
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Open AccessArticle Fracture Toughness Prediction under Compressive Residual Stress by Using a Stress-Distribution T-Scaling Method
Received: 23 November 2017 / Revised: 20 December 2017 / Accepted: 20 December 2017 / Published: 25 December 2017
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Abstract
The improvement in the fracture toughness Jc of a material in the ductile-to-brittle transition temperature region due to compressive residual stress (CRS) was considered in this study. A straightforward fracture prediction was performed for a specimen with mechanical CRS by using the
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The improvement in the fracture toughness Jc of a material in the ductile-to-brittle transition temperature region due to compressive residual stress (CRS) was considered in this study. A straightforward fracture prediction was performed for a specimen with mechanical CRS by using the T-scaling method, which was originally proposed to scale the fracture stress distributions between different temperatures. The method was validated for a 780-MPa-class high-strength steel and 0.45% carbon steel. The results showed that the scaled stress distributions at fracture loads without and with CRS are the same, and that Jc improvement was caused by the loss in the one-to-one correspondence between J and the crack-tip stress distribution. The proposed method is advantageous in possibly predicting fracture loads for specimens with CRS by using only the stress–strain relationship, and by performing elastic-plastic finite element analysis, i.e., without performing fracture toughness testing on specimens without CRS. Full article
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Open AccessArticle Optimization of Processing Parameters for a Reverse Drawing–Flanging Combined Process for a B550CL High-Strength Steel Spoke Based on Grey Relational Analysis
Received: 13 November 2017 / Revised: 20 December 2017 / Accepted: 21 December 2017 / Published: 26 December 2017
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Abstract
Undesired wall thickness distribution and flanging cracking easily occur in reverse drawing–flanging combined processes of steel spokes when improper process parameters are used. Thus, based on GRA (grey relational analysis) and FEM (finite element method), a GRA model for a reverse drawing–flanging combined
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Undesired wall thickness distribution and flanging cracking easily occur in reverse drawing–flanging combined processes of steel spokes when improper process parameters are used. Thus, based on GRA (grey relational analysis) and FEM (finite element method), a GRA model for a reverse drawing–flanging combined process for high strength steel B550CL spoke was established and validated. The results show that: (1) the most significant factors affecting uneven wall thickness distribution and excessive thinning in the mounting zone and center hole cracking are the friction coefficient and the shape of punch, respectively; (2) the non-uniformity of wall thickness U increases with the increase of the friction coefficient. The conical punch has a lower thinning ratio T, the spherical punch has a lower value of damage D; (3) considering synthetically the indexes of uneven wall thickness distribution, the excessive thinning in the mounting zone and center hole cracking, optimal results for the process parameters are obtained. Full article
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Open AccessArticle Recovery of Iron from Pyrolusite Leaching Slag by a Lab-Scale Circulation Process of Oxalic Acid Leaching and Ultraviolet Irradiation
Received: 11 November 2017 / Revised: 18 December 2017 / Accepted: 21 December 2017 / Published: 26 December 2017
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Abstract
Pyrolusite leaching slag is a Fe-containing slag generated from pyrolusite leaching process with SO2. Recovery of iron from the slag not only has economic benefit, but also prevents the secondary pollution to the environment. A novel lab-scale cyclic process for recovering
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Pyrolusite leaching slag is a Fe-containing slag generated from pyrolusite leaching process with SO2. Recovery of iron from the slag not only has economic benefit, but also prevents the secondary pollution to the environment. A novel lab-scale cyclic process for recovering iron from pyrolusite leaching slag was introduced. The process contains two steps: (1) iron was leached with oxalic acid and [Fe(C2O4)n](3−2n)+ solution was generated; (2) the [Fe(C2O4)n](3−2n)+ solution was irradiated by ultraviolet and ferrous oxalate precipitation were obtained. The effect of operation parameter on leaching and irradiation process were studied separately. In the leaching process, the optimal solid/liquid ratio, oxalic acid concentration, leaching temperature, stirring rate, and leaching time are 1:50, 0.40 mol/L, 95 °C, 300 r/min, and 3 h, respectively. In the irradiation process, the best irradiation wavelength, Fe/oxalic acid molar ratio and irradiation time are 254 nm, 1:4, and 30 min. Besides, a test of 9 continuous cycles was carried out and the performance and material balance of the combined process were investigated. The results showed that the cyclic process is entirely feasible and prove to be stable producing, and ferrous oxalate of 99.32% purity. Material balance indicated that 95.17% of iron was recovered in the form of FeC2O4·2H2O, and the recovery efficiency of oxalic acid was 58.52%. Full article
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Open AccessFeature PaperArticle A Unified Physical Model for Creep and Hot Working of Al-Mg Solid Solution Alloys
Received: 27 November 2017 / Revised: 19 December 2017 / Accepted: 22 December 2017 / Published: 27 December 2017
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Abstract
The description of the dependence of steady-state creep rate on applied stress and temperature is almost invariably based on the Norton equation or on derived power-law relationships. In hot working, the Norton equation does not work, and is therefore usually replaced with the
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The description of the dependence of steady-state creep rate on applied stress and temperature is almost invariably based on the Norton equation or on derived power-law relationships. In hot working, the Norton equation does not work, and is therefore usually replaced with the Garofalo (sinh) equation. Both of these equations are phenomenological in nature and can be seldom unambiguously related to microstructural parameters, such as dislocation density, although early efforts in this sense led to the introduction of the “natural power law” with exponent 3. In an attempt to overcome this deficiency, a recent model with sound physical basis has been successfully used to describe the creep response of fcc metals, such as copper. The main advantage of this model is that it does not require any data fitting to predict the strain rate dependence on applied stress and temperature, which is a particularly attractive peculiarity when studying the hot workability of metals. Thus, the model, properly modified to take into account solid solution strengthening effects, has been here applied to the study of the creep and hot-working of simple Al-Mg single phase alloys. The model demonstrated an excellent accuracy in describing both creep and hot working regimes, still maintaining its most important feature, that is, it does not require any fitting of the experimental data. Full article
(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)
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Open AccessArticle Analysis of the Microstructure and Selected Properties of the Aluminium Alloys Used in Automotive Air-Conditioning Systems
Metals 2018, 8(1), 10; https://doi.org/10.3390/met8010010
Received: 6 December 2017 / Revised: 22 December 2017 / Accepted: 22 December 2017 / Published: 28 December 2017
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Abstract
The results of microstructure examinations and studies of selected mechanical properties of four aluminium alloys used in the production of automotive air-conditioning ducts (AA3103, AA5049, AA6060, AA6063) before and after the ASTM G85:A3 SWAAT Test (Sea Water Acetic Acid Test) for corrosion resistance
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The results of microstructure examinations and studies of selected mechanical properties of four aluminium alloys used in the production of automotive air-conditioning ducts (AA3103, AA5049, AA6060, AA6063) before and after the ASTM G85:A3 SWAAT Test (Sea Water Acetic Acid Test) for corrosion resistance are presented. Materials used for the manufacture of such components should be temperature stable, and therefore thermal resistance tests were carried out in a wide range of temperatures, i.e., −25 °C, 25 °C, 40 °C, 60 °C, 80 °C, 100 °C, 140 °C, 180 °C, and 220 °C. Annealing was performed for 72 h and 240 h, followed by cooling in water. The obtained results have proved that the non-precipitation-hardenable AA3103 and AA5049 alloys remain stable in the entire range of the investigated temperatures. The measured microhardness of these alloys was 43–46 HV0.1 for AA3103 and 56–64 HV0.1 for AA5049. The microhardness of the 6xxx series aluminium alloys was not stable in the investigated range of temperatures. The maximum was observed in the temperature range of 100–140 °C, which corresponded to the precipitation process of intermetallic phases, as further confirmed by microstructure observations. After the corrosion test, the mechanical properties and elongation decreased by about 5–20%. Full article
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Open AccessArticle Strain Rate Effect on Tensile Behavior for a High Specific Strength Steel: From Quasi-Static to Intermediate Strain Rates
Metals 2018, 8(1), 11; https://doi.org/10.3390/met8010011
Received: 6 December 2017 / Revised: 26 December 2017 / Accepted: 27 December 2017 / Published: 29 December 2017
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Abstract
The strain rate effect on the tensile behaviors of a high specific strength steel (HSSS) with dual-phase microstructure has been investigated. The yield strength, the ultimate strength and the tensile toughness were all observed to increase with increasing strain rates at the range
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The strain rate effect on the tensile behaviors of a high specific strength steel (HSSS) with dual-phase microstructure has been investigated. The yield strength, the ultimate strength and the tensile toughness were all observed to increase with increasing strain rates at the range of 0.0006 to 56/s, rendering this HSSS as an excellent candidate for an energy absorber in the automobile industry, since vehicle crushing often happens at intermediate strain rates. Back stress hardening has been found to play an important role for this HSSS due to load transfer and strain partitioning between two phases, and a higher strain rate could cause even higher strain partitioning in the softer austenite grains, delaying the deformation instability. Deformation twins are observed in the austenite grains at all strain rates to facilitate the uniform tensile deformation. The B2 phase (FeAl intermetallic compound) is less deformable at higher strain rates, resulting in easier brittle fracture in B2 particles, smaller dimple size and a higher density of phase interfaces in final fracture surfaces. Thus, more energy need be consumed during the final fracture for the experiments conducted at higher strain rates, resulting in better tensile toughness. Full article
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Open AccessArticle Electrolytic Plasma Polishing of Pipe Inner Surfaces
Metals 2018, 8(1), 12; https://doi.org/10.3390/met8010012
Received: 7 November 2017 / Revised: 21 December 2017 / Accepted: 23 December 2017 / Published: 29 December 2017
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Abstract
Smooth surfaces are becoming increasingly important in many industries, such as medical, chemical or food. In some industrial areas, the mechanical treatment of surfaces (grinding and polishing) does not fulfil desired specifications. Non-abrasive methods (chemical and electrochemical) have the advantage that even complex
[...] Read more.
Smooth surfaces are becoming increasingly important in many industries, such as medical, chemical or food. In some industrial areas, the mechanical treatment of surfaces (grinding and polishing) does not fulfil desired specifications. Non-abrasive methods (chemical and electrochemical) have the advantage that even complex geometries and free-form shapes can be polished. In the context of this paper, electrochemical surface treatment is considered in more detail. Both electro polishing, which is state of the art, and the novel electrolytic plasma polishing (EPP) process are presented. This paper focusses on the electrolytic plasma polishing because it has many advantages compared to the process of electro polishing. The theoretical operation of the electrolytic plasma polishing is shown. A prototype system for plasma polishing of internal surfaces of pipes was installed and a polishing head was developed. Several parameters are investigated, such as the width of the adjustable polishing head gap and different velocities v or different applied potential differences U, and first results of the average surface roughness Sa as function of the various parameters were evaluated. It can be seen that a stable polishing process can be achieved at the highest potential difference of 320 V and that the average surface roughness Sa reaches a range from 0.065 to 0.090 µm. At the same time, it has been shown that with increasing potential difference, the average surface roughness becomes independent of the width of the adjustable polishing head gap. Full article
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Open AccessArticle Dry Sliding Tribological Behavior of TC11 Titanium Alloy Subjected to the Ultrasonic Impacting and Rolling Process
Metals 2018, 8(1), 13; https://doi.org/10.3390/met8010013
Received: 27 October 2017 / Revised: 15 December 2017 / Accepted: 15 December 2017 / Published: 29 December 2017
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Abstract
The dry sliding friction and wear behaviors of TC11 titanium alloy subjected to the ultrasonic impacting and rolling process (UIRP) were studied in the present work. The microstructure of the deformation layer and the morphology of the worn surfaces were observed. The results
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The dry sliding friction and wear behaviors of TC11 titanium alloy subjected to the ultrasonic impacting and rolling process (UIRP) were studied in the present work. The microstructure of the deformation layer and the morphology of the worn surfaces were observed. The results clearly show that the wear performance of TC11 alloy after UIRP is better than that of TC11 alloy before UIRP under the same testing conditions. This can be attributed to the gradient nanostructure, work hardening, and low surface roughness of the treated surface layer. For the untreated samples, wear resistance first decreases and then increases with the increase of the sliding speed. Both the friction coefficient (FC) and wear rate reach a maximum value at a sliding speed of 478 r/min, and the corresponding worn surface is the most serious. While for UIRP treated samples, better friction and wear behaviors are obtained at a sliding speed of 478 r/min. This is because the deformation layer plays a protective role against wear. Full article
(This article belongs to the Special Issue Kinetic Surface Treatments)
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Open AccessArticle Nondestructive Evaluation of Strain-Induced Phase Transformation and Damage Accumulation in Austenitic Stainless Steel Subjected to Cyclic Loading
Metals 2018, 8(1), 14; https://doi.org/10.3390/met8010014
Received: 24 October 2017 / Revised: 19 December 2017 / Accepted: 27 December 2017 / Published: 29 December 2017
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Abstract
Strain-induced phase transformation and damage accumulation in austenitic stainless steel subjected to cyclic loading were investigated by nondestructive evaluation. The cyclic loading test was performed at various strain amplitudes at the same strain rate. The volume fraction of the strain-induced phase transformation (α′-martensite)
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Strain-induced phase transformation and damage accumulation in austenitic stainless steel subjected to cyclic loading were investigated by nondestructive evaluation. The cyclic loading test was performed at various strain amplitudes at the same strain rate. The volume fraction of the strain-induced phase transformation (α′-martensite) was determined by ferrite scope and magnetic coercivity measurement. The damage accumulation and microstructure of cyclic loading specimens were characterized by microstructural observation. The cyclic hardening and cyclic softening behavior are discussed in terms of the generation of strain-induced martensite phases and a dislocation substructure at each strain amplitude. The volume fraction of the strain-induced phase increased with the strain amplitude. The increase in α′-martensite was evaluated by measuring the ultrasonic nonlinearity parameter. The presence of α′-martensite is sufficient to distort the austenitic matrix due to an interface misfit between the austenite matrix and α′-martensite, resulting in wave distortion of the longitudinal wave. From this wave distortion, super-harmonics may be generated with nucleation of the strain-induced martensite, a process that strongly depends on the strain amplitude. Full article
(This article belongs to the Special Issue Advanced Non-Destructive Testing in Steels)
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Open AccessArticle On Sluggish Diffusion in Fcc Al–Co–Cr–Fe–Ni High-Entropy Alloys: An Experimental and Numerical Study
Metals 2018, 8(1), 16; https://doi.org/10.3390/met8010016
Received: 5 December 2017 / Revised: 22 December 2017 / Accepted: 25 December 2017 / Published: 30 December 2017
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Abstract
High-throughput measurement using the numerical inverse method combined with the diffusion multiple technique was employed to determine the composition-dependent interdiffusion coefficients in fcc Al–Co–Cr–Fe–Ni high-entropy alloys at 1273, 1323, and 1373 K. The reliability of the obtained interdiffusion coefficients was confirmed by comparing
[...] Read more.
High-throughput measurement using the numerical inverse method combined with the diffusion multiple technique was employed to determine the composition-dependent interdiffusion coefficients in fcc Al–Co–Cr–Fe–Ni high-entropy alloys at 1273, 1323, and 1373 K. The reliability of the obtained interdiffusion coefficients was confirmed by comparing the model-predicted composition/interdiffusion flux profiles with the experimental data. The tracer diffusivities of the components were then predicted based on the obtained interdiffusion coefficients and the simplified thermodynamic description. The diagonal interdiffusion coefficients in the present high-entropy alloys were comprehensively compared with those in conventional fcc alloys. Therefore, the sluggish diffusion effect does not apply for all the elements in the present fcc Al–Co–Cr–Fe–Ni high-entropy alloys. A similar result was also observed for the evaluated tracer diffusivities. Full article
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Open AccessCommunication Synthesis of Metastable Au-Fe Alloy Using Ordered Nanoporous Silica as a Hard Template
Metals 2018, 8(1), 17; https://doi.org/10.3390/met8010017
Received: 24 November 2017 / Revised: 22 December 2017 / Accepted: 23 December 2017 / Published: 30 December 2017
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Abstract
Nanoporous Au-Fe alloy was synthesized via a wet chemistry route using ordered nanoporous silica as a hard template. The nanoporous Au-Fe consisted of aligned arrays of nanopores that were uniform in composition and ordered in hexagonal lattice, whereas Au-Fe nanoparticles synthesized without templates
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Nanoporous Au-Fe alloy was synthesized via a wet chemistry route using ordered nanoporous silica as a hard template. The nanoporous Au-Fe consisted of aligned arrays of nanopores that were uniform in composition and ordered in hexagonal lattice, whereas Au-Fe nanoparticles synthesized without templates exhibited broad dispersions in the chemical composition and/or particle size. Nanoporous Au-Fe has potential for applications as catalysts and/or adsorbents because of the large specific surface area of 81.2 m2·g−1 and high pore volume of 0.56 cm3·g−1. Full article
(This article belongs to the Special Issue Nanoporous Metals)
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Open AccessArticle Effect of Constitutive Equations on Springback Prediction Accuracy in the TRIP1180 Cold Stamping
Metals 2018, 8(1), 18; https://doi.org/10.3390/met8010018
Received: 30 October 2017 / Revised: 21 November 2017 / Accepted: 25 December 2017 / Published: 30 December 2017
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Abstract
This study aimed to evaluate the effect of constitutive equations on springback prediction accuracy in cold stamping with various deformation modes. This study investigated the ability of two yield functions to describe the yield behavior: Hill’48 and Yld2000-2d. Isotropic and kinematic hardening models
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This study aimed to evaluate the effect of constitutive equations on springback prediction accuracy in cold stamping with various deformation modes. This study investigated the ability of two yield functions to describe the yield behavior: Hill’48 and Yld2000-2d. Isotropic and kinematic hardening models based on the Yoshida-Uemori model were adopted to describe the hardening behavior. The chord modulus model was used to calculate the degradation of the elastic modulus that occurred during plastic loading. Various material tests (such as uniaxial tension, tension-compression, loading-unloading, and hydraulic bulging tests) were conducted to determine the material parameters of the models. The parameters thus obtained were implemented in a springback prediction finite element (FE) simulation, and the results were compared to experimental data. The springback prediction accuracy was evaluated using U-bending and T-shape drawing. The constitutive equations wielded significant influence over the springback prediction accuracy. This demonstrates the importance of selecting appropriate constitutive equations that accurately describe the material behaviors in FE simulations. Full article
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
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Open AccessArticle Investigation of Structural-Phase States and Features of Plastic Deformation of the Austenitic Precipitation-Hardening Co-Ni-Nb Alloy
Metals 2018, 8(1), 19; https://doi.org/10.3390/met8010019
Received: 6 November 2017 / Revised: 11 December 2017 / Accepted: 23 December 2017 / Published: 30 December 2017
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Abstract
This article presents the results of investigation of the influence of holding temperature during the quenching process on the microstructure and superplasticity of the Co-Ni-Nb alloy. Temperature-strain rate intervals of the deformation of the superplasticity effects are stated. The optimal regimes of the
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This article presents the results of investigation of the influence of holding temperature during the quenching process on the microstructure and superplasticity of the Co-Ni-Nb alloy. Temperature-strain rate intervals of the deformation of the superplasticity effects are stated. The optimal regimes of the preliminary treatment by quenching and rolling as well as the routine of the superplastic deformation of the Co-Ni-Nb alloy are defined. The interval of the temperatures of the precipitation, morphology, composition, type and parameters of the lattice of the secondary phase, which appears after the annealing + rolling (to 90%) Co-Ni-Nb alloy, are determined. Full article
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Open AccessArticle Corrosion Fatigue of Fine Grain Mg-Zn-Zr and Mg-Y-Zn Alloys
Metals 2018, 8(1), 20; https://doi.org/10.3390/met8010020
Received: 29 November 2017 / Revised: 22 December 2017 / Accepted: 29 December 2017 / Published: 31 December 2017
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Abstract
Corrosion fatigue data for magnesium alloys are still scarce. The present communication reports the results of microstructural investigations and fatigue testing of the fine grain Mg-Zn-Zr (ZK60) alloy after multiaxial isothermal forging and of the hot extruded Mg-Y-Zn (WZ21) alloy in air and
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Corrosion fatigue data for magnesium alloys are still scarce. The present communication reports the results of microstructural investigations and fatigue testing of the fine grain Mg-Zn-Zr (ZK60) alloy after multiaxial isothermal forging and of the hot extruded Mg-Y-Zn (WZ21) alloy in air and in the 0.9% NaCl water solution. Both of the alloys demonstrate a very good high-cycle fatigue performance in air. However, the significant drop of fatigue resistance is observed in the corrosive environment. Results are discussed from perspectives of potential applications and future studies. Full article
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Open AccessArticle Welding Residual Stress Analysis and Fatigue Strength Assessment of Multi-Pass Dissimilar Material Welded Joint between Alloy 617 and 12Cr Steel
Metals 2018, 8(1), 21; https://doi.org/10.3390/met8010021
Received: 30 November 2017 / Revised: 26 December 2017 / Accepted: 27 December 2017 / Published: 31 December 2017
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Abstract
The reliability of welded structure can be evaluated through welding residual stress analysis and fatigue strength assessment. In this study, welding residual stresses of multi-pass dissimilar material welded joint between alloy 617 and 12Cr steel were analyzed numerically and experimentally. Fatigue strength was
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The reliability of welded structure can be evaluated through welding residual stress analysis and fatigue strength assessment. In this study, welding residual stresses of multi-pass dissimilar material welded joint between alloy 617 and 12Cr steel were analyzed numerically and experimentally. Fatigue strength was then assessed in the air. Based on results of welding residual stress analysis and fatigue strength assessment, a fatigue design method considering welding residual stress was investigated. Welding residual stresses at the weld of dissimilar welded joints distributed complicatedly on longitudinal and transverse directions, showing differences but a very similar distribution tendency between numerical and experimental results. Numerical and experimental peak values of welding residual stresses at HAZ of the weld on the 12Cr steel side were predicted to be 333 MPa and 282 MPa HAZ, respectively. The fatigue limit of dissimilar material welded joint between alloy 617 and 12Cr steel was assessed to be 306.8 MPa, which was 40% of tensile strength (767 MPa) of dissimilar material welded joint. However, the stress range including welding residual stress was assessed to be 206.9 MPa, which was 14% lower than that calculated by including the effect of residual stresses. Full article
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Open AccessArticle Local Buckling Behavior and Plastic Deformation Capacity of High-Strength Pipe at Strike-Slip Fault Crossing
Metals 2018, 8(1), 22; https://doi.org/10.3390/met8010022
Received: 17 November 2017 / Revised: 26 December 2017 / Accepted: 26 December 2017 / Published: 31 December 2017
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Abstract
As a typical hazard threat for buried pipelines, an active fault can induce large plastic deformation in a pipe, leading to rupture failure. The mechanical behavior of high-strength X80 pipeline subjected to strike-slip fault displacements was investigated in detail in the presented study
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As a typical hazard threat for buried pipelines, an active fault can induce large plastic deformation in a pipe, leading to rupture failure. The mechanical behavior of high-strength X80 pipeline subjected to strike-slip fault displacements was investigated in detail in the presented study with parametric analysis performed by the finite element model, which simulates pipe and soil constraints on pipe by shell and nonlinear spring elements respectively. Accuracy of the numerical model was validated by previous full-scale experimental results. Insight of local buckling response of high-strength pipe under compressive strike-slip fault was revealed. Effects of the pipe-fault intersection angle, pipe operation pressure, pipe wall thickness, soil parameters and pipe buried depth on critical section axial force in buckled area, critical fault displacement, critical compressive strain and post buckling response were elucidated comprehensively. In addition, feasibility of some common buckling failure criteria (i.e., the CSA Z662 model proposed by Canadian Standard association, the UOA model proposed by University of Alberta and the CRES-GB50470 model proposed by Center of Reliable Energy System) was discussed by comparing with numerical results. This study can be referenced for performance-based design and assessment of buried high-strength pipe in geo-hazard areas. Full article
(This article belongs to the Special Issue Mechanical Behavior of High-Strength Low-Alloy Steels)
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Open AccessArticle Choosing the Production Function Model for an Optimal Measurement of the Restructuring Efficiency of the Polish Metallurgical Sector in Years 2000–2015
Metals 2018, 8(1), 23; https://doi.org/10.3390/met8010023
Received: 15 December 2017 / Revised: 26 December 2017 / Accepted: 28 December 2017 / Published: 31 December 2017
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Abstract
Between 2000 and 2015, the Polish metallurgical sector was subject to serious restructuring. Presented research aimed at providing a framework for possibly most accurate measurement of efficiency of this process. The study employed: (I) Quantitative research for elaboration of production function models: power
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Between 2000 and 2015, the Polish metallurgical sector was subject to serious restructuring. Presented research aimed at providing a framework for possibly most accurate measurement of efficiency of this process. The study employed: (I) Quantitative research for elaboration of production function models: power regression Cobb-Douglas function with its developments; (II) Qualitative research: Analytic Hierarchy Process for assessment of relevance of efficiency evaluation criteria in reference to various production function models in metallurgy sector: (i) sectoral added value (net production); (ii) production sold; and, (iii) steel production volume. Criteria relevance has been assessed by scientists and practitioners with specialization in metallurgy. As a result the sectoral added value function has been chosen as the one that optimally reflects sector’s restructuring efficiency. This, in turn, constitutes a qualitative confirmation of previous research result, which has been verified with a quantitative method. Practical outcome is a more precise modelling of efficiency of restructuring processes in the metallurgical sector, both for scientific and business needs. The main research limitations originate from the sector itself—in order to make our tool more universal, further research should be led in parallel branches of industry. Full article
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Open AccessFeature PaperArticle Super Abrasive Machining of Integral Rotary Components Using Grinding Flank Tools
Metals 2018, 8(1), 24; https://doi.org/10.3390/met8010024
Received: 28 November 2017 / Revised: 28 December 2017 / Accepted: 29 December 2017 / Published: 1 January 2018
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Abstract
Manufacturing techniques that are applied to turbomachinery components represent a challenge in the aeronautic sector. These components require high resistant super-alloys in order to satisfy the extreme working conditions they have to support during their useful life. Besides, in the particular case of
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Manufacturing techniques that are applied to turbomachinery components represent a challenge in the aeronautic sector. These components require high resistant super-alloys in order to satisfy the extreme working conditions they have to support during their useful life. Besides, in the particular case of Integrally Bladed Rotors (IBR), usually present complex geometries that need to be roughed and finished by milling and grinding processes, respectively. In order to improve their manufacturing processes, Super Abrasive Machining (SAM) is presented as a solution because it combines the advantages of the use of grinding tools with milling feed rates. However, this innovative technique usually needed high tool rotary speed and pure cutting oils cooling. These issues implied that SAM technique was not feasible in conventional machining centers. In this work, these matters were tackled and the possibility of using SAM in these five-axis centers with emulsion coolants was achieved. To verify this approach, Inconel 718 single blades with non-ruled surfaces were manufactured with Flank-SAM technique and conventional milling process, analyzing cutting forces, surface roughness, and dimension accuracy in both cases. The results show that SAM implies a suitable, controllable, and predictable process to improve the manufacture of aeronautical critical components, such as IBR. Full article
(This article belongs to the Special Issue Machining and Finishing of Nickel and Titanium Alloys)
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Open AccessArticle Characteristics of Residual Stresses Generated by Induction Heating on Steel Plates
Metals 2018, 8(1), 25; https://doi.org/10.3390/met8010025
Received: 28 November 2017 / Revised: 21 December 2017 / Accepted: 27 December 2017 / Published: 1 January 2018
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Abstract
This paper presents experimental and numerical investigations on the characteristics of residual stresses generated by induction heating (IH) on 12 mm thick steel plates. IH at 250 °C and 350 °C provided high tensile residual stresses in the heating field but high compressive
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This paper presents experimental and numerical investigations on the characteristics of residual stresses generated by induction heating (IH) on 12 mm thick steel plates. IH at 250 °C and 350 °C provided high tensile residual stresses in the heating field but high compressive stresses away from the heating field. The double heating case generated higher compressive residual stresses—around 200 MPa—than the single heating case because of the superposition of the compressive residual stresses. It will be expected to improve the fatigue performance of welded joints when IH is applied for repair work on existing steel structural members susceptible to fatigue damage. Numerical simulation models for predicting residual stresses by IH were proposed by adopting the body heat flux input and the surface heat flux input. They will be beneficial for identifying the optimum heating conditions, such as the target temperature and the heating field, for applying IH to the actual repair work of the steel structural members. Full article
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Open AccessArticle Effect of Post Weld Heat Treatment on the Microstructure and Mechanical Properties of a Submerged-Arc-Welded 304 Stainless Steel
Metals 2018, 8(1), 26; https://doi.org/10.3390/met8010026
Received: 8 November 2017 / Revised: 15 December 2017 / Accepted: 22 December 2017 / Published: 2 January 2018
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Abstract
The present study is to investigate the effect of post heat treatment on the microstructures and mechanical properties of a submerged-arc-welded 304 stainless steel. The base material consisted of austenite and long strips of delta-ferrite surrounded by Cr-carbide, and the welds consisted of
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The present study is to investigate the effect of post heat treatment on the microstructures and mechanical properties of a submerged-arc-welded 304 stainless steel. The base material consisted of austenite and long strips of delta-ferrite surrounded by Cr-carbide, and the welds consisted of delta ferrite and austenite matrix. For the heat treatment at 850 °C or lower, Cr-carbides were precipitated in the weld metal resulting in the reduction of elongation. The strength, however, was slightly reduced despite the presence of Cr-carbides and this could possibly be explained by the relaxation of internal stress and the weakening of particle hardening. In the heat treatment at 1050 °C, the dissolution of Cr-carbide and disappearance of delta ferrite resulted in the lower yield strength and higher elongation partially assisted from deformation-induced martensitic transformation. Consequently, superior property in terms of fracture toughness was achieved by the heat treatment at 1050 °C, suggesting that the mechanical properties of the as-weld metal can be enhanced by controlling the post weld heat treatment. Full article
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Open AccessArticle Oxidation Behavior of Zr–1Nb Corroded in Air at 400 °C after Plasma Immersion Titanium Implantation
Metals 2018, 8(1), 27; https://doi.org/10.3390/met8010027
Received: 4 October 2017 / Revised: 24 December 2017 / Accepted: 30 December 2017 / Published: 2 January 2018
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Abstract
In this paper, the influence of plasma immersion titanium implantation into the zirconium alloy Zr-1Nb on the oxidation behavior at 400 °C for 5, 24, 72, and 240 h in air under normal atmospheric pressure (101.3 kPa) was shown. The influence of implantation
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In this paper, the influence of plasma immersion titanium implantation into the zirconium alloy Zr-1Nb on the oxidation behavior at 400 °C for 5, 24, 72, and 240 h in air under normal atmospheric pressure (101.3 kPa) was shown. The influence of implantation on the protective properties of the modified layer was shown. The valence of the oxides before and after implantation was analyzed by means of X-ray photoelectron spectroscopy (XPS). Grazing incidence X-ray diffraction (GIXRD) was carried out to examine the phase composition after titanium ion implantation and oxidation. Differential scanning calorimetry (DSC) revealed that titanium implantation exhibited effects of stabilizing the β phase. The formation of the t-ZrO2 and m-ZrO2 was observed during the oxidation of the as-received and modified Zr-1Nb. The measurement of weight gain showed an improvement in oxidation resistance of Ti implanted Zr-1Nb at the oxidation up to 24 h when compared with that of the as-received Zr-1Nb. However, at longer oxidation cycle the oxidation rate of Ti-implanted zirconium alloy is the same with the as-received alloy, which attributed to the layer thickness. Nevertheless, the corrosion of the Ti-implanted alloy is more uniform, while a local corrosion and cracks was detected on the surface of the as-received alloy. Full article
(This article belongs to the Special Issue Zirconium Alloys)
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Open AccessArticle High Hardness Nanocrystalline Invar Alloys Prepared from Fe-Ni Nanoparticles
Metals 2018, 8(1), 28; https://doi.org/10.3390/met8010028
Received: 24 November 2017 / Revised: 19 December 2017 / Accepted: 25 December 2017 / Published: 2 January 2018
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Abstract
High-density (>98% of full density) nanocrystalline invar alloys with significantly enhanced hardness (>240 in Vicker’s hardness) were prepared by sintering compacted Fe-Ni nanoparticles in hydrogen. The precursor Fe-Ni nanoparticles were synthesized by hydrogen plasma evaporation of bulk Fe61Ni39 alloys. The
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High-density (>98% of full density) nanocrystalline invar alloys with significantly enhanced hardness (>240 in Vicker’s hardness) were prepared by sintering compacted Fe-Ni nanoparticles in hydrogen. The precursor Fe-Ni nanoparticles were synthesized by hydrogen plasma evaporation of bulk Fe61Ni39 alloys. The size and the productivity of the Fe-Ni nanoparticles increased with increasing hydrogen pressure. The presence of surface oxidation of the Fe-Ni nanoparticles when exposed to air was proved by the X-ray photoelectron spectra measurements. The compacted Fe-Ni nanoparticles grew rapidly at 956 °C, while the oxide impurities were removed completely by following hydrogen at 735 °C, which was found to be optimum for the synthesis of oxide-free nanocrystalline metals with fine grain size. The typical hardness of an invar alloy prepared by melting method was around 140 HV. The significantly enhanced hardness of our nanocrystalline invar alloys was potentially important in strengthening the durability of its components in instruments and in improving its machinability when machining for a component. Full article
(This article belongs to the Special Issue Synthesis and Properties of Bulk Nanostructured Metallic Materials)
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Open AccessArticle Alkali Treatment of Anodized Titanium Alloys Affects Cytocompatibility
Metals 2018, 8(1), 29; https://doi.org/10.3390/met8010029
Received: 31 October 2017 / Revised: 27 December 2017 / Accepted: 28 December 2017 / Published: 3 January 2018
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Abstract
In this paper, the surface modification of titanium alloys Ti-15Mo, Ti-13Nb-13Zr, and Ti-6Al-7Nb is presented as a material for dental implants. The conditions of the plasma electrolytic oxidation process and alkali treatment were designed in this way to enhance the biological properties of
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In this paper, the surface modification of titanium alloys Ti-15Mo, Ti-13Nb-13Zr, and Ti-6Al-7Nb is presented as a material for dental implants. The conditions of the plasma electrolytic oxidation process and alkali treatment were designed in this way to enhance the biological properties of the surface of promising Ti alloys. The differences in their surface morphology and, consequently, in their biological properties were discussed. The bioactivity of the samples was examined in vitro using simulated body fluid, and Saos-2 osteoblast cells. On all the samples, characteristic apatite particles were formed. However, compared to as-ground, natively-oxidized bare alloys, the plasma electrolytic oxidation (PEO)-modified surface of the Ti-13Nb-13Zr alloy showed the highest cytocompatibility for Saos-2 osteoblast cells, and a beneficial gain of cytocompatibility was also achieved in the treated sample of Ti-6Al-7Nb. In contrast, the modification of the Ti-15Mo alloy did not influence the adhesion and proliferation of osteoblast cells. Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation)
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Open AccessFeature PaperArticle Ion Implantation of Calcium and Zinc in Magnesium for Biodegradable Implant Applications
Metals 2018, 8(1), 30; https://doi.org/10.3390/met8010030
Received: 8 December 2017 / Revised: 29 December 2017 / Accepted: 29 December 2017 / Published: 3 January 2018
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Abstract
In this study, magnesium was implanted with calcium-ion and zinc-ion at fluences of 1015, 1016, and 1017 ion·cm−2, and its in vitro degradation behaviour was evaluated using electrochemical techniques in simulated body fluid (SBF). Rutherford backscattering
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In this study, magnesium was implanted with calcium-ion and zinc-ion at fluences of 1015, 1016, and 1017 ion·cm−2, and its in vitro degradation behaviour was evaluated using electrochemical techniques in simulated body fluid (SBF). Rutherford backscattering spectrometry (RBS) revealed that the implanted ions formed layers within the passive magnesium-oxide/hydroxide layers. Electrochemical impedance spectroscopy (EIS) results demonstrated that calcium-ion implantation at a fluence of 1015 ions·cm−2 increased the polarisation resistance by 24%, but higher fluences showed no appreciable improvement. In the case of zinc-ion implantation, increase in the fluence decreased the polarisation resistance. A fluence of 1017 ion·cm−2 decreased the polarisation resistance by 65%, and fluences of 1015 and 1016 showed only marginal effect. Similarly, potentiodynamic polarisation results also suggested that low fluence of calcium-ion decreased the degradation rate by 38% and high fluence of zinc-ion increased the degradation rate by 61%. All the post-polarized ion-implanted samples and the bare metal revealed phosphate and carbonate formation. However, the improved degradative behaviour in calcium-ion implanted samples can be due to a relatively better passivation, whereas the reduction in degradation resistance in zinc-ion implanted samples can be attributed to the micro-galvanic effect. Full article
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Open AccessArticle Cryogenic Milling of Titanium Powder
Metals 2018, 8(1), 31; https://doi.org/10.3390/met8010031
Received: 29 November 2017 / Revised: 21 December 2017 / Accepted: 31 December 2017 / Published: 4 January 2018
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Abstract
Ti Grade 2 was prepared by cryogenic attritor milling in liquid nitrogen and liquid argon. Two types of milling balls were used—stainless steel balls and heavy tungsten carbide balls. The effect of processing parameters on particle size and morphology, contamination of powder and
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Ti Grade 2 was prepared by cryogenic attritor milling in liquid nitrogen and liquid argon. Two types of milling balls were used—stainless steel balls and heavy tungsten carbide balls. The effect of processing parameters on particle size and morphology, contamination of powder and its microhardness was investigated. Milling in liquid nitrogen was not feasible due to excessive contamination by nitrogen. Minor reduction of particle size and significant alterations in particle morphology depended on type of milling balls and application of stearic acid as processing control agent. Heavily deformed ultra-fine grained (UFG) internal microstructure of powder particles was observed by the method of “transmission Kikuchi diffraction”. Full article
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Open AccessFeature PaperArticle Low-Cycle Fatigue Behaviour of AISI 18Ni300 Maraging Steel Produced by Selective Laser Melting
Metals 2018, 8(1), 32; https://doi.org/10.3390/met8010032
Received: 1 December 2017 / Revised: 26 December 2017 / Accepted: 1 January 2018 / Published: 5 January 2018
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Abstract
Selective laser melting has received a great deal of attention in recent years. Nevertheless, research has been mainly focused on the technical issues and their relationship with the final microstructure and monotonic properties. Fatigue behaviour has rarely been addressed, and the emphasis has
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Selective laser melting has received a great deal of attention in recent years. Nevertheless, research has been mainly focused on the technical issues and their relationship with the final microstructure and monotonic properties. Fatigue behaviour has rarely been addressed, and the emphasis has been placed on high-cycle regimes. The aim of this paper is, therefore, to study, in a systematic manner, the cyclic plastic behaviour of AISI 18Ni300 maraging steel manufactured by selective laser melting. For this purpose, low-cycle fatigue tests, under fully-reversed strain-controlled conditions, with strain amplitudes ranging from 0.3% to 1.0%, were performed. After testing, fracture surfaces were examined by scanning electron microscopy to identify the main fatigue damage mechanisms. The analysis of results showed a non-Masing material, with a slight strain-softening behaviour, and non-linear response in both the elastic and plastic regimes. In addition, this steel exhibited a very low transition life of about 35 reversals, far below the values of conventional materials with equivalent monotonic mechanical properties, which can be attributed to the combination of high strength and low ductility. The total strain energy density, irrespective of strain amplitude, revealed itself to be a quite stable parameter throughout the lifetime. Finally, the SEM analysis showed for almost all the tested samples cracks initiated from the surface and inner defects which propagated through the rest of the cross section. A ductile/brittle fracture, with a predominance of brittle fracture, was observed in the samples, owing to the presence of defects which make it easier to spread the microcracks. Full article
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Open AccessArticle Formation Mechanisms for Entry and Exit Defects in Bobbin Friction Stir Welding
Metals 2018, 8(1), 33; https://doi.org/10.3390/met8010033
Received: 29 November 2017 / Revised: 29 December 2017 / Accepted: 3 January 2018 / Published: 5 January 2018
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Abstract
Bobbin friction stir welding (BFSW) is an innovative variant for the solid state welding process whereby a rotating symmetrical tool causes a fully penetrated bond. Despite the process development, there are still unknown variables in the characterization of the process parameters which can
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Bobbin friction stir welding (BFSW) is an innovative variant for the solid state welding process whereby a rotating symmetrical tool causes a fully penetrated bond. Despite the process development, there are still unknown variables in the characterization of the process parameters which can cause uncontrolled weld defects. The entry zone and the exit zone consist of two discontinuity-defects and removing them is one of the current challenges for improving the weld quality. In the present research, the characteristic features of the entry and exit defects in the weld structure and formation mechanism of them during the BFSW processing was investigated. Using stacked layers of multi-colour plasticine the material flow, analogous to metal flow, can be visualised. By using different colours as the path markers of the analogue model, the streamline flow can be easily delineated in the discontinuity defects compared with the metal welds. AA6082-T6 aluminium plates and multi-layered plasticine slabs were employed to replicate the entry-exit defects in the metal weld and analogue samples. The fixed-bobbin tool utilized for this research was optimized by adding a thread feature and tri-flat geometry to the pin and closed-end spiral scrolls on both shoulder surfaces. Samples were processed at different rotating and longitudinal speeds to show the degree of dependency on the welding parameters for the defects. The analogue models showed that the entry zone and the exit zone of the BFSW are affected by the inhomogeneity of the material flow regime which causes the ejection or disruption of the plastic flow in the gap between the bobbin shoulders. The trial aluminium welds showed that the elimination of entry-exit defects in the weld body is not completely possible but the size of the defects can be minimized by modification of the welding parameters. For the entry zone, the flow pattern evolution suggested formation mechanisms for a sprayed tail, island zone and discontinuity-channel. For the exit zone a keyhole-shaped discontinuity is discussed as a structural defect. Full article
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Open AccessArticle Ab Initio-Based Modelling of the Yield Strength in High-Manganese Steels
Metals 2018, 8(1), 34; https://doi.org/10.3390/met8010034
Received: 15 November 2017 / Revised: 16 December 2017 / Accepted: 3 January 2018 / Published: 5 January 2018
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Abstract
An ab initio-based model for the strength increase by short-range ordering of C-Mn-Al clusters has been developed. The model is based on ab initio calculations of ordering energies. The impact of clusters on the yield strength of high-manganese austenitic steels (HMnS) is highly
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An ab initio-based model for the strength increase by short-range ordering of C-Mn-Al clusters has been developed. The model is based on ab initio calculations of ordering energies. The impact of clusters on the yield strength of high-manganese austenitic steels (HMnS) is highly dependent on the configurational structure of the cells that carbon atoms will position themselves as interstitial atoms. The impact of the alloying elements C, Mn, and Al on the potential and actual increase in yield strength is analyzed. A model for the calculation of yield strengths of HMnS is derived that includes the impact of short-range ordering, grain size refinement, and solid solution strengthening. The model is in good agreement with experimental data and performs better than other models that do not include strengthening by short-range ordering. Full article
(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)
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Open AccessArticle The Evolution of Cast Microstructures on the HAZ Liquation Cracking of Mar-M004 Weld
Metals 2018, 8(1), 35; https://doi.org/10.3390/met8010035
Received: 31 October 2017 / Revised: 22 December 2017 / Accepted: 3 January 2018 / Published: 5 January 2018
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Abstract
The causes of liquation cracking in the heat-affected zone (HAZ) of a cast Mar-M004 superalloy weld were investigated. X-ray diffraction (XRD), electron probe microanalyzer (EPMA), and electron backscatter diffraction (EBSD) were applied to identify the final microconstituents at the solidification boundaries of the
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The causes of liquation cracking in the heat-affected zone (HAZ) of a cast Mar-M004 superalloy weld were investigated. X-ray diffraction (XRD), electron probe microanalyzer (EPMA), and electron backscatter diffraction (EBSD) were applied to identify the final microconstituents at the solidification boundaries of the cast alloy. Fine borides and lamellar eutectics were present in front of some γ-γ′ colonies, which were expected to be liquefied prematurely during welding. The metal carbide (MC) enriched in Nb, Hf; M3B2 and M5B3 borides enriched in Cr and Mo; and lamellar Ni-Hf intermetallics were mainly responsible for the induced liquation cracking of the Mar-M004 weld, especially the MC carbides. Scanning electron microscope (SEM) fractographs showed that the fracture features of those liquation cracks were associated with the interdendritic constituents in the cast superalloy. Full article
(This article belongs to the Special Issue Alloys for High-Temperature Applications)
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Open AccessArticle Failure Analysis and Reliability of Ni–Ti-Based Dental Rotary Files Subjected to Cyclic Fatigue
Metals 2018, 8(1), 36; https://doi.org/10.3390/met8010036
Received: 12 November 2017 / Revised: 29 December 2017 / Accepted: 3 January 2018 / Published: 6 January 2018
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Abstract
The cyclic fatigue resistance of ProTaper Universal (PTU), ProTaper Gold (PTG), and ProTaper Next (PTN) nickel titanium (NiTi) rotary files was evaluated. Fifteen instruments of each type were selected, totaling 195 files. The instruments were rotated until fracture in an artificial canal with
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The cyclic fatigue resistance of ProTaper Universal (PTU), ProTaper Gold (PTG), and ProTaper Next (PTN) nickel titanium (NiTi) rotary files was evaluated. Fifteen instruments of each type were selected, totaling 195 files. The instruments were rotated until fracture in an artificial canal with dimensions corresponding to the dimensions of each instrument tested: +0.1 mm in width and 0.2 mm in depth, an angle of curvature of 45°, a radius of curvature of 5 mm, and a center of curvature 5 mm from the instrument tip. The fracture surfaces of three representative samples of each subgroup were examined using scanning electron microscopy (SEM). Time to fracture was analyzed via analysis of variance and Tukey’s tests (P < 0.05). PTG F1 and F2 had significantly higher resistance than PTU F1 and PTN X2, and PTU F2 and PTN X3, respectively. PTN X2 showed a significantly higher resistance than PTU F1. The PTG series demonstrated superior cyclic fatigue (CF) behavior compared with that of the PTU and PTN series. Full article
(This article belongs to the Special Issue Failure Analysis of Biometals)
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Open AccessArticle Influence of Heat Treatment and UV Irradiation on the Wettability of Ti35Nb10Ta Nanotubes
Metals 2018, 8(1), 37; https://doi.org/10.3390/met8010037
Received: 18 November 2017 / Revised: 21 December 2017 / Accepted: 29 December 2017 / Published: 7 January 2018
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Abstract
The implant osseointegration rate depends on the surface’s topography and chemical composition. There is a growing interest in the anodic oxidation process to obtain an oxide layer with a nanotube morphology on beta titanium alloys. This surface treatment presents large surface area, nanoscale
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The implant osseointegration rate depends on the surface’s topography and chemical composition. There is a growing interest in the anodic oxidation process to obtain an oxide layer with a nanotube morphology on beta titanium alloys. This surface treatment presents large surface area, nanoscale rugosity and electrochemical properties that may increase the biocompatibility and osseointegration rate in titanium implants. In this work, an anodic oxidation process was used to modify the surface on the Ti35Nb10Ta alloy to obtain a titanium nanotubes topography. The work focused on analyzing the influence of some variables (voltage, heat treatment and ultraviolet irradiation) on the wettability performance of a titanium alloy. The morphology of the nanotubes surfaces was studied by Field Emission Scanning Electron Microscopy (FESEM), and surface composition was analyzed by Energy Dispersive Spectroscopy (EDS). The measurement of contact angle for the TiO2 nanotube surfaces was measured by a video contact angle system. The surface with the non photoinduced nanotubes presented the largest contact angles. The post-heat treatment lowered the F/Ti ratio in the nanotubes and decreased the contact angle. Ultraviolet (UV) irradiation of the TiO2 nanotubes decrease the water contact angle. Full article
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Open AccessArticle Extraction of Iron and Manganese from Pyrolusite Absorption Residue by Ammonium Sulphate Roasting–Leaching Process
Metals 2018, 8(1), 38; https://doi.org/10.3390/met8010038
Received: 21 December 2017 / Revised: 31 December 2017 / Accepted: 5 January 2018 / Published: 8 January 2018
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Abstract
The residue from desulfurization and denitrification of exhaust gas treatment process with pyrolusite ore as absorbent is regarded as a potential source of iron and manganese. In this study, an extraction process is proposed for recovery of iron and manganese with ammonium sulphate
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The residue from desulfurization and denitrification of exhaust gas treatment process with pyrolusite ore as absorbent is regarded as a potential source of iron and manganese. In this study, an extraction process is proposed for recovery of iron and manganese with ammonium sulphate roasting followed by sulphuric acid leaching. Firstly, the conversion mechanism was analyzed through mineral phase analysis of roasting products at different roasting temperature by means of X-ray diffraction (XRD) technology. Then, the parameters of the roasting procedure such as roasting temperature and time, ammonium sulphate dosage, leaching temperature, leaching time, and sulphuric acid concentration are examined. The results implicate that the iron oxide and manganese dioxide in the residue are firstly converted into the water-soluble ( NH 4 ) 3 Fe ( SO 4 ) 3 and ( NH 4 ) 2 Mn 2 ( SO 4 ) 3 at 200–350 °C, and then the more stable NH 4 Fe ( SO 4 ) 2 and MnSO 4 are formed, at temperature higher than 350 °C. Under optimum conditions, 95.2% Fe and 97.0% Mn can be extracted. Reactant diffusion through inert layer of silicon dioxide was considered as the rate-limiting step for iron extraction with an activation energy of 20.56 kJ/mol, while, the recovery process of Mn was controlled by both reactant diffusion and chemical reaction with an activation energy of 29.52 kJ/mol. Full article
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Open AccessArticle Precipitation Stages and Reaction Kinetics of AlMgSi Alloys during the Artificial Aging Process Monitored by In-Situ Electrical Resistivity Measurement Method
Metals 2018, 8(1), 39; https://doi.org/10.3390/met8010039
Received: 4 December 2017 / Revised: 1 January 2018 / Accepted: 5 January 2018 / Published: 11 January 2018
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Abstract
The precipitation process and reaction kinetics during artificial aging, precipitate microstructure, and mechanical properties after aging of AlMgSi alloys were investigated employing in-situ electrical resistivity measurement, Transmission Electron Microscopy (TEM) observation, and tensile test methods. Three aging stages in sequence, namely formation of
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The precipitation process and reaction kinetics during artificial aging, precipitate microstructure, and mechanical properties after aging of AlMgSi alloys were investigated employing in-situ electrical resistivity measurement, Transmission Electron Microscopy (TEM) observation, and tensile test methods. Three aging stages in sequence, namely formation of GP zones, transition from GP zones to β″ phase, transition from β″ to β′ phase, and coarsening of both phases, were clearly distinguished by the variation of the resistivity. It was discussed together with the mechanical properties and precipitate morphology evolution. Fast formation of GP zones and β″ phase leads to an obvious decrease of the resistivity and increase of the mechanical strength. The formation of β″ phase in the second stage, which contributes to the peak aging strength, has much higher reaction kinetics than reactions in the other two stages. All of these stages finished faster with higher reaction kinetics under higher temperatures, due to higher atom diffusion capacity. The results proved that the in-situ electrical resistivity method, as proposed in the current study, is a simple, effective, and convenient technique for real-time monitoring of the precipitation process of AlMgSi alloys. Its further application for industrial production and scientific research is also evaluated. Full article
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Open AccessArticle Hydrometallurgical Approach for Leaching of Metals from Copper Rich Side Stream Originating from Base Metal Production
Metals 2018, 8(1), 40; https://doi.org/10.3390/met8010040
Received: 17 November 2017 / Revised: 1 January 2018 / Accepted: 5 January 2018 / Published: 8 January 2018
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Abstract
Pyrometallurgical metal production results in side streams, such as dusts and slags, which are carriers of metals, though commonly containing lower metal concentrations compared to the main process stream. In order to improve the circular economy of metals, selective leaching of copper from
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Pyrometallurgical metal production results in side streams, such as dusts and slags, which are carriers of metals, though commonly containing lower metal concentrations compared to the main process stream. In order to improve the circular economy of metals, selective leaching of copper from an intermediate raw material originating from primary base metal production plant was investigated. The raw material investigated was rich in Cu (12.5%), Ni (2.6%), Zn (1.6%), and Fe (23.6%) with the particle size D80 of 124 µm. The main compounds present were nickel ferrite (NiFe2O4), fayalite (Fe2SiO4), cuprite (Cu2O), and metallic copper. Leaching was studied in 16 different solutions. The results revealed that copper phases could be dissolved with high yield (>90%) and selectivity towards nickel (Cu/Ni > 7) already at room temperature with the following solutions: 0.5 M HCl, 1.5 M HCl, 4 M NaOH, and 2 M HNO3. A concentration of 4 M NaOH provided a superior selectivity between Cu/Ni (340) and Cu/Zn (51). In addition, 1–2 M HNO3 and 0.5 M HCl solutions were shown to result in high Pb dissolution (>98%). Consequently, 0.5 M HCl leaching is suggested to provide a low temperature, low chemical consumption method for selective copper removal from the investigated side stream, resulting in PLS (pregnant leach solution) which is a rich in Cu and lead free residue, also rich in Ni and Fe. Full article
(This article belongs to the Special Issue Advances in Hydrometallurgy)
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Open AccessFeature PaperArticle A Microstructural Evaluation of Friction Stir Welded 7075 Aluminum Rolled Plate Heat Treated to the Semi-Solid State
Metals 2018, 8(1), 41; https://doi.org/10.3390/met8010041
Received: 5 December 2017 / Revised: 3 January 2018 / Accepted: 5 January 2018 / Published: 9 January 2018
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Abstract
Two rolled plates of 7075 aluminum alloy were used as starting material. The plates were welded using a simultaneous double-sided friction stir welding (FSW) process. One way of obtaining feedstock materials for Semi-solid processing or thixoforming is via deformation routes followed by partial
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Two rolled plates of 7075 aluminum alloy were used as starting material. The plates were welded using a simultaneous double-sided friction stir welding (FSW) process. One way of obtaining feedstock materials for Semi-solid processing or thixoforming is via deformation routes followed by partial melting in the semi-solid state. As both the base plate materials and the friction weld area have undergone extensive deformation specimens were subjected to a post welding heat-treatment in the semi-solid range at a temperature of 628 °C, for 3 min in order to observe the induced microstructural changes. A comparison between the microstructural evolution and mechanical properties of friction stir welded plates was performed before and after the heat-treatment in the Base Metal (BM), the Heat Affected Zone (HAZ), the Thermomechanically Affected Zone (TMAZ) and the Nugget Zone (NZ) using optical microscopy, Scanning Electron microscopy (SEM) and Vickers hardness tests. The results revealed that an extremely fine-grained structure, obtained in the NZ after FSW, resulted in a rise of hardness from the BM to the NZ. Furthermore, post welding heat-treatment in the semi-solid state gave rise to a consistent morphology throughout the material which was similar to microstructures obtained by the thixoforming process. Moreover, a drop of hardness was observed after heat treatment in all regions as compared to that in the welded microstructure. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Casting Alloys)
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Open AccessArticle Mechanism of Solder Joint Cracks in Anisotropic Conductive Films Bonding and Solutions: Delaying Hot-Bar Lift-Up Time and Adding Silica Fillers
Metals 2018, 8(1), 42; https://doi.org/10.3390/met8010042
Received: 11 December 2017 / Revised: 2 January 2018 / Accepted: 3 January 2018 / Published: 9 January 2018
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Abstract
Micron sizes solder metallurgical joints have been applied in a thin film application of anisotropic conductive film and benefited three general advantages, such as lower joint resistance, higher power handling capability, and reliability, when compared with pressure based contact of metal conductor balls.
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Micron sizes solder metallurgical joints have been applied in a thin film application of anisotropic conductive film and benefited three general advantages, such as lower joint resistance, higher power handling capability, and reliability, when compared with pressure based contact of metal conductor balls. Recently, flex-on-board interconnection has become more and more popular for mobile electronic applications. However, crack formation of the solder joint crack was occurred at low temperature curable acrylic polymer resins after bonding processes. In this study, the mechanism of SnBi58 solder joint crack at low temperature curable acrylic adhesive was investigated. In addition, SnBi58 solder joint cracks can be significantly removed by increasing the storage modulus of adhesives instead of coefficient of thermal expansion. The first approach of reducing the amount of polymer rebound can be achieved by using an ultrasonic bonding method to maintain a bonding pressure on the SnBi58 solder joints cooling to room temperature. The second approach is to increase storage modulus of adhesives by adding silica filler into acrylic polymer resins to prevent the solder joint from cracking. Finally, excellent acrylic based SnBi58 solder joints reliability were obtained after 1000 cycles thermal cycling test. Full article
(This article belongs to the Special Issue Science, Characterization and Technology of Joining and Welding)
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Open AccessArticle Temperature and Particle Size Influence on the High Cycle Fatigue Behavior of the SiC Reinforced 2124 Aluminum Alloy
Metals 2018, 8(1), 43; https://doi.org/10.3390/met8010043
Received: 11 December 2017 / Revised: 5 January 2018 / Accepted: 8 January 2018 / Published: 10 January 2018
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Abstract
In this work the high cycle fatigue behavior of a particulate reinforced 2124 aluminum alloy, manufactured by powder metallurgy, is investigated. SiC particles with a size of 3 μm and 300 nm and a volume fraction of 5 and 25 vol %, respectively,
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In this work the high cycle fatigue behavior of a particulate reinforced 2124 aluminum alloy, manufactured by powder metallurgy, is investigated. SiC particles with a size of 3 μm and 300 nm and a volume fraction of 5 and 25 vol %, respectively, were used as reinforcement component. The present study is focused on the fatigue strength and the influence of particle size and temperature. Systematic work is done by comparing the unreinforced alloy and the reinforced conditions. All of the material conditions are characterized by electron microscopy and tensile and fatigue testing at room temperature and at 180 °C. With an increase in temperature the tensile and the fatigue strength decrease, regardless of particle size and volume fraction due to the lower matrix strength. The combination of 25 vol % SiC particle fraction with 3 μm size proved to be most suitable to achieve a major fatigue performance at room temperature and at 180 °C. The fatigue strength is increased by 40% when compared to the unreinforced alloy, as it is assumed the interparticle spacing for this condition reaches a critical value then. Full article
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Open AccessFeature PaperArticle On the Mn–C Short-Range Ordering in a High-Strength High-Ductility Steel: Small Angle Neutron Scattering and Ab Initio Investigation
Metals 2018, 8(1), 44; https://doi.org/10.3390/met8010044
Received: 29 November 2017 / Revised: 3 January 2018 / Accepted: 5 January 2018 / Published: 10 January 2018
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Abstract
The formation of Mn–C short-range ordering (SRO) has a great influence on the mechanical properties of high-Mn steels. In the present work, the formation of Mn–C SRO during recrystallization of an X60Mn18 steel was investigated by means of a combined study employing small
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The formation of Mn–C short-range ordering (SRO) has a great influence on the mechanical properties of high-Mn steels. In the present work, the formation of Mn–C SRO during recrystallization of an X60Mn18 steel was investigated by means of a combined study employing small angle neutron scattering (SANS) and ab initio ground-state energy calculations based on density-functional theory. The SANS measurements prove the presence of Mn–C SRO in the recrystallization annealed X60Mn18 steel and indicate the evolution of the SRO during recrystallization. The results show that with the increase in annealing time, the mean size of the Mn–C SRO decreases, whereas the number density increases. The ab initio calculations well describe the energetically favored condition of Mn–C SRO and provide the theoretical explanation of the clustering formation and evolution in the X60Mn18 steel. The stress-strain curve of the X60Mn18 steel exhibits a high strain-hardening rate and the plastic deformation is characterized with a series of serrations during a uniaxial tensile test. In the end, the correlation between Mn–C SRO and the serrated flow of high-Mn steels is further discussed. Full article
(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)
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Open AccessArticle Discrete Optimization of Internal Part Structure via SLM Unit Structure-Performance Database
Metals 2018, 8(1), 45; https://doi.org/10.3390/met8010045
Received: 15 November 2017 / Revised: 4 January 2018 / Accepted: 5 January 2018 / Published: 11 January 2018
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Abstract
The structural optimization of the internal structure of parts based on three-dimensional (3D) printing has been recognized as being important in the field of mechanical design. The purpose of this paper is to present a creation of a unit structure-performance database based on
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The structural optimization of the internal structure of parts based on three-dimensional (3D) printing has been recognized as being important in the field of mechanical design. The purpose of this paper is to present a creation of a unit structure-performance database based on the selective laser melting (SLM), which contains various structural units with different functions and records their structure and performance characteristics so that we can optimize the internal structure of parts directly, according to the database. The method of creating the unit structure-performance database was introduced in this paper and several structural units of the unit structure-performance database were introduced. The bow structure unit was used to show how to create the structure-performance database of the unit as an example. Some samples of the bow structure unit were designed and manufactured by SLM. These samples were tested in the WDW-100 compression testing machine to obtain their performance characteristics. After this, the paper collected all data regarding unit structure parameters, weight, performance characteristics, and other data; and, established a complete set of data from the bow structure unit for the unit structure-performance database. Furthermore, an aircraft part was reconstructed conveniently to be more lightweight according to the unit structure-performance database. Its weight was reduced by 36.8% when compared with the original structure, while the strength far exceeded the requirements. Full article
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Open AccessArticle Direct Numerical Study of a Molten Metal Drop Solidifying on a Cold Plate with Different Wettability
Metals 2018, 8(1), 47; https://doi.org/10.3390/met8010047
Received: 21 December 2017 / Revised: 3 January 2018 / Accepted: 8 January 2018 / Published: 11 January 2018
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Abstract
This paper presents a direct numerical simulation of solidification of a molten metal drop on a cold plate with various wettability by an axisymmetric front-tracking method. Because of the plate kept at a temperature below the fusion value of the melt, a thin
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This paper presents a direct numerical simulation of solidification of a molten metal drop on a cold plate with various wettability by an axisymmetric front-tracking method. Because of the plate kept at a temperature below the fusion value of the melt, a thin solid layer forms at the plate and evolves upwards. The numerical results show that the solidifying front is almost flat except near the triple point with a high solidification rate at the beginning and final stages of solidification. Two solid-to-liquid density ratios ρsl = 0.9 (volume change) and 1.0 (no change in volume), with two growth angles φ0 = 0° and 12° are considered. The presence of volume change and a non-zero growth angle results in a solidified drop with a conical shape at the top. The focusing issue is the effects of the wettability of the plate in terms of the contact angle φ0. Increasing the contact angle in the range of 45° to 120° increases time for completing solidification, i.e., solidification time. However, it has a minor effect on the conical angle at the top of the solidified drop and the difference between the initial liquid and final solidified heights of the drop. The effects of the density ratio and growth angle are also presented. Full article
(This article belongs to the Special Issue Rapid Solidification Processing)
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Open AccessArticle Microstructure and Tensile-Shear Properties of Resistance Spot-Welded Medium Mn Steel
Metals 2018, 8(1), 48; https://doi.org/10.3390/met8010048
Received: 10 December 2017 / Revised: 4 January 2018 / Accepted: 5 January 2018 / Published: 11 January 2018
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Abstract
The medium Mn steels are gaining increasing attention due to their excellent combination of mechanical properties and material cost. A cold-rolled 0.1C5Mn medium Mn steel with a ferrite matrix plus metastable austenite duplex microstructure was resistance spot-welded with various welding currents and times.
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The medium Mn steels are gaining increasing attention due to their excellent combination of mechanical properties and material cost. A cold-rolled 0.1C5Mn medium Mn steel with a ferrite matrix plus metastable austenite duplex microstructure was resistance spot-welded with various welding currents and times. The nugget size rose with the increase of heat input, but when the welding current exceeded the critical value, the tensile-shear load increased slowly and became unstable due to metal expulsion. The fusion zone exhibited a lath martensite microstructure, and the heat-affected zone was composed of a ferrite/martensite matrix with retained austenite. The volume fraction of retained austenite decreased gradually from the base metal to the fusion zone, while the microhardness presented a reverse varying trend. Interfacial failure occurred along the interface of the steel sheets with lower loading capacity. Sufficient heat input along with serious expulsion brought about high stress concentration around the weld nugget, and the joint failed in partial interfacial mode. Pull-out failure was absent in this study. Full article
(This article belongs to the Special Issue Medium-Mn Steels, a Promising Type of the 3rd Generation Steels)
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Open AccessArticle In Situ Spectroscopic Analysis of the Carbothermal Reduction Process of Iron Oxides during Microwave Irradiation
Metals 2018, 8(1), 49; https://doi.org/10.3390/met8010049
Received: 25 December 2017 / Revised: 9 January 2018 / Accepted: 9 January 2018 / Published: 11 January 2018
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Abstract
The effects of microwave plasma induction and reduction on the promotion of the carbothermal reduction of iron oxides (α-Fe2O3, γ-Fe2O3, and Fe3O4) are investigated using in situ emission spectroscopy measurements during
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The effects of microwave plasma induction and reduction on the promotion of the carbothermal reduction of iron oxides (α-Fe2O3, γ-Fe2O3, and Fe3O4) are investigated using in situ emission spectroscopy measurements during 2.45 GHz microwave processing, and the plasma discharge (such as CN and N2) is measured during microwave E-field irradiation. It is shown that CN gas or excited CN molecules contribute to the iron oxide reduction reactions, as well as to the thermal reduction. On the other hand, no plasma is generated during microwave H-field irradiation, resulting in thermal reduction. Magnetite strongly interacts with the microwave H-field, and the reduction reaction is clearly promoted by microwave H-field irradiation, as well as thermal reduction reaction. Full article
(This article belongs to the Special Issue Ironmaking and Steelmaking)
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Open AccessFeature PaperArticle Mechanical and Tribological Properties of Al2O3-TiC Composite Fabricated by Spark Plasma Sintering Process with Metallic (Ni, Nb) Binders
Metals 2018, 8(1), 50; https://doi.org/10.3390/met8010050
Received: 21 December 2017 / Revised: 6 January 2018 / Accepted: 10 January 2018 / Published: 12 January 2018
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Abstract
Al2O3-10TiC composites were fabricated through the powder metallurgical process (mechanical milling combined with spark plasma sintering) with the addition of Ni/Nb as metallic binders. The effect of binder addition (Ni/Nb) on the processing, microstructure, and mechanical and tribological properties
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Al2O3-10TiC composites were fabricated through the powder metallurgical process (mechanical milling combined with spark plasma sintering) with the addition of Ni/Nb as metallic binders. The effect of binder addition (Ni/Nb) on the processing, microstructure, and mechanical and tribological properties of the bulk-sintered composite samples was investigated. The microstructure of the composite reveals a homogeneous distribution of the TiC particles in the Al2O3 matrix. However, the presence of Ni/Nb was not traceable, owing to the small amounts of Ni/Nb addition. Hardness and density of the composite samples increase with the increasing addition of Nb (up to 2 wt. % Nb). Any further increase in the Nb content (3 wt. %) decreases both the hardness and the wear resistance. However, in case of Ni as binder, both the hardness and wear resistance increases with the increase in the Ni content from 1 wt. % to 3 wt. %. However, the composite samples with Nb as binder show improved hardness and wear resistance compared to the composites with Ni as binder. Full article
(This article belongs to the Special Issue Cermets and Hardmetals)
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Open AccessArticle Influence of Extrusion Temperature on the Aging Behavior and Mechanical Properties of an AA6060 Aluminum Alloy
Metals 2018, 8(1), 51; https://doi.org/10.3390/met8010051
Received: 12 December 2017 / Revised: 3 January 2018 / Accepted: 9 January 2018 / Published: 12 January 2018
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Abstract
Processing of AA6060 aluminum alloys for semi-products usually includes hot extrusion with subsequent artificial aging for several hours. Processing below the recrystallization temperature allows for an increased strength at a significantly reduced annealing time by combining strain hardening and precipitation hardening. In this
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Processing of AA6060 aluminum alloys for semi-products usually includes hot extrusion with subsequent artificial aging for several hours. Processing below the recrystallization temperature allows for an increased strength at a significantly reduced annealing time by combining strain hardening and precipitation hardening. In this study, we investigate the potential of cold and warm extrusion as alternative processing routes for high strength aluminum semi-products. Cast billets of the age hardening aluminum alloy AA6060 were solution annealed and then extruded at room temperature, 120 or 170 °C, followed by an aging treatment. Electron microscopy and mechanical testing were performed on the as-extruded as well as the annealed materials to characterize the resulting microstructural features and mechanical properties. All of the extruded profiles exhibit similar, strongly graded microstructures. The strain gradients and the varying extrusion temperatures lead to different stages of dynamic precipitation in the as-extruded materials, which significantly alter the subsequent aging behavior and mechanical properties. The experimental results demonstrate that extrusion below recrystallization temperature allows for high strength at a massively reduced aging time due to dynamic precipitation and/or accelerated precipitation kinetics. The highest strength and ductility were achieved by extrusion at 120 °C and subsequent short-time aging. Full article
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Open AccessArticle The Corrosion Behavior of Ti-Based Metallic Glass Matrix Composites in the H2SO4 Solution
Metals 2018, 8(1), 52; https://doi.org/10.3390/met8010052
Received: 6 December 2017 / Revised: 4 January 2018 / Accepted: 4 January 2018 / Published: 17 January 2018
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Abstract
In-situ metallic glass matrix composites (MGMCs) are a new kind of promising structural engineering material. In this study, a comprehensive study about the corrosion behavior of in-situ Ti46Zr20V12Cu5Be17 MGMCs versus their size was conducted.
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In-situ metallic glass matrix composites (MGMCs) are a new kind of promising structural engineering material. In this study, a comprehensive study about the corrosion behavior of in-situ Ti46Zr20V12Cu5Be17 MGMCs versus their size was conducted. It is interesting to find that the large sample exhibits a more excellent corrosion resistance than the small sample in the 10% H2SO4 solution both in chemical and electrochemical tests at room temperature. Furthermore, the results obtained from X-ray photoelectron spectra (XPS) demonstrate that the quality of the passive film formed on the large-sized sample is indeed superior to the small-sized sample. Based on (scanning electron microscope) SEM observation, the possible mechanisms of the observed phenomenon have been discussed in the present study. Full article
(This article belongs to the Special Issue Metallic Glasses: Pathways to Viable Applications)
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Open AccessArticle Austempered Ductile Iron (ADI): Influence of Austempering Temperature on Microstructure, Mechanical and Wear Properties and Energy Consumption
Metals 2018, 8(1), 53; https://doi.org/10.3390/met8010053
Received: 23 November 2017 / Revised: 18 December 2017 / Accepted: 22 December 2017 / Published: 12 January 2018
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Abstract
Alloyed Ductile iron, austenitized at 840 °C for 30 min in a special sealed austempering furnace, was austempered for 30 min in molten salt mixture at 4 trial temperatures of 300 °C, 320 °C, 340 °C and 360 °C. Tensile strength, yield strength,
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Alloyed Ductile iron, austenitized at 840 °C for 30 min in a special sealed austempering furnace, was austempered for 30 min in molten salt mixture at 4 trial temperatures of 300 °C, 320 °C, 340 °C and 360 °C. Tensile strength, yield strength, percentage elongation and impact energy were evaluated for the as-cast and austempered samples. Microstructures were investigated using microscopy, coupled with analyzing software and a scanning electron microscopy. The specific wear of samples was tested using pin-on-disc wear testing machine. X-ray diffraction was performed to calculate the amount of retained austenite present in the ausferrite matrix. As-cast microstructure consists of ferrite and pearlite, whereas austempered ductile iron (ADI) contains a mixture of acicular ferrite and carbon enriched austenite, called “ausferrite”. Hardness and strength decreased, whereas ductility and impact strength improved with an increase in the austempering temperature. XRD analysis revealed that the increase in austempering temperature increased the retained austenite content. A decrease in wear resistance with austempering temperature was observed. Modified Quality Index (MQI) values were envisaged, incorporating tensile strength, elongation and wear resistance. MQI for samples austempered at 340 °C and 360 °C showed a better combination of properties. About an 8% reduction in energy consumption was gained when the heat treatment parameters were optimized. Full article
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Open AccessArticle Compositional Approach to Designing Fcc High-Entropy Alloys that Have an Enlarged Equiaxed Zone
Metals 2018, 8(1), 54; https://doi.org/10.3390/met8010054
Received: 26 December 2017 / Revised: 7 January 2018 / Accepted: 8 January 2018 / Published: 13 January 2018
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Abstract
A compositional approach to designing alloys that have an enlarged equiaxed zone is suggested in this study. The partitioning of elements during the solidification of CoCrFeMnNi high-entropy alloy (HEA) was confirmed through a directional solidification quenching experiment. Several HEAs were designed to maximize
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A compositional approach to designing alloys that have an enlarged equiaxed zone is suggested in this study. The partitioning of elements during the solidification of CoCrFeMnNi high-entropy alloy (HEA) was confirmed through a directional solidification quenching experiment. Several HEAs were designed to maximize the effects of constitutional and thermal undercooling by considering factors including solute enrichment at the columnar front and the melting temperatures and thermal conductivities of the individual elements. The newly designed HEAs were shown to have successfully enlarged equiaxed zones, and improved anisotropic properties. Full article
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Open AccessFeature PaperArticle Strain Localization during Equal-Channel Angular Pressing Analyzed by Finite Element Simulations
Metals 2018, 8(1), 55; https://doi.org/10.3390/met8010055
Received: 19 December 2017 / Revised: 6 January 2018 / Accepted: 8 January 2018 / Published: 15 January 2018
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Abstract
Equal-Channel Angular Pressing (ECAP) is a method used to introduce severe plastic deformation into a metallic billet without changing its geometry. In special cases, strain localization occurs and a pattern consisting of regions with high and low deformation (so-called shear and matrix bands)
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Equal-Channel Angular Pressing (ECAP) is a method used to introduce severe plastic deformation into a metallic billet without changing its geometry. In special cases, strain localization occurs and a pattern consisting of regions with high and low deformation (so-called shear and matrix bands) can emerge. This paper studies this phenomenon numerically adopting two-dimensional finite element simulations of one ECAP pass. The mechanical behavior of aluminum is modeled using phenomenological plasticity theory with isotropic or kinematic hardening. The effects of the two different strain hardening types are investigated numerically by systematic parameter studies: while isotropic hardening only causes minor fluctuations in the plastic strain fields, a material with high initial hardening rate and sufficient strain hardening capacity can exhibit pronounced localized deformation after ECAP. The corresponding finite element simulation results show a regular pattern of shear and matrix bands. This result is confirmed experimentally by ECAP-processing of AA6060 material in a severely cold worked condition, where microstructural analysis also reveals the formation of shear and matrix bands. Excellent agreement is found between the experimental and numerical results in terms of shear and matrix band width and length scale. The simulations provide additional insights regarding the evolution of the strain and stress states in shear and matrix bands. Full article
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Open AccessArticle Numerical Simulation of Tensile Behavior of Corroded Aluminum Alloy 2024 T3 Considering the Hydrogen Embrittlement
Metals 2018, 8(1), 56; https://doi.org/10.3390/met8010056
Received: 31 October 2017 / Revised: 21 December 2017 / Accepted: 10 January 2018 / Published: 15 January 2018
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Abstract
A multi-scale modeling approach for simulating the tensile behavior of the corroded aluminum alloy 2024 T3 was developed, accounting for both the geometrical features of corrosion damage and the effect of corrosion-induced hydrogen embrittlement (HE). The approach combines two Finite Element (FE) models:
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A multi-scale modeling approach for simulating the tensile behavior of the corroded aluminum alloy 2024 T3 was developed, accounting for both the geometrical features of corrosion damage and the effect of corrosion-induced hydrogen embrittlement (HE). The approach combines two Finite Element (FE) models: a model of a three-dimensional Representative Unit Cell (RUC), representing an exfoliated area and its correspondent hydrogen embrittled zone (HEZ), and a model of the tensile specimen. The models lie at the micro- and macro-scales, respectively. The characteristics of the HEZ are determined from measurements of nanoindentation hardness, conducted on pre-corroded specimens. Using the model of the RUC, the local homogenized mechanical behavior of the corroded material is simulated. Then, the behavior of the exfoliated areas is assigned into different areas (elements) of the tensile specimen and final analyses are performed to simulate the tensile behavior of the corroded material. The approach was applied to model specimens after 8, 16 and 24 h exposure periods of the Exfoliation Corrosion (EXCO) test. For validation of the approach, tensile tests were used. The numerical results show that this approach is suitable for accurately simulating the tensile behavior of pre-corroded experimental specimens, accounting for both geometrical features of corrosion damage and corrosion-induced HE. Full article
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Open AccessArticle Chemical Degradation of a Mixture of tri-n-Octylamine and 1-Tridecanol in the Presence of Chromium(VI) in Acidic Sulfate Media
Metals 2018, 8(1), 57; https://doi.org/10.3390/met8010057
Received: 9 December 2017 / Revised: 8 January 2018 / Accepted: 13 January 2018 / Published: 15 January 2018
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Abstract
The chemical degradation of an extraction solvent composed of a mixture of tri-n-octylamine (extractant) and 1-tridecanol (phase modifier) in n-dodecane in contact with an acidic aqueous sulfate solution containing chromium(VI) has been investigated. The kinetics of degradation and the degradation
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The chemical degradation of an extraction solvent composed of a mixture of tri-n-octylamine (extractant) and 1-tridecanol (phase modifier) in n-dodecane in contact with an acidic aqueous sulfate solution containing chromium(VI) has been investigated. The kinetics of degradation and the degradation products have been determined. GC-MS analyses evidenced the formation of 1-tridecanal, di-n-octylamine, N,N,N-octen-1-yl-dioctylamine, and an unidentified degradation compound, which may have contained a double bond and a carboxylic acid function. The mechanisms of degradation have been discussed on the basis of these identified degradation compounds. The study of the degradation kinetics showed that an increase of tri-n-octylamine concentration in the organic phase is responsible for a decrease of the degradation rate, while an increase in sulfuric acid concentration in the aqueous phase leads to a strong increase in the degradation rate. Full article
(This article belongs to the Special Issue Advances in Hydrometallurgy)
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Open AccessArticle Preparation and Characterization of TiB2-(Supra-Nano-Dual-Phase) High-Entropy Alloy Cermet by Spark Plasma Sintering
Metals 2018, 8(1), 58; https://doi.org/10.3390/met8010058
Received: 29 November 2017 / Revised: 23 December 2017 / Accepted: 9 January 2018 / Published: 17 January 2018
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Abstract
This paper introduces the preparation method and characterization results of TiB2 ceramics with CoCrFeNiAl high-entropy alloy (HEA) as a sintering aid by Spark Plasma Sintering (SPS). Good wettability between HEA and TiB2 was proved by the sessile drop method, indicating promising
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This paper introduces the preparation method and characterization results of TiB2 ceramics with CoCrFeNiAl high-entropy alloy (HEA) as a sintering aid by Spark Plasma Sintering (SPS). Good wettability between HEA and TiB2 was proved by the sessile drop method, indicating promising prospects for this composite. The sintering results showed that the addition of HEA could dramatically promote the sinterability of TiB2. TiB2-5 wt. % HEA dense ceramics prepared at the optimal temperature of 1650 °C showed fine morphology without formation of brittle phases. The liquid phase in the ceramics was highly consistent with the so-called “supra-nano-dual-phase materials (SNDPM)”, with near-ideal strength. This study represents the first time that a ceramic-SNDPM composite has been fabricated since the invention of such structures. Full article
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Open AccessArticle Experimental Study for Improving the Repair of Magnesium–Aluminium Hybrid Parts by Turning Processes
Metals 2018, 8(1), 59; https://doi.org/10.3390/met8010059
Received: 23 November 2017 / Revised: 4 January 2018 / Accepted: 11 January 2018 / Published: 16 January 2018
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Abstract
One of the lightest metallic materials used in the aeronautics, aerospace, and automotive industries, among others, is magnesium, due to its excellent weight/strength ratio. Most parts used in these industries need to be made of materials that are rigid, strong, and lightweight, but
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One of the lightest metallic materials used in the aeronautics, aerospace, and automotive industries, among others, is magnesium, due to its excellent weight/strength ratio. Most parts used in these industries need to be made of materials that are rigid, strong, and lightweight, but sometimes the materials do not simultaneously satisfy all of the properties required. An alternative is to combine two or more materials, giving rise to a hybrid component that can satisfy a wider range of properties. The pieces machined in these industrial fields must satisfy stringent surface roughness requirements that conform to the design specifications. This work shows an experimental study to analyse the surface roughness reached in hybrid components made up of a base of magnesium alloy (UNS M11917) and two inserts of aluminium alloy (UNS A92024) obtained by turning. Its purpose is to determine the influence of the factors and their possible interactions on the response variable, the surface roughness Ra. The study is carried out using a design of experiments (DOE). A product of a full factorial 23 and a block of two factors 3 × 2 was selected. The factors identified as possible sources of variation of the surface roughness are: depth of cut, feed rate, spindle speed, type of tool, location with respect to the specimen (LRS), and location with respect to the insert (LRI). Data were analysed by means of the analysis of variance (ANOVA) method. The main conclusion is the possibility to carry out the repair and maintenance of parts of magnesium–aluminum hybrid components by dry turning; that is, without cutting fluids and, therefore, in the most sustainable way that the process can be carried out. In addition, different combinations of cutting parameters have been identified that allow these operations to be carried out in an efficient manner, reducing mechanization times and, therefore, also the direct and indirect costs associated with them. Full article
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Open AccessArticle Transient Liquid Phase Bonding of Magnesium Alloy AZ31 Using Cu Coatings and Cu Coatings with Sn Interlayers
Metals 2018, 8(1), 60; https://doi.org/10.3390/met8010060
Received: 28 November 2017 / Revised: 27 December 2017 / Accepted: 11 January 2018 / Published: 16 January 2018
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Abstract
Transient liquid phase bonding (TLP) of AZ31 samples has been investigated using Cu coatings and Cu coatings with Sn interlayer. Copper coatings were used for one set of the bonds, and a combination of Cu coatings and Sn interlayer was used for the
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Transient liquid phase bonding (TLP) of AZ31 samples has been investigated using Cu coatings and Cu coatings with Sn interlayer. Copper coatings were used for one set of the bonds, and a combination of Cu coatings and Sn interlayer was used for the other set of bonds. The bonding temperature was fixed at 520 °C, and various bonding times were applied. This study shows that the bonds produced using only Cu coatings have shown weaker bonds compared to the bonds made using Cu coatings and Sn interlayer. The Cu2Mg particles were detected at the joint region of both bonds made by Cu coatings and Cu coatings with Sn interlayer by X-ray diffraction (XRD). However, it has been observed that the joint region was dominated by solid solution which is rich in Mg. Sn interlayer was not contributed to the intermetallic compound (IMC) at the joint region, and therefore it was diffused away through the Mg matrix. Within the joint interface, a slight increase of micro-hardness was observed compared to Mg base metal alloy. This was attributed to the formation and presence of IMC’s within the joint region. It was noticed that the presence of the Sn interlayer improved the joint strength by reducing the pores at the joint region. Pores were clearly observed for those bonds made using Cu coatings—especially for region where the fracture occurs; this was accomplished by scanning electron microscope (SEM). Full article
(This article belongs to the Special Issue Diffusion Bonding and Brazing of Advanced Materials)
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Open AccessArticle Synthesis and Thermoelectric Properties of Ni-Doped ZrCoSb Half-Heusler Compounds
Metals 2018, 8(1), 61; https://doi.org/10.3390/met8010061
Received: 28 December 2017 / Revised: 11 January 2018 / Accepted: 11 January 2018 / Published: 17 January 2018
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Abstract
The Ni-doped ZrCo1−xNixSb half-Heusler compounds were prepared by arc-melting and spark plasma sintering technology. X-ray diffraction analysis results showed that all samples were crystallized in a half-Heusler phase. Thermoelectric properties of ZrCo1−xNixSb compounds
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The Ni-doped ZrCo1−xNixSb half-Heusler compounds were prepared by arc-melting and spark plasma sintering technology. X-ray diffraction analysis results showed that all samples were crystallized in a half-Heusler phase. Thermoelectric properties of ZrCo1−xNixSb compounds were measured from room temperature to 850 K. The electrical conductivity and the absolute value of Seebeck coefficient increased with the Ni-doping content increasing due to the Ni substitution at Co. sites. The lattice thermal conductivity of ZrCo1−xNixSb samples was depressed dramatically because of the acoustic phonon scattering and point defect scattering. The figure of merit of ZrCo1−xNixSb compounds was improved due to the decreased thermal conductivity and improved power factor. The maximum ZT value of 0.24 was achieved for ZrCo0.92Ni0.08Sb sample at 850 K. Full article
(This article belongs to the Special Issue Heusler Compounds)
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