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Metals, Volume 10, Issue 2 (February 2020) – 141 articles

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Cover Story (view full-size image) The unidirectional cellular structure (UniPore,) with long and uniform unidirectional cells, was [...] Read more.
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Open AccessArticle
FAST-forge of Titanium Alloy Swarf: A Solid-State Closed-Loop Recycling Approach for Aerospace Machining Waste
Metals 2020, 10(2), 296; https://doi.org/10.3390/met10020296 - 24 Feb 2020
Viewed by 204
Abstract
Titanium alloys have excellent properties, but components are very expensive due to the high levels of processing required, such as vacuum melting, multi-stage forging, and machining. As a result, forged titanium alloy components are largely exclusive to the aerospace industry, where a high [...] Read more.
Titanium alloys have excellent properties, but components are very expensive due to the high levels of processing required, such as vacuum melting, multi-stage forging, and machining. As a result, forged titanium alloy components are largely exclusive to the aerospace industry, where a high strength-to-weight ratio, corrosion resistance, and excellent fatigue resistance are essential. However, a typical buy-to-fly ratio for such components is approximately 9:1, as much of the forged billet is machined to swarf. The quantity of waste titanium alloy swarf generated is increasing as aircraft orders, and the titanium components contained within them, are increasing. In this paper, waste swarf material has been recycled using the two-step solid-state FAST-forge process, which utilizes field assisted sintering technology (FAST) followed by hot forging. Cleaned Ti-6Al-4V swarf was fully consolidated using the FAST process at sub-transus and super-transus temperatures, followed by hot forging at sub-transus temperatures at different strain rates. It was demonstrated that swarf-derived Ti-6Al-4V FAST billets have equivalent hot forging flow behaviour and resultant microstructures when directly compared to equivalently processed conventional expensive hydride–dehydride powder, and previously reported Kroll-derived melt-wrought material. This demonstrates that titanium swarf is a good quality feedstock for downstream processing. Additionally, FAST-forge is a viable processing route for the closed-loop recycling of machining waste for next-generation components in vehicles and non-aerospace applications, which is game changing for the economics of titanium alloy components. Full article
(This article belongs to the Special Issue Towards the Development of Affordable Titanium Alloy Components)
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Open AccessEditorial
Refining and Casting of Steel
Metals 2020, 10(2), 295; https://doi.org/10.3390/met10020295 - 24 Feb 2020
Viewed by 168
Abstract
Steel was the most requested material all over the world during the past fast technically evolving centuries [...] Full article
(This article belongs to the Special Issue Refining and Casting of Steel)
Open AccessArticle
The Interdependence of the Degree of Precipitation and Dislocation Density during the Thermomechanical Treatment of Microalloyed Niobium Steel
Metals 2020, 10(2), 294; https://doi.org/10.3390/met10020294 - 24 Feb 2020
Viewed by 129
Abstract
In this paper, thermomechanical processing of niobium microalloyed steel was performed with the purpose of determining the interaction between niobium precipitates and dislocations, as well as determining the influence of the temperature of final deformation on the degree of precipitation and dislocation density. [...] Read more.
In this paper, thermomechanical processing of niobium microalloyed steel was performed with the purpose of determining the interaction between niobium precipitates and dislocations, as well as determining the influence of the temperature of final deformation on the degree of precipitation and dislocation density. Two variants of thermomechanical processing with different final rolling temperatures were carried out. Samples were studied using electrochemical isolation with an atomic absorption spectrometer, transmission electron microscopy, X-ray diffraction analysis, and universal tensile testing with a thermographic camera. The results show that the increase in the density of dislocations before the onset of intense precipitation is insignificant because the recrystallization process takes place simultaneously. It increases with the onset of strain-induced precipitation. In this paper, it is shown that niobium precipitates determine the density of dislocations. The appearance of Lüders bands was noticed as a consequence of the interaction between niobium precipitates and dislocations during the subsequent cold deformation. In both variants of the industrial process performed on the cold deformed strip, Lüders bands appeared. Full article
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Open AccessFeature PaperArticle
Selective Copper Recovery by Acid Leaching from Printed Circuit Board Waste Sludge
Metals 2020, 10(2), 293; https://doi.org/10.3390/met10020293 - 23 Feb 2020
Viewed by 252
Abstract
The most challenging issue associated with recycling the sludge generated from printed circuit boards (PCBs) is the separation of copper (Cu) from iron (Fe), using multi-stage leaching, or adding oxidizing and precipitating agents. Herein we investigated simple acid leaching to effectively extract copper [...] Read more.
The most challenging issue associated with recycling the sludge generated from printed circuit boards (PCBs) is the separation of copper (Cu) from iron (Fe), using multi-stage leaching, or adding oxidizing and precipitating agents. Herein we investigated simple acid leaching to effectively extract copper and limit iron dissolution. Selective copper leaching was achieved with all the acids studied, including HCl, HNO3, and H2SO4. The lower concentration of acid solutions resulted in a larger difference in leachabilities between Cu and Fe. Among three leachates, the H2SO4 solution performed effectively on the selective leaching of Cu and Fe. Adjusting the pulp density to 4% and the H2SO4 concentration at ~0.2 M, accomplished ~95% Cu leaching and reduced the Fe extraction to less than 5%. Kinetic studies revealed that Cu leaching followed the ash diffusion-controlled mechanism. Aactivation energy (Ea) of 9.8 kJ/mol was determined for the first 10 min of leaching. Further, leaching up to 60 min corresponded to a mixed control model, increasing the Ea to 20.9 kJ/mol. The change in the control model with regard to the two leaching stages can be attributed to the Cu hydroxide and metal phases present in the original sample. A simple, economically attractive H2SO4 acid leaching process was demonstrated, recovering Cu efficiently and selectively from PCBs waste sludge under moderate conditions. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
Open AccessArticle
Effect of SLM Processing Parameters on Microstructures and Mechanical Properties of Al0.5CoCrFeNi High Entropy Alloys
Metals 2020, 10(2), 292; https://doi.org/10.3390/met10020292 - 23 Feb 2020
Viewed by 169
Abstract
Selective laser melting (SLM) to fabricate Al0.5CoCrFeNi high entropy alloys with pre-mixed powders was studied in this paper. The influences of process parameters including laser power, scanning speed, and hatch spacing on the relative density of high-entropy alloys (HEAs) were investigated. [...] Read more.
Selective laser melting (SLM) to fabricate Al0.5CoCrFeNi high entropy alloys with pre-mixed powders was studied in this paper. The influences of process parameters including laser power, scanning speed, and hatch spacing on the relative density of high-entropy alloys (HEAs) were investigated. A relative density of 99.92% can be achieved by optimizing the SLM process parameters with laser power 320 W, scanning speed 800 mm/s, and hatch spacing of 60 μm, respectively. Moreover, the microstructure of the HEAs was also studied using scanning electron microscopy (SEM) and x-ray diffraction (XRD). It was found that the microstructure of the HEAs was only composed of face-centered cubic and body-centered cubic phases, without complex intermetallic compounds. The mechanical properties of the HEAs were also characterized. At ambient temperature, the alloys had a high yield strength of about 609 MPa, tensile strength about 878 MPa, and hardness about 270 HV. Through a comparison with the corresponding alloys fabricated by vacuum induction melting, it can be concluded that the high entropy alloys fabricated by SLM had fine microstructures and improved mechanical properties. Full article
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Open AccessArticle
The Elusive Thomson Effect in Thermoelectric Devices. Experimental Investigation from 363 K to 213 K on Various Peltier Modules
Metals 2020, 10(2), 291; https://doi.org/10.3390/met10020291 - 23 Feb 2020
Viewed by 174
Abstract
At steady state, in the governing equation of one-stage thermoelectric cooler, the heat resulting from Fourier conduction is balanced by heat generation due to the Joule and Thomson effects inside semiconductors. Since the heat flux observed at the junction of a semiconductor, r [...] Read more.
At steady state, in the governing equation of one-stage thermoelectric cooler, the heat resulting from Fourier conduction is balanced by heat generation due to the Joule and Thomson effects inside semiconductors. Since the heat flux observed at the junction of a semiconductor, r pair includes the Peltier effect and the Fourier heat flux caused by both the aforementioned contributions, the Thomson effect is easily masked by the Joule heat, which makes it elusive. With the aim of highlighting the contribution of the Thomson effect, measurements were carried out in the temperature range from 363 K to 213 K on different Peltier modules. The temperature dependence of the Seebeck and Thomson coefficients was evaluated as well as the electrical resistivity, and thermal conductivity of the Peltier modules examined. The results obtained show that the temperature dependence of the thermoelectric properties can reduce the cooling capacity of the Peltier module compared to what is declared in the technical datasheets of the commercial devices. The analyses allow us to conclude that an increase in the Thomson effect could have a positive effect on the performance of the Peltier only if it were possible to reduce the Joule contribution simultaneously. Full article
(This article belongs to the Special Issue Thermoelectric Compounds: Processing, Properties and Applications)
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Open AccessArticle
Surface Quality and Free Energy Evaluation of s275 Steel by Shot Blasting, Abrasive Water Jet Texturing and Laser Surface Texturing
Metals 2020, 10(2), 290; https://doi.org/10.3390/met10020290 - 22 Feb 2020
Viewed by 212
Abstract
Surface modification by different technologies prior to joining operations or improving tribological properties is a point of great interest. Improving surface activation by increasing the roughness of the metal is a relationship that is becoming more defined. In turn, an increase in surface [...] Read more.
Surface modification by different technologies prior to joining operations or improving tribological properties is a point of great interest. Improving surface activation by increasing the roughness of the metal is a relationship that is becoming more defined. In turn, an increase in surface wettability by evaluating contact angles indicates surface activation by obtaining a high surface free energy. Technologies such as shot blasting and laser surface texturing (LST) have generated several scientific studies where they have identified the influence of parameters on the formation of rough surfaces with defined patterns. However, the application of abrasive water jet texturing (AWJT) has been little studied as an alternative. This article compares these technologies in the texturing of a carbon steel s275 in order to identify the relationship between surface quality and surface activation. It has been determined that AWJT produces the highest Rt values close to 64 µm with a cross feed of 0.45 mm and a traverse speed of 5000 mm/min. Furthermore, LST obtains the best values of free surface energy by combining a power of 20 W with a frequency of 20 kHz and a sweeping speed of 10 mm/s. Finally, contour diagrams have been obtained which relate these variables to the texturing parameters. Full article
(This article belongs to the Special Issue Surface Modification Technology in Metals)
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Open AccessArticle
Influence of Elastomer Layers in the Quality of Aluminum Parts on Finishing Operations
Metals 2020, 10(2), 289; https://doi.org/10.3390/met10020289 - 22 Feb 2020
Viewed by 198
Abstract
In finishing processes, the quality of aluminum parts is mostly influenced by static and dynamic phenomena. Different solutions have been studied toward a stable milling process attainment. However, the improvements obtained with the tuning of process parameters are limited by the system stiffness [...] Read more.
In finishing processes, the quality of aluminum parts is mostly influenced by static and dynamic phenomena. Different solutions have been studied toward a stable milling process attainment. However, the improvements obtained with the tuning of process parameters are limited by the system stiffness and external dampers devices interfere with the machining process. To deal with this challenge, this work analyzes the suitability of elastomer layers as passive damping elements directly located under the part to be machined. Thus, exploiting the sealing properties of nitrile butadiene rubber (NBR), a suitable flexible vacuum fixture is developed, enabling a proper implementation in the manufacturing process. Two different compounds are characterized under axial compression and under finishing operations. The compression tests present the effect of the feed rate and the strain accumulative effect in the fixture compressive behavior. Despite the higher strain variability of the softer rubber, different milling process parameters, such as the tool feed rate, can lead to a similar compressive behavior of the fixture regardless the elastomer hardness. On the other hand, the characterization of these flexible fixtures is completed over AA2024 floor milling of rigid parts and compared with the use of a rigid part clamping. These results show that, as the cutting speed and the feed rate increases, due to the strain evolution of the rubber, the part quality obtained tend to equalize between the flexible and the rigid clamping of the workpiece. Due to the versatility of the NBR for clamping different part geometries without new fixture redesigns, this leads to a competitive advantage of these flexible solutions against the classic rigid vacuum fixtures. Finally, a model to predict the grooving forces with a bull-nose end mill regardless of the stiffness of the part support is proposed and validated for the working range. Full article
(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)
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Open AccessReview
The Challenge of Digitalization in the Steel Sector
Metals 2020, 10(2), 288; https://doi.org/10.3390/met10020288 (registering DOI) - 21 Feb 2020
Viewed by 276
Abstract
Digitalization represents a paramount process started some decades ago, but which received a strong acceleration by Industry 4.0 and now directly impacts all the process and manufacturing sectors. It is expected to allow the European industry to increase its production efficiency and its [...] Read more.
Digitalization represents a paramount process started some decades ago, but which received a strong acceleration by Industry 4.0 and now directly impacts all the process and manufacturing sectors. It is expected to allow the European industry to increase its production efficiency and its sustainability. In particular, in the energy-intensive industries, such as the steel industry, digitalization concerns the application of the related technologies to the production processes, focusing on two main often overlapping directions: Advanced tools for the optimization of the production chain and specific technologies for low-carbon and sustainable production. Furthermore, the rapid evolution of the technologies in the steel sector require the continuous update of the skills of the industrial workforce. The present review paper, resulting from a recent study developed inside a Blueprint European project, introduces the context of digitalization and some important definitions in both the European industry and the European iron and steel sector. The current technological transformation is depicted, and the main developments funded by European Research Programs are analyzed. Moreover, the impact of digitalization on the steel industry workforce are considered together with the foreseen economic developments. Full article
(This article belongs to the Special Issue Challenges and Prospects of Steelmaking Towards the Year 2050)
Open AccessArticle
Multi-Objective Optimization of Intermediate Roll Profile for a 6-High Cold Rolling Mill
Metals 2020, 10(2), 287; https://doi.org/10.3390/met10020287 - 21 Feb 2020
Viewed by 208
Abstract
The multi-objective optimization of the SmartCrown intermediate roll profile for a cold rolling mill was proposed in this paper in order to improve the strip flatness quality. A coupling model of roll profile and strip flatness was established, and the roll gap profile, [...] Read more.
The multi-objective optimization of the SmartCrown intermediate roll profile for a cold rolling mill was proposed in this paper in order to improve the strip flatness quality. A coupling model of roll profile and strip flatness was established, and the roll gap profile, roll gap crown adjustment range, rolls contact pressure, and strip flatness under different intermediate roll profile parameters were calculated based on the coupling model. The results showed that the roll gap crown adjustment range and rolls contact pressure difference increased with increasing roll profile parameters. The roll profile parameters were multi-optimized based on the non-dominated sorting genetic algorithm II (NSGA-II). The minimum rolls contact pressure difference and maximum roll gap crown adjustment range were taken as the objective function of multi-objective optimization. The optimal roll profile parameters were applied to a six-high five stand tandem cold rolling mills, which improved the flatness quality of the DP780 steel strip. Full article
Open AccessArticle
Metallurgical Characterization of the Interfaces in Steel Plates Clad with Austenitic Steel or High Ni Alloys by Hot Rolling
Metals 2020, 10(2), 286; https://doi.org/10.3390/met10020286 - 21 Feb 2020
Viewed by 160
Abstract
An integrated experimental-theoretical approach to the metallurgical characterization of the interfaces in steel plates clad by hot rolling is proposed. Three different couplings of materials have been studied: ASTM A 515 Gr.60 low carbon steel clad with austenitic stainless steel AISI 304L; extra [...] Read more.
An integrated experimental-theoretical approach to the metallurgical characterization of the interfaces in steel plates clad by hot rolling is proposed. Three different couplings of materials have been studied: ASTM A 515 Gr.60 low carbon steel clad with austenitic stainless steel AISI 304L; extra low carbon steel ASTM A283 clad with high Ni content Alloy 59; and, low carbon steel AISI 1010 clad with Cu-Ni Monel 400. Experimental investigations, which are addressed to analyse the microstructural changes near the interfaces and identify the present phases, have been carried out through scanning electron microscopy (SEM) observations, microanalytical measurements by energy dispersive spectroscopy (EDS), and Vickers microhardness tests. In all of the cases examined, the zones that are affected by detrimental microstructural changes results in being considerably less thick than the overall cladding layer. Simulations that are based on theoretical diffusion modelling have been integrated to the experimental characterization by introducing a cladding parameter that acts on the diffusion bonding efficiency, in order to evaluate the effects of process temperature and time variations on diffusion bonding efficiency and stability. In particular, this analytical investigation has shown how the shorter is the duration of the diffusion transient and the higher the temperature, the lower results the sensitivity of the diffusion processes to temperature fluctuations. Full article
(This article belongs to the Special Issue Clad Metals: Fabrication, Properties and Applications)
Open AccessArticle
Effects of Microstructure, Mechanical and Physical Properties on Machinability of Graphite Cast Irons
Metals 2020, 10(2), 285; https://doi.org/10.3390/met10020285 - 21 Feb 2020
Viewed by 164
Abstract
Flake (FGI) and spheroidal (SGI) graphite cast irons are often used to produce workpieces, which often need to be machined. Machinability differences under various machining methods are the basis for choosing machining equipment and technology. In this work, FGI and SGI were used [...] Read more.
Flake (FGI) and spheroidal (SGI) graphite cast irons are often used to produce workpieces, which often need to be machined. Machinability differences under various machining methods are the basis for choosing machining equipment and technology. In this work, FGI and SGI were used to produce tractor front brackets, and the machinability of both materials under turning and drilling processes was compared. The machinability (turning and drilling ability) has been evaluated in terms of machining load, chips shape, surface roughness, and tool temperature. The influence of materials microstructure and thermal conductivity on the machinability was analyzed. In the turning process, the cutting force and its standard deviation of the FGI were larger than the SGI due to the higher volume fraction of pearlite. The surface roughness was similar in both materials. In the drilling process, the even action of the friction and cutting force on the bit turned into similar drilling loads for both materials. Higher friction and lower thermal conductivity caused a higher bit temperature in SGI drilling compared to FGI. The chip breaking was worse in SGI drilling, where the longer chips scratched the internal surface of the holes, resulting in the higher surface roughness. Full article
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Open AccessArticle
PbO-SiO2 Based Glass Coating of PbI2 Doped PbTe
Metals 2020, 10(2), 284; https://doi.org/10.3390/met10020284 - 21 Feb 2020
Viewed by 134
Abstract
Thermoelectrics is one promising way of increasing the efficiency of machines and devices by reusing some of the waste heat produced. One obstacle for commercialization is the need to coat the materials to prevent sublimation and oxidation of the thermoelectric materials. Such coatings [...] Read more.
Thermoelectrics is one promising way of increasing the efficiency of machines and devices by reusing some of the waste heat produced. One obstacle for commercialization is the need to coat the materials to prevent sublimation and oxidation of the thermoelectric materials. Such coatings were designed for PbI2 doped PbTe using a (SiO2)0.68(PbO)0.3(B2O3)0.01(Na2O)0.01 based glass designed for operation at 500 °C. In this research various conditions of the coating process were examined. The effect of the atmosphere on the bonding and densification of the coating was studied using argon, vacuum and air. From the three air shows, the best bonding characteristics were from a better flow of glass and increased bonding between the oxidized PbTe layer and glass. This also created a PbO rich glass in the interface between the glass and the PbTe sample. The effect of 0, 3, and 6 wt. % NaCl additive to the solution was tested and showed that NaCl achieves better coverage due to high green body density, reaction of NaCl with the glass and removal of remaining CO2 from the glass in the form of decomposing Na2CO3. In addition, when testing the time and temperature, it was shown that the temperature of 520 °C was the minimum needed for high densification of the glass, but a duration shorter than 30 min did not allow for bonding of the glass to the substrate despite adequate densification. Finely, to obtain a well bonded coating with full coverage over the sample, the glass was coated with 6% NaCl in air at 520 °C for 30 min. Full article
(This article belongs to the Special Issue Thermoelectric Compounds: Processing, Properties and Applications)
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Open AccessArticle
Ab Initio Calculations on Elastic Properties of IF Steel Matrix Phase at High Temperature Based on Lattice Expansion Theory
Metals 2020, 10(2), 283; https://doi.org/10.3390/met10020283 - 21 Feb 2020
Viewed by 161
Abstract
Elucidating the evolution law of the elastic properties of the matrix phase is of great significance for the control of steel properties and quality during continuous casting and subsequent heat treatment. In this paper, thermal expansion experiments and ab initio calculations are used [...] Read more.
Elucidating the evolution law of the elastic properties of the matrix phase is of great significance for the control of steel properties and quality during continuous casting and subsequent heat treatment. In this paper, thermal expansion experiments and ab initio calculations are used to study the elastic properties of the interstitial free (IF) steel matrix phase in different magnetic states and crystal structures. The results show that the bulk modulus B and the tetragonal shear elastic constant C’ for the entire temperature range decrease with increasing temperature, but C44 is the opposite. While from paramagnetic (PM) to ferromagnetic (FM) state, C’(C44) have changed ~188% (~27%), B increases by ~55% during the crystal structure change (fcc→bcc). With the FM to PM state, the Zener anisotropy parameter increases sharply, and Young’s modulus decreases significantly in the [001] direction; the maximum difference is ~76 GPa. The evolution rate of average Young’s modulus in single bcc-phase FM (fcc-phase PM) range reaches ~5.5(~5.6) × 10−2 GPa K−1. The research provides an effective method for ab initio calculation of the elastic properties of interstitial free and ultra-low carbon steels at high temperature, also furnishing a basis for the application of ab initio calculations to the high temperature performance of steel materials. Full article
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Open AccessArticle
Influence of Martensite Deformation on Cu Precipitation Strengthening
Metals 2020, 10(2), 282; https://doi.org/10.3390/met10020282 - 21 Feb 2020
Viewed by 136
Abstract
Cu precipitation strengthening was compared in steels after treatments with and without cold rolling. A 0.2% C steel containing up to 1.5% Cu was quenched and tempered. Cu precipitation took place during tempering and increased its yield strength (YS). Quenched and tempered samples [...] Read more.
Cu precipitation strengthening was compared in steels after treatments with and without cold rolling. A 0.2% C steel containing up to 1.5% Cu was quenched and tempered. Cu precipitation took place during tempering and increased its yield strength (YS). Quenched and tempered samples were compared with samples where cold rolling was performed between quenching and tempering. They exhibited significantly different mechanical properties. In addition, Cu alloying influenced the properties of each group of samples in different ways. The quenched and tempered samples exhibited behavior that is typical of precipitation hardening. Cu caused yield strength to increase with tempering temperature and time. The cold rolling of martensite reduced the maximal Cu-related strengthening and also eliminated its time and temperature dependence. Full article
Open AccessFeature PaperReview
Processing and Properties of Reversion-Treated Austenitic Stainless Steels
Metals 2020, 10(2), 281; https://doi.org/10.3390/met10020281 - 21 Feb 2020
Viewed by 136
Abstract
Strength properties of annealed austenitic stainless steels are relatively low and therefore improvements are desired for constructional applications. The reversion of deformation induced martensite to fine-grained austenite has been found to be an efficient method to increase significantly the yield strength of metastable [...] Read more.
Strength properties of annealed austenitic stainless steels are relatively low and therefore improvements are desired for constructional applications. The reversion of deformation induced martensite to fine-grained austenite has been found to be an efficient method to increase significantly the yield strength of metastable austenitic stainless steels without impairing much their ductility. Research has been conducted during thirty years in many research groups so that the features of the reversion process and enhanced properties are reported in numerous papers. This review covers the main variables and phenomena during the reversion processing and lists the static and dynamic mechanical properties obtained in laboratory experiments, highlighting them to exceed those of temper rolled sheets. Moreover, formability, weldability and corrosion resistant aspects are discussed and finally the advantage of refined grain structure for medical applications is stated. The reversion process has been utilized industrially in a very limited extent, but apparently, it could provide a feasible processing route for strengthened austenitic stainless steels. Full article
(This article belongs to the Special Issue Manufacturing and Application of Stainless Steels)
Open AccessArticle
Effects of Positions and Angulations of Titanium Dental Implants in Biomechanical Performances in the All-on-Four Treatment: 3D Numerical and Strain Gauge Methods
Metals 2020, 10(2), 280; https://doi.org/10.3390/met10020280 - 21 Feb 2020
Viewed by 198
Abstract
In finite element (FE) simulations, the peak bone stresses were higher when loading with a cantilever extension (CE) than when loading without a CE by 33–49% in the cortical bone. In the in vitro experiments, the highest values of principal strain were all [...] Read more.
In finite element (FE) simulations, the peak bone stresses were higher when loading with a cantilever extension (CE) than when loading without a CE by 33–49% in the cortical bone. In the in vitro experiments, the highest values of principal strain were all within the range of the minimum principal strain, and those peak bone strains were 40–58% greater when loading with a CE than when loading without a CE (p < 0.001). This study investigated how varying the implanted position and angulation of anterior implants in the All-on-Four treatment influenced the biomechanical environment in the alveolar bone around the dental implants. Ten numerical simulations of FE models and three in vitro samples of All-on-Four treatment of dental implants were created to investigate the effects of altering the implanted position and angulation type of anterior implants. A single load of 100 N was applied in the molar region in the presence or absence of a CE of the denture. The 3D FE simulations analyzed the von-Mises stresses in the surrounding cortical bone and trabecular bone. For the in vitro tests, the principal bone strains were recorded by rosette strain gauges and statistically evaluated using the Mann–Whitney U test and the Kruskal–Wallis test. Loading in the presence of a CE of the denture induced the highest bone stress and strain, which were 53–97% greater in the FE simulation and 68–140% in the in vitro experiments (p < 0.008) than when loading without a CE. The bone stresses in the FE models of various implanted positions and angulation types of anterior implants were similar to those in the model of a typical All-on-Four treatment. In vitro tests revealed that the bone strains were significantly higher in the samples with various angulation types of anterior implants (p < 0.008). In the All-on-Four treatment of dental implants, the bone stress and strain were higher when the load was applied to the CE of dentures. Altering the position or angulation of the anterior dental implant in the All-on-Four treatment has no benefit in relieving the stress and strain of the bone around the dental implant. Full article
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Open AccessReview
Research Status and Progress of Welding Technologies for Molybdenum and Molybdenum Alloys
Metals 2020, 10(2), 279; https://doi.org/10.3390/met10020279 - 20 Feb 2020
Viewed by 160
Abstract
Owing to its potential application prospect in novel accident tolerant fuel, molybdenum alloys and their welding technologies have gained great importance in recent years. The challenges of welding molybdenum alloys come from two aspects: one is related to its powder metallurgy manufacturing process, [...] Read more.
Owing to its potential application prospect in novel accident tolerant fuel, molybdenum alloys and their welding technologies have gained great importance in recent years. The challenges of welding molybdenum alloys come from two aspects: one is related to its powder metallurgy manufacturing process, and the other is its inherent characteristics of refractory metal. The welding of powder metallurgy materials has been associated with issues such as porosity, contamination, and inclusions, at levels which tend to degrade the service performances of a welded joint. Refractory metals usually present poor weldability due to embrittlement of the fusion zone as a result of impurities segregation and the grain coarsening in the heat-affected zone. A critical review of the current state of the art of welding Mo alloys components is presented. The advantages and disadvantages of the various methods, i.e., electron-beam welding (EBW), tungsten-arc inert gas (TIG) welding, laser welding (LW), electric resistance welding (ERW), and brazing and friction welding (FW) in joining Mo and Mo alloys, are discussed with a view to imagine future directions. This review suggests that more attention should be paid to high energy density laser welding and the mechanism and technology of welding Mo alloys under hyperbaric environment. Full article
(This article belongs to the Special Issue Technology of Welding and Joining)
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Open AccessArticle
CMT-Based Wire Arc Additive Manufacturing Using 316L Stainless Steel: Effect of Heat Accumulation on the Multi-Layer Deposits
Metals 2020, 10(2), 278; https://doi.org/10.3390/met10020278 - 20 Feb 2020
Viewed by 170
Abstract
CMT welding sources are garnering attention as alternative heat sources for wire arc additive manufacturing because of their low-heat input. A comprehensive experimental and numerical study on the multi-layer deposition of STS316L was performed to investigate effect of heat accumulation during the deposition. [...] Read more.
CMT welding sources are garnering attention as alternative heat sources for wire arc additive manufacturing because of their low-heat input. A comprehensive experimental and numerical study on the multi-layer deposition of STS316L was performed to investigate effect of heat accumulation during the deposition. The numerical model which is appropriate for WAMM was developed considering the characteristics of the CMT heat source for the first time. Using a high-speed camera, the transient behavior of the CMT arc was investigated, and applied to the heat source of the numerical model. The model was then used to analyze 10-layered deposits of STS316L, fabricated using CMT-based WAAM. During deposition, the temperature is measured using a pyrometer to analyze the microstructure, after which the cooling rate of each layer is estimated. The measured and simulated SDAS were compared. Based on the comparison, a guideline for the equation regarding the SDAS size and cooling rate was suggested. Full article
Open AccessArticle
Mechanical Properties, Thermal Stability and Microstructures of W-Re-ZrC Alloys Fabricated by Spark Plasma Sintering
Metals 2020, 10(2), 277; https://doi.org/10.3390/met10020277 - 20 Feb 2020
Viewed by 149
Abstract
Tungsten materials, used as friction stir welding tools, undergo severe plastic deformation and even collapse at high operating temperatures. In order to improve the low-temperature toughness and high-temperature strength, W-10wt.%Re-0.5wt.%ZrC alloys were processed by high-energy ball milling and subsequent spark plasma sintering. Single [...] Read more.
Tungsten materials, used as friction stir welding tools, undergo severe plastic deformation and even collapse at high operating temperatures. In order to improve the low-temperature toughness and high-temperature strength, W-10wt.%Re-0.5wt.%ZrC alloys were processed by high-energy ball milling and subsequent spark plasma sintering. Single solid-solution W-Re powders with typical body-centered cubic structures were achieved when the milling time increases to 50 h. The microhardness, tensile properties, thermal stability and microstructures of this sintered W-10wt.%Re-0.5wt.%ZrC alloys were investigated. Synergetic effects of the solute Re and nanosized dispersion particles induce improvements in low-temperature toughness and high-temperature strength. The alloy suffers ductile fracture at 300 °C, which is about 400 °C and 300 °C lower than that of the spark plasma sintered pure W and W-0.5wt.%ZrC, respectively. Besides, this W-10wt.%Re-0.5wt.%ZrC has a high ultimate tensile strength of 818 MPa and uniform elongation of ~ 8.1% at 300 °C. Moreover, the microstructures and hardness remain stable even after 1500 °C anneal. Based on a detailed microstructure analysis, the mechanisms for the enhanced strength, low-temperature ductility and high thermal stability are proposed and discussed. Grain boundary mobility is impeded by the kinetics constraint through dispersed particles pinning and solute Re atoms dragging, which leads to improved thermal stability. The formation of Zr-C-O particles is most probably attributed to ZrC particles capturing and interacting with impurity oxygen during sintering. Full article
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Open AccessArticle
A Comprehensive Study into the Boltless Connections of Racking Systems
Metals 2020, 10(2), 276; https://doi.org/10.3390/met10020276 - 20 Feb 2020
Viewed by 144
Abstract
In practice, structures of pallet racks are characterized by very wide options of beam-to-column connections. The up to date part of the standard Eurocode 3 considers details for the design of connections. However, experimental determination of the joint properties in steel pallet racks [...] Read more.
In practice, structures of pallet racks are characterized by very wide options of beam-to-column connections. The up to date part of the standard Eurocode 3 considers details for the design of connections. However, experimental determination of the joint properties in steel pallet racks is the most reliable process, since it takes into account an inability to develop a general analytical model for the design of these connections. In this paper, a test procedure for the behavior of beam-to-column connections is presented and the results are analyzed according to the procedure defined in the relevant design codes. With aim to avoid expensive experiments to determine structural properties of different types of connections, a polynomial model and a corresponding numerical model were developed to be used for simulating the experiment. After verification, the developed analytical and numerical model can be applied for investigation of various combinations of beam-to-column connections. Full article
Open AccessArticle
Evolution of Inclusions in Steelmaking Process of Rare Earth Steels Containing Arsenic with Alumina Crucibles
Metals 2020, 10(2), 275; https://doi.org/10.3390/met10020275 - 20 Feb 2020
Viewed by 146
Abstract
In order to determine strategies for removing arsenic from rare earth arsenic-containing steels, the evolution of inclusions in the whole steelmaking process with alumina crucibles was investigated. It has been proven that adding lanthanum has a significant effect on both the existing state [...] Read more.
In order to determine strategies for removing arsenic from rare earth arsenic-containing steels, the evolution of inclusions in the whole steelmaking process with alumina crucibles was investigated. It has been proven that adding lanthanum has a significant effect on both the existing state and content of arsenic in steel. The content of arsenic steeply decreased after adding 0.148% lanthanum by generating La–S–As inclusions. The addition of 0.054% lanthanum did not dramatically affect the content of arsenic. Both 0.148% and 0.054% additions of lanthanum modified the existing Si–Mn–Al–O inclusions, making them first change to La-containing inclusions, and then change back to Si–Mn–Al–O inclusions. During this process, the compositions of inclusions changed from (SiO2–MnO)-rich to Al2O3-rich ones, owing to the reactions between lanthanum and alumina crucibles. The addition of 0.148% lanthanum resulted in a relatively severe reaction with the alumina crucible. This led to the decomposition of a part of the existing La–S–As inclusions and a slight increase in the arsenic content. Therefore, it is noted that choosing an appropriate holding time after adding rare earth elements to molten steel has a significant effect on the arsenic removal and saving the consumption of rare earth elements. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
Open AccessArticle
A New 3D Creep-Fatigue-Elasticity Damage Interaction Diagram Based on the Total Tensile Strain Energy Density Model
Metals 2020, 10(2), 274; https://doi.org/10.3390/met10020274 - 20 Feb 2020
Viewed by 149
Abstract
Fatigue damage, creep damage, and their interactions are the critical factors in degrading the integrity of most high-temperature engineering structures. A reliable creep-fatigue damage interaction diagram is a crucial issue for the design and assessment of high-temperature components used in power plants. In [...] Read more.
Fatigue damage, creep damage, and their interactions are the critical factors in degrading the integrity of most high-temperature engineering structures. A reliable creep-fatigue damage interaction diagram is a crucial issue for the design and assessment of high-temperature components used in power plants. In this paper, a new three-dimensional creep-fatigue-elasticity damage interaction diagram was constructed based on a developed life prediction model for both high-temperature fatigue and creep fatigue. The total tensile strain energy density concept is adopted as a damage parameter for life prediction by using the elastic strain energy density and mean stress concepts. The model was validated by a great deal of data such as P91 steel at 550 °C, Haynes 230 at 850 °C, Alloy 617 at 850 and 950 °C, and Inconel 625 at 815 °C. The estimation values have very high accuracy since nearly all the test data fell into the scatter band of 2.0. Full article
Open AccessArticle
In Situ Measurements for Plastic Zone ahead of Crack Tip and Continuous Strain Variation under Cyclic Loading Using Digital Image Correlation Method
Metals 2020, 10(2), 273; https://doi.org/10.3390/met10020273 - 19 Feb 2020
Viewed by 182
Abstract
Fatigue crack is one of the most common damage forms for aeronautical aluminum alloy. With crack propagation, the strain fields of the whole object surface and plastic zone (PZ) ahead of the crack tip are changing continuously. For most metallic materials, the behavior [...] Read more.
Fatigue crack is one of the most common damage forms for aeronautical aluminum alloy. With crack propagation, the strain fields of the whole object surface and plastic zone (PZ) ahead of the crack tip are changing continuously. For most metallic materials, the behavior of PZ around the crack tip and continuous strain variation play a vital role in crack propagation. In this work, the “continuous” strain information at and in front of the crack tip on the specimen surface was obtained quantitatively and the PZ size ahead of crack tip was in situ measured quantitatively with crack propagation by using the digital image correlation (DIC) method, which overcomes the difficulty for the in situ measurement of mechanical variables. Moreover, the method of specimen preparation was simplified by using a white matt paint with strong adhesion, but also resulted in a higher resolution being shown, even for such a large area. Furthermore, the experimental results of the PZ size from the proposed method had good agreement with the theoretical values, which overcomes the limitation that the conventional approaches only consider the quasi-static crack. Finally, the continuous strain variation behavior was analyzed from the experimental results in detail with the consideration of crack propagation. Full article
Open AccessArticle
Additive Manufacturing with Superduplex Stainless Steel Wire by CMT Process
Metals 2020, 10(2), 272; https://doi.org/10.3390/met10020272 - 19 Feb 2020
Viewed by 175
Abstract
For many years, the oil and gas industry has utilized superduplex stainless steels due to their high strength and excellent corrosion resistance. Wire arc additive manufacturing (WAAM) was used with superduplex filler wire to create walls with different heat input. Due to the [...] Read more.
For many years, the oil and gas industry has utilized superduplex stainless steels due to their high strength and excellent corrosion resistance. Wire arc additive manufacturing (WAAM) was used with superduplex filler wire to create walls with different heat input. Due to the multiple heating and cooling cycles during layer deposition, brittle secondary phases may form such as intermetallic sigma (σ) phase. By inspecting deposited walls within wide range of heat inputs (0.40‒0.87 kJ/mm), no intermetallic phases formed due to low inter-pass temperatures used, together with the high Ni content in the applied wire. Lower mechanical properties were observed with high heat inputs due to low ferrite volume fraction, precipitation of Cr nitrides and formation of secondary austenite. The walls showed good toughness values based on both Charpy V-notch and CTOD (crack tip opening displacement) testing. Full article
Open AccessArticle
Sheet Metal Forming Optimization Methodology for Servo Press Process Control Improvement
Metals 2020, 10(2), 271; https://doi.org/10.3390/met10020271 - 19 Feb 2020
Viewed by 175
Abstract
In sheet metal forming manufacturing operations the use of servo presses is gaining more interest due to the opportunity to improve process performance (quality, productivity, cost reduction, etc.). It is not yet clear how to proceed in the engineering process when this type [...] Read more.
In sheet metal forming manufacturing operations the use of servo presses is gaining more interest due to the opportunity to improve process performance (quality, productivity, cost reduction, etc.). It is not yet clear how to proceed in the engineering process when this type of operating machine is used to achieve the maximum possible potential of this technology. Recently, several press builders have developed gap- and straight-sided metal forming presses adopting the mechanical servo-drive technology. The mechanical servo-drive press offers the flexibility of a hydraulic press with the speed, accuracy and reliability of a mechanical press. Servo drive presses give the opportunity to improve the productivity of process conditions and improve the quality of stamped parts. Forming simulation and numerical optimization can be useful tools to define beforehand the optimal process parameter set-up in terms of servo press downward curve properties. This is done by carrying out a sensitivity analysis of the forming parameters having influence on said curve. The authors have developed a numerical methodology able to analyze the influence factors, for comparison with the degrees of freedom made available by the usage of a servo press, in terms of stroke profile management, to obtain an optimized process parameters combination. Full article
(This article belongs to the Special Issue Analysis and Design of Metal-Forming Processes)
Open AccessReview
Cavitation Peening: A Review
Metals 2020, 10(2), 270; https://doi.org/10.3390/met10020270 - 19 Feb 2020
Viewed by 224
Abstract
The most popular surface modification technology used to enhance the mechanical properties of metallic materials is shot peening. Shot peening improves fatigue life and strength by introducing local plastic deformation pits. However, the pits increase surface roughness, which is a disadvantage for fatigue [...] Read more.
The most popular surface modification technology used to enhance the mechanical properties of metallic materials is shot peening. Shot peening improves fatigue life and strength by introducing local plastic deformation pits. However, the pits increase surface roughness, which is a disadvantage for fatigue properties. Recently, cavitation peening, in which cavitation bubble collapse impacts are used, has been developed as an advanced surface modification technology. The advantage of cavitation peening is the lesser increase in surface roughness compared with shot peening, as no solid collisions occur in cavitation peening. In conventional cavitation peening, cavitation is generated by injecting a high-speed water jet into water. However, cavitation peening is different from water jet peening, in which water column impacts are used. In the present review, to avoid confusing cavitation peening and water jet peening, fundamentals and mechanisms of cavitation peening are described in comparison to water jet peening, and the effects and applications of cavitation peening are reviewed compared with the other peening methods. Full article
(This article belongs to the Special Issue Advanced Surface Modification Technologies)
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Open AccessArticle
Influence of Submerged Entry Nozzle Port Blockage on the Meniscus Fluctuation Considering Various Operational Parameters
Metals 2020, 10(2), 269; https://doi.org/10.3390/met10020269 (registering DOI) - 18 Feb 2020
Viewed by 165
Abstract
The continuous casting process (CCP) is the most vital part of steelmaking. The flow pattern near the submerged entry nozzle (SEN) and mould greatly influence the quality of the slab produced. The present investigation was carried out to gain knowledge regarding the meniscus [...] Read more.
The continuous casting process (CCP) is the most vital part of steelmaking. The flow pattern near the submerged entry nozzle (SEN) and mould greatly influence the quality of the slab produced. The present investigation was carried out to gain knowledge regarding the meniscus fluctuation under different nozzle port blockage conditions by water model experiments. The experiments were carried out to study the effect of no blockage, 25% blockage, 50% blockage, and 75% blockage of the nozzle port on mould-level fluctuations. The result shows that when the liquid flow rate increases, the wave amplitude increases. In these experiments, the average and maximum meniscus fluctuations were measured while changing different variables such as the water flow rate, gas flow rate, and one-side percentage blockage of the SEN port while the other side was fully open. The observation shows that when the port size decreases, the fluid steel mixed from the obstructing side to the open side results in asymmetry. The average and maximum wave amplitude increases with decreasing submergence depth. It was observed that the maximum height of the standing waves in the mould continued rising on the non-blocked side of the SEN. Blockage increases from 25% to 75%, and with 75% blockage of the right side of the SEN port, the mould-level fluctuation at the left side of the mould was extreme, while that of the right side was relatively quiet. Full article
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Open AccessArticle
Study on the Mechanical and Tribological Properties and the Mechanisms of Cr-Free Ni-Based Self-Lubricating Composites at a Wide Temperature Range
Metals 2020, 10(2), 268; https://doi.org/10.3390/met10020268 - 18 Feb 2020
Viewed by 169
Abstract
A Cr-free Ni-based self-lubricating composites with MoS2 and Ag as lubricants were fabricated by the powder metallurgy method. The microstructures were examined. The mechanical properties and tribological behaviors of the composites were evaluated from room temperature to 800 °C. The fractography was [...] Read more.
A Cr-free Ni-based self-lubricating composites with MoS2 and Ag as lubricants were fabricated by the powder metallurgy method. The microstructures were examined. The mechanical properties and tribological behaviors of the composites were evaluated from room temperature to 800 °C. The fractography was observed and the fracture mechanisms were analyzed. The morphologies and the phase compositions of worn surfaces were determined and the wear mechanisms were elaborated. The results indicate that MoS2 did not completely decompose after sintering, and the NiMoAl-MoS2-Ag composite has the best tribological properties (0.22, 1.68 × 10−5) at 800 °C. The main wear mechanisms are micro-ploughing and plastic deformation. The improvement of tribological properties was attributed to the formation of the lubricating film consisting of NiO, Mo oxides, various molybdates, and Ag particles. The reactions resulting in these compositions are proposed. The mechanical properties degrade with the rise of temperature and the addition of lubricants. Both NiMoAl and NiMoAlAg alloys exhibit micro-void accumulation fracture while the composites with MoS2 reveal intergranular fracture. Full article
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Open AccessArticle
Kinetic Models for the in Situ Reaction between Cu-Ti Melt and Graphite
Metals 2020, 10(2), 267; https://doi.org/10.3390/met10020267 - 18 Feb 2020
Viewed by 155
Abstract
The in situ reaction method for preparing metal matrix composites has the advantages of a simple process, good combination of the reinforcing phase and matrix, etc. Based on the mechanism of forming TiCx particles via the dissolution reaction of solid carbon (C) [...] Read more.
The in situ reaction method for preparing metal matrix composites has the advantages of a simple process, good combination of the reinforcing phase and matrix, etc. Based on the mechanism of forming TiCx particles via the dissolution reaction of solid carbon (C) particles in Cu-Ti melt, the kinetic models for C particle dissolution reaction were established. The kinetic models of the dissolution reaction of spherical, cylindrical, and flat C source particles in Cu-Ti melt were deduced, and the expressions of the time for the complete reaction of C source particles of different sizes were obtained. The mathematical relationship between the degree of reaction of C source and the reaction time was deduced by introducing the shape factor. By immersing a cylindrical C rod in a Cu-Ti melt and placing it in a super-gravity field for the dissolution reaction, it was found that the super-gravity field could cause the precipitated TiCx particles to aggregate toward the upper part of the sample under the action of buoyancy. Therefore, the consuming rate of the C rod was significantly accelerated. Based on the flat C source reaction kinetic model, the relationship between the floating speed of TiCx particles in the Cu-Ti melt and the centrifugal velocity (or the coefficient of super-gravity G) was derived. It was proven that, when the centrifugal velocity exceeded a critical value, the super-gravity field could completely avoid the accumulation behavior of TiCx particles on the surface of the C source, thereby speeding up the formation reaction of TiCx. The goal of this study is to better understand and evaluate the generating process of TiCx particles, thus finding possible methods to increase the reaction efficiency Full article
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