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Metals, Volume 10, Issue 7 (July 2020) – 95 articles

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Open AccessArticle
Low Temperature Sealing Process and Properties of Kovar Alloy to DM305 Electronic Glass
Metals 2020, 10(7), 941; https://doi.org/10.3390/met10070941 (registering DOI) - 13 Jul 2020
Abstract
The low temperature sealing of Kovar alloy to DM305 electronic glass was realized by using lead-free glass solder of the Bi2O3-ZnO-B2O3 system in atmospheric environment. The sealing process was optimized by pre-oxidation of Kovar alloy and [...] Read more.
The low temperature sealing of Kovar alloy to DM305 electronic glass was realized by using lead-free glass solder of the Bi2O3-ZnO-B2O3 system in atmospheric environment. The sealing process was optimized by pre-oxidation of Kovar alloy and low temperature founding of flake glass solder. The effects of sealing temperature and holding time on the properties of sealing joint were studied by means of X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), etc. The results showed that the pre-oxidized Kovar alloy and DM305 electronic glass were successfully sealed with flake glass solder at the sealing temperature of 500 °C for 20 min. Meanwhile, the joint interface had no pores, cracks, and other defects, the shear strength was 12.24 MPa, and the leakage rate of air tightness was 8 × 10−9 Pa·m3/s. During the sealing process, element Bi in glass solder diffused into the oxide layer of Kovar alloy and DM305 electronic glass about 1 μm, respectively. Full article
(This article belongs to the Special Issue Technology of Welding and Joining)
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Open AccessArticle
Effect of Welding Parameters on Friction Stir Welded Ti–6Al–4V Joints: Temperature, Microstructure and Mechanical Properties
Metals 2020, 10(7), 940; https://doi.org/10.3390/met10070940 (registering DOI) - 13 Jul 2020
Abstract
In this study, friction stir welding (FSW) of 2-mm-thick Ti–6Al–4V alloy plates was performed using a newly designed friction tool—and the effect of rotation speed and welding speed on microstructure and mechanical properties of the joints were investigated. A simulation model for FSW [...] Read more.
In this study, friction stir welding (FSW) of 2-mm-thick Ti–6Al–4V alloy plates was performed using a newly designed friction tool—and the effect of rotation speed and welding speed on microstructure and mechanical properties of the joints were investigated. A simulation model for FSW temperature field calculation was developed, and the effect of rotation speed and welding speed on the temperature field was investigated by experimental and numeric methods. The results show that the rotation speed has a dominant effect on peak temperature, while welding speed determines the dwell time of the weld exposed to high temperatures. In addition, the influence of process parameters on the microstructure of the joints was investigated using optical and scanning electron microscopy. The results revealed that there was a phase transformation in the stir zone during welding. The final microstructure of the stir zone was fully lamellar (α + β) structure, and the heat affection zone had a bimodal microstructure consisting of prior equiaxed α and lamellar (α + β) structure. Both rotation speed and welding speed affect the grain size of the weld. Lower peak temperature with decreasing spindle speed and/or shorter dwell time with increasing feed rate could produce finer grains in the stir zone of the joints, thereby could lead to higher microhardness value and the tensile strength of the joints. Full article
(This article belongs to the Special Issue Friction Stir Welding Prospective on Light-Alloys Joints)
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Open AccessArticle
Sustainability-Based Optimization of the Rotary Turning of the Hardened Steel
Metals 2020, 10(7), 939; https://doi.org/10.3390/met10070939 (registering DOI) - 12 Jul 2020
Viewed by 206
Abstract
The rotary turning is an effective manufacturing method to machine hardened metals due to longer tool life, higher production rate, and acceptable quality. However, sustainability-based optimization of the rotary turning has not been thoroughly considered because of the huge efforts. This study presents [...] Read more.
The rotary turning is an effective manufacturing method to machine hardened metals due to longer tool life, higher production rate, and acceptable quality. However, sustainability-based optimization of the rotary turning has not been thoroughly considered because of the huge efforts. This study presents an optimization to enhance the energy efficiency (EFR), turning cost (CT), average roughness (Ra), and the operational safety (POS) for the rotary turning of the hardened steel. Four key process parameters considered are the inclined angle (α), depth of cut (ap), feed rate (f), and cutting speed (vc). The improved Kriging (IK) models were used to construct the relations between the parameters and performances. The optimum varied factors were obtained utilizing the neighborhood cultivation genetic algorithm (NCGA). The findings revealed that the performance models are primarily affected by the feed rate, depth of cut, speed, and inclined angle, respectively. The optimal values of the α, ap, f, and vc are 26°, 0.44 mm, 0.37 mm/rev, and 200 mm/min, respectively. The improvements in energy efficiency, average roughness, and cost are 8.91%, 20.00%, and 14.75%, as compared to the initial values. Moreover, the NCGA may perform an efficient operation to obtain the optimal outcomes, as compared to conventional algorithms. Full article
(This article belongs to the Special Issue Optimization and Analysis of Metal Cutting Processes)
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Open AccessArticle
Analysis of Tribological Properties in Disks of AA-5754 and AA-5083 Aluminium Alloys Previously Processed by Equal Channel Angular Pressing and Isothermally Forged
Metals 2020, 10(7), 938; https://doi.org/10.3390/met10070938 (registering DOI) - 11 Jul 2020
Viewed by 173
Abstract
In the present study, the wear behaviour of two aluminium alloys (AA-5754 and AA-5083) is analysed where these have been previously processed by severe plastic deformation (SPD) with equal channel angular pressing (ECAP). In order to achieve the objectives of this study, several [...] Read more.
In the present study, the wear behaviour of two aluminium alloys (AA-5754 and AA-5083) is analysed where these have been previously processed by severe plastic deformation (SPD) with equal channel angular pressing (ECAP). In order to achieve the objectives of this study, several disks made of these alloys are manufactured by isothermal forging from different initial states. The microstructures of the initial materials analysed in this study have different accumulated deformation levels. In order to compare the properties of the nanostructured materials with those which have not been ECAP-processed, several disks with a height of 6 mm and a diameter of 35 mm are manufactured from both aluminium alloys (that is, AA-5754 and AA-5083) isothermally forged at temperatures of 150 and 200 °C, respectively. These thus-manufactured disks are tested under a load of 0.6 kN, which is equivalent to a stress mean value of 18 MPa, and at a rotational speed of 200 rpm. In order to determine the wear values, the disks are weighed at the beginning, at 10,000 revolutions, at 50,000 revolutions and at 100,000 revolutions, and then the volume-loss values are calculated. This study was carried out using specific equipment, which may be considered to have a block-on-ring configuration, developed for testing in-service wear behaviour of mechanical components. From this, the wear coefficients for the two materials at different initial states are obtained. In addition, a comparison is made between the behaviour of the previously ECAP-processed aluminium alloys and those that are non-ECAP-processed. A methodology is proposed to determine wear coefficients for the aluminium alloys under consideration, which may be used to predict the wear behaviour. It is demonstrated that AA-5754 and AA-5083 aluminium alloys improve wear behaviour after the ECAP process compared to that obtained in non-ECAP-processed materials. Full article
(This article belongs to the Special Issue Challenges and Achievements in Metal Forming)
Open AccessArticle
Ageing of Al-Mn-Cu-Be Alloys for Stimulating Precipitation of Icosahedral Quasicrystals
Metals 2020, 10(7), 937; https://doi.org/10.3390/met10070937 (registering DOI) - 11 Jul 2020
Viewed by 183
Abstract
In this work, the ageing of some Al-Mn-Cu-Be alloys was investigated in the temperature range in which predominantly icosahedral quasicrystalline (IQC) precipitates can form. The alloys were cast into a copper mould, directly aged (T5 heat treatment) between 300 and 440 °C for [...] Read more.
In this work, the ageing of some Al-Mn-Cu-Be alloys was investigated in the temperature range in which predominantly icosahedral quasicrystalline (IQC) precipitates can form. The alloys were cast into a copper mould, directly aged (T5 heat treatment) between 300 and 440 °C for different times. Afterwards, they were examined using scanning and transmission electron microscopy, X-ray diffraction and hardness testing. The main aim of the work was to determine the conditions at which a high number density of spherical icosahedral quasicrystalline precipitates can form. The highest number density of IQC precipitates was obtained at 300 °C after prolonged ageing. The spheroidal precipitates had a diameter less than 20 nm. The size of IQC precipitates increased with the increasing temperature, and in addition, decagonal quasicrystalline precipitates appeared. The time to maximum hardness decreased strongly with increasing ageing temperature. The IQC precipitates can form in a fairly broad temperature range in Al-Mn-Cu-Be alloys and that by varying ageing temperature and duration, rather different distributions of precipitates can be obtained. The presence of precipitates caused rather strong aluminium alloys and fast work hardening during initial plastic deformation. Full article
(This article belongs to the Special Issue Structure and Properties of Aluminium Alloys)
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Open AccessArticle
Initial Deformation Behaviors in Lean Duplex Stainless Steel
Metals 2020, 10(7), 936; https://doi.org/10.3390/met10070936 (registering DOI) - 11 Jul 2020
Viewed by 181
Abstract
The deformation behaviors of the austenite phase in lean duplex stainless steels were investigated through uniaxial tension tests with different amounts of deformation. Microstructural analysis showed that in the initial deformation stage the deformation in austenite grains had a predominant effect on the [...] Read more.
The deformation behaviors of the austenite phase in lean duplex stainless steels were investigated through uniaxial tension tests with different amounts of deformation. Microstructural analysis showed that in the initial deformation stage the deformation in austenite grains had a predominant effect on the strain hardening behavior of the LDX-2101 steel. The initial deformation in the austenite grains was found to be mainly accommodated by the formation of stacking faults. As the deformation increased further, mechanical twins were generated by the initial stacking faults and sequentially interacted with dislocations to accommodate the strain. The analysis of dislocation behavior revealed that the deformation twinning process followed the three-layer twin formation mechanism. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
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Open AccessArticle
The Influence of Quench Interruption and Direct Artificial Aging on the Hardening Response in AA6082 during Hot Deformation and In-Die Quenching
Metals 2020, 10(7), 935; https://doi.org/10.3390/met10070935 (registering DOI) - 11 Jul 2020
Viewed by 133
Abstract
The automotive industry is searching for lightweight solutions to meet emission regulations. Development of an integrated hot forming and in-die quenching process will leverage use of age-hardenable aluminum alloys with high specific strength for applications in volume car manufacturing. Quench interruption and direct [...] Read more.
The automotive industry is searching for lightweight solutions to meet emission regulations. Development of an integrated hot forming and in-die quenching process will leverage use of age-hardenable aluminum alloys with high specific strength for applications in volume car manufacturing. Quench interruption and direct artificial aging may reduce the cycle time in a die-quenching process. However, this alters the temperature exposure of the part and results in an altered precipitation and clustering sequence during hardening. To investigate the effect of modified precipitation and clustering on mechanical properties, the process has been simulated by application of a water-cooled compression tool to control the combination of a temperature drop and simultaneous deformation prior to aging. Extruded 4.6 mm thick AA6082 profiles were deformed during different quenching rates and directly transferred to subsequent artificial aging from various temperatures between room temperature and 200 °C. The results indicate insignificant changes of strength and elongation after direct aging from 200 °C compared to specimens cooled to room temperature before aging. Full article
(This article belongs to the Special Issue Selected Papers from LightMat 2019)
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Open AccessReview
Recent Progress in Transient Liquid Phase and Wire Bonding Technologies for Power Electronics
Metals 2020, 10(7), 934; https://doi.org/10.3390/met10070934 (registering DOI) - 11 Jul 2020
Viewed by 164
Abstract
Transient liquid phase (TLP) bonding is a novel bonding process for the joining of metallic and ceramic materials using an interlayer. TLP bonding is particularly crucial for the joining of the semiconductor chips with expensive die-attached materials during low-temperature sintering. Moreover, the transient [...] Read more.
Transient liquid phase (TLP) bonding is a novel bonding process for the joining of metallic and ceramic materials using an interlayer. TLP bonding is particularly crucial for the joining of the semiconductor chips with expensive die-attached materials during low-temperature sintering. Moreover, the transient TLP bonding occurs at a lower temperature, is cost-effective, and causes less joint porosity. Wire bonding is also a common process to interconnect between the power module package to direct bonded copper (DBC). In this context, we propose to review the challenges and advances in TLP and ultrasonic wire bonding technology using Sn-based solders for power electronics packaging. Full article
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Open AccessArticle
Effect of Backing Plate Materials in Micro-Friction Stir Butt Welding of Dissimilar AA6061-T6 and AA5052-H32 Aluminum Alloys
Metals 2020, 10(7), 933; https://doi.org/10.3390/met10070933 (registering DOI) - 10 Jul 2020
Viewed by 188
Abstract
Thin sheets of lightweight aluminum alloys, which are increasingly used in automotive, aerospace, and electronics industries to reduce the weight of parts, are difficult to weld. When applying micro-friction stir welding (μ-FSW) to thin plates, the heat input to the base materials is [...] Read more.
Thin sheets of lightweight aluminum alloys, which are increasingly used in automotive, aerospace, and electronics industries to reduce the weight of parts, are difficult to weld. When applying micro-friction stir welding (μ-FSW) to thin plates, the heat input to the base materials is considerably important to counter the heat loss to the jig and/or backing plate. In this study, three different backing-plate materials—cordierite ceramic, titanium alloy, and copper alloy—were used to evaluate the effect of heat loss on weldability in the μ-FSW process. One millimeter thick AA6061-T6 and AA5052-H32 dissimilar aluminum alloy plates were micro-friction stir welded by a butt joint. The tensile test, hardness, and microstructure of the welded joints using a tool rotational speed of 9000 rpm, a welding speed of 300 mm/min, and a tool tilting angle of 0° were evaluated. The heat loss was highly dependent on the thermal conductivity of the backing plate material, resulting in variations in the tensile strength and hardness distribution of the joints prepared using different backing plates. Consequently, the cordierite backing plate exhibited the highest tensile strength of 222.63 MPa and an elongation of 10.37%, corresponding to 86.7% and 58.4%, respectively, of those of the AA5052-H32 base metal. Full article
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Open AccessArticle
Empirical Models for Surface Roughness and Topography in 5-Axis Milling Based on Analysis of Lead Angle and Curvature Radius of Sculptured Surfaces
Metals 2020, 10(7), 932; https://doi.org/10.3390/met10070932 (registering DOI) - 10 Jul 2020
Viewed by 162
Abstract
The orientation of the tool axis and the variable curvature of the machined profile of a sculptured surface have a significant impact on the roughness and topography of the surface in the process of 5-axis milling by means of a toroidal milling cutter. [...] Read more.
The orientation of the tool axis and the variable curvature of the machined profile of a sculptured surface have a significant impact on the roughness and topography of the surface in the process of 5-axis milling by means of a toroidal milling cutter. The selection of the orientation of the toroidal milling cutter axis relative to the radius of curvature of the machined surface profile is very important as it can provide a better surface quality and an even distribution of roughness parameters. In this paper, an attempt to carry out model tests to obtain mathematical relationships was made. These relationships were to determine the impact of the tool axis orientation and the variable curvature radius of the machined profile on the surface roughness and its topography in the 5-axis milling process of sculptured surfaces. The tests were conducted on an example of a turbine blade made of Inconel 718 alloy. A measurable effect of the work undertaken was the development of model relationships that can be applied in specialized modules of CAM (Computer Aided Manufacturing) systems supporting the programming of 5-axis machining of sculptured surfaces. The models developed will also make it possible to obtain an evenly distributed roughness on the machined sculptured surface, especially on the surface of the turbine blades of the Inconel 718 alloy, as indicated by the results of the tests carried out. Full article
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Open AccessArticle
Adjustment of Isothermal Transformation Diagrams Using Finite-Element Optimization of the Jominy Test
Metals 2020, 10(7), 931; https://doi.org/10.3390/met10070931 - 10 Jul 2020
Viewed by 165
Abstract
A practical method for adjusting and optimizing isothermal transformation (IT) diagrams using the Jominy test is presented. The method is based on a finite-element optimization procedure, which iteratively minimizes the error between the target phase fractions and the corresponding finite-element solutions at the [...] Read more.
A practical method for adjusting and optimizing isothermal transformation (IT) diagrams using the Jominy test is presented. The method is based on a finite-element optimization procedure, which iteratively minimizes the error between the target phase fractions and the corresponding finite-element solutions at the sample points using an optimization tool. A standard Jominy test of AISI 52100 bearing steel is used to investigate the feasibility and reliability of the method. Three optimization parameters for each IT diagram curve are mathematically applied to the modified Kirkaldy model. These parameters are the design variables in the optimization. The curves obtained from the modified Kirkaldy model are used as the initial guesses in the optimization and they approach the experimental IT diagram by minimizing the error. Good agreement is observed between the optimized diagram and the experimental diagram reported in the literature. The predicted phase fractions using the experimental IT diagram, the IT diagram obtained from the modified Kirkaldy model, and those obtained from the optimized model are compared and demonstrate that the adjustment or optimization procedure significantly improves the accuracy of the predicted phase fraction of the model. The applicability of the method is investigated in a practical case study. Full article
Open AccessArticle
Feeling Machine for Process Monitoring of Turning Hybrid Solid Components
Metals 2020, 10(7), 930; https://doi.org/10.3390/met10070930 - 10 Jul 2020
Viewed by 169
Abstract
The realization of the increasing automation of production systems requires the guarantee of process security as well as the resulting workpiece quality. For this purpose, monitoring systems are used, which monitor the machining based on machine control signals and external sensors. These systems [...] Read more.
The realization of the increasing automation of production systems requires the guarantee of process security as well as the resulting workpiece quality. For this purpose, monitoring systems are used, which monitor the machining based on machine control signals and external sensors. These systems are challenged by innovative design concepts such as hybrid components made of different materials, which lead to new disturbance variables in the process. Therefore, it is important to obtain as much process information as possible in order to achieve a robust and sensitive evaluation of the machining. Feeling machines with force sensing capabilities represent a promising approach to assist the monitoring. This paper provides, for the first time, an overview of the suitability of the feeling machine for process monitoring during turning operations. The process faults tool breakage, tool wear, and the variation of the material transition position of hybrid shafts that were researched and compared with a force dynamometer. For the investigation, longitudinal turning processes with shafts made of EN AW-6082 and 20MnCr5 were carried out. The results show the feeling machine is sensitive to all kinds of examined errors and can compete with a force dynamometer, especially for roughing operations. Full article
(This article belongs to the Special Issue Hybrid Bulk Metal Components)
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Open AccessArticle
Mössbauer and X-ray Studies of Phase Composition of Fly Ashes Formed after Combustion of Ekibastuz Coal (Kazakhstan)
Metals 2020, 10(7), 929; https://doi.org/10.3390/met10070929 - 10 Jul 2020
Viewed by 175
Abstract
Mössbauer spectroscopy and X-ray diffraction have been used to study samples of fly ashes formed after combustion of coal from the Ekibastuz basin at the thermal power plants TPP-2 and TPP-3 in Almaty (Kazakhstan). It has been established that the fractions of fly [...] Read more.
Mössbauer spectroscopy and X-ray diffraction have been used to study samples of fly ashes formed after combustion of coal from the Ekibastuz basin at the thermal power plants TPP-2 and TPP-3 in Almaty (Kazakhstan). It has been established that the fractions of fly ashes contain iron in the form of magnetite Fe3O4 and hematite α-Fe2O3. The mixed valence of iron Fe3+ ↔ Fe2+ in the octahedral sublattice of magnetite is destroyed by isostructural substitution impurities. Maghemite γ-Fe2O3 is additionally present in the fly ash of TPP-3 as a product of magnetite slow oxidation. It was shown that at T ≥ 1400 °C the proportion of magnetite in fly ashes increases due to decomposition of hematite, maghemite, hercynite and the drop of iron content in mullite. It was concluded that the amount of iron in magnetite is a temperature indicator of fly ashes formation. The parameters of hyperfine interactions have been determined in the iron-containing minerals of fly ashes. It was identified that formation of the fly ashes structure occurs in oxidizing atmosphere, since no traces were revealed of reducing environment effect on the phase composition. Full article
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Open AccessArticle
Marked Degradation of Tensile Properties Induced by Plastic Deformation after Interactions between Strain-Induced Martensite Transformation and Hydrogen for Type 316L Stainless Steel
Metals 2020, 10(7), 928; https://doi.org/10.3390/met10070928 - 10 Jul 2020
Viewed by 159
Abstract
Marked degradation of tensile properties induced by plastic deformation after dynamic interactions between strain-induced martensite transformation and hydrogen has been investigated for type 316L stainless steel by hydrogen thermal desorption analysis. Upon modified hydrogen charging reported previously, the amount of hydrogen desorbed in [...] Read more.
Marked degradation of tensile properties induced by plastic deformation after dynamic interactions between strain-induced martensite transformation and hydrogen has been investigated for type 316L stainless steel by hydrogen thermal desorption analysis. Upon modified hydrogen charging reported previously, the amount of hydrogen desorbed in the low temperature range increases; the degradation of tensile properties induced by interactions between plastic deformation and hydrogen at 25 °C or induced by interactions between martensite transformation and hydrogen at −196 °C occurs even for the stainless steel with high resistance to hydrogen embrittlement. The hydrogen thermal desorption behavior is changed by each interaction, suggesting changes in hydrogen states. For specimen fractured at 25 °C, the facet-like morphology and transgranular fracture are observed on the outer part of the fracture surface. At −196 °C, a quasi-cleave fracture is observed at the initiation area. Modified hydrogen charging significantly interacts both plastic deformation and martensite transformation, eventually enhancing the degradation of tensile properties. Upon plastic deformation at 25° C after the interactions between martensite transformation and hydrogen by straining to 0.2 at −196 °C, cracks nucleate in association with martensite formed by the interactions at −196 °C and marked degradation of tensile properties occurs. It is likely that the interactions between martensite transformation and hydrogen induce damage directly related to the degradation, thereby affecting subsequent deformation. Upon dehydrogenation after the interactions between the martensite transformation and hydrogen, no degradation of tensile properties is observed. The damage induced by the interactions between martensite transformation and hydrogen probably changes to harmless defects during dehydrogenation. Full article
Open AccessArticle
Microstructure and Mechanical Properties of Multicomponent Metal Ti(C,N)-Based Cermets
Metals 2020, 10(7), 927; https://doi.org/10.3390/met10070927 - 10 Jul 2020
Viewed by 170
Abstract
Ti(C,N)-based cermets with multicomponent ingredients were prepared using vacuum sintering technology. The effect of molding agents, binder phase and sintering temperature on Ti(C,N)-based cermets were studied. The optimum molding performance was obtained by adding 2% polyvinyl alcohol (PVA-1788). The microstructure and mechanical properties [...] Read more.
Ti(C,N)-based cermets with multicomponent ingredients were prepared using vacuum sintering technology. The effect of molding agents, binder phase and sintering temperature on Ti(C,N)-based cermets were studied. The optimum molding performance was obtained by adding 2% polyvinyl alcohol (PVA-1788). The microstructure and mechanical properties of Ti(C,N)-based cermets were investigated. The Ti(C,N)-based cermet with a weight percentage of TiC:TiN:Ni:Co:Mo:WC:Cr3C2:C = 40:10:20:10:7:8:4:1 and sintered at 1450 °C had the optimal mechanical properties. The relative bending strength, Vickers hardness, elastic modulus and wear resistance were 2010 MPa, 15.01 GPa, 483.57 GPa and 27 mg, respectively. Additionally, X-ray diffraction (XRD), backscatter scanning electron microscopy pictures (SEM–BSE), energy dispersive spectrometry (EDS) and optical micrographs of Ti(C,N)-based cermets were characterized. Full article
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Open AccessArticle
Influence of the Feed Powder Composition in Mechanical Properties of AlN-Nano-Reinforced Aluminium Composites Coatings Deposited by Reactive Direct Laser Deposition
Metals 2020, 10(7), 926; https://doi.org/10.3390/met10070926 - 10 Jul 2020
Viewed by 173
Abstract
Aluminium matrix composite coatings reinforced with AlN nanopaticles have been manufactured by direct laser deposition on an AA6082 alloy substrate. The reinforcement of the composite has been generated by the direct nitridation reaction of the feed powder with the carrier gas (N2 [...] Read more.
Aluminium matrix composite coatings reinforced with AlN nanopaticles have been manufactured by direct laser deposition on an AA6082 alloy substrate. The reinforcement of the composite has been generated by the direct nitridation reaction of the feed powder with the carrier gas (N2) heated by an HPDL beam during the fabrication of the coating. The coating obtained consists of nano-sized AlN particles in an aluminium matrix, and the crystalline structure of the obtained AlN depends on the characteristics of the powder used. In this work, the influence of the feed powder composition is studied by comparison among pure aluminium, Al12-Si alloy, and AA6061 alloy, on the formation of AlN and its crystalline structure. A correlation was established between the temperature distribution reached by the particles, their composition, and the nitridation reaction mechanisms. The effect of the reinforcement was evaluated by comparing the microstructure and mechanical properties (microhardness, nanoindentation) of the composite costing with non-reinforced Al coatings and uncoated AA6082. Al/AlN composite coatings with improved properties were achieved, reaching hardness values that were 65% higher than coatings without reinforcement. Full article
(This article belongs to the Special Issue Aluminum Alloys and Aluminum Matrix Composites)
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Open AccessArticle
Application of the Cumulative Kinetic Model in the Comminution of Critical Metal Ores
Metals 2020, 10(7), 925; https://doi.org/10.3390/met10070925 - 09 Jul 2020
Viewed by 237
Abstract
Over the last decades, several reliable mathematical models have been developed for simulating ore comminution processes and determining the Work Index. Since Fred Chester Bond developed the Work Index standard procedure in 1961, numerous attempts have been made to find simpler, faster, and [...] Read more.
Over the last decades, several reliable mathematical models have been developed for simulating ore comminution processes and determining the Work Index. Since Fred Chester Bond developed the Work Index standard procedure in 1961, numerous attempts have been made to find simpler, faster, and economically more advantageous alternative tests. In this paper, a Bond test simulation based on the cumulative kinetic model (CKM) has been checked on a spreadsheet. The research has been accomplished by conventionally determining the kinetic parameters for some Ag and Au ores and for three pure minerals and one rock that are common constituents of the gangue rock. Analysis of the results obtained allowed to develop a simplified procedure for calculating the kinetic parameters and their application to Work Index determination through simulation. Full article
(This article belongs to the Special Issue Grinding and Concentration Technology of Critical Metals)
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Open AccessArticle
Tribological Properties of Ti2AlNb Matrix Composites Containing Few-Layer Graphene Fabricated by Spark Plasma Sintering
Metals 2020, 10(7), 924; https://doi.org/10.3390/met10070924 - 09 Jul 2020
Viewed by 244
Abstract
Ti2AlNb alloys with few-layer graphene were fabricated by spark plasma sintering (SPS) to enhance the tribological properties (TP) of the composite materials. Microstructure characteristics of the original few-layer graphene (FLG), Ti2AlNb powders, and the sintered composites were characterized by [...] Read more.
Ti2AlNb alloys with few-layer graphene were fabricated by spark plasma sintering (SPS) to enhance the tribological properties (TP) of the composite materials. Microstructure characteristics of the original few-layer graphene (FLG), Ti2AlNb powders, and the sintered composites were characterized by X-Ray Diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The experimental results indicated that FLGs were homogeneously distributed in the composites. Tribological results indicated that the coefficient of friction (COF) of the composites was reduced as the content of FLG increased. Compared with the pure Ti2AlNb alloy, the average COF of the composite with 1.0 wt.% FLG was decreased by 9.4% and the wear rate was decreased by 36%. Meanwhile, the microstructures of the worn surface showed that TiC particles and friction layers formed by residual FLGs were present on the surface of the composites after tribological test. It is proposed that Ti2AlNb alloys with FLGs presented the enhanced wear resistance. Full article
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Open AccessArticle
A Modular Machine-Learning-Based Approach to Improve Tensile Properties Uniformity Along Hot Dip Galvanized Steel Strips for Automotive Applications
Metals 2020, 10(7), 923; https://doi.org/10.3390/met10070923 - 09 Jul 2020
Viewed by 236
Abstract
The paper presents a machine learning-based system aimed at improving the homogeneity of tensile properties of steel strips for automotive applications over their strip length in the annealing and hot dip galvanizing lines. A novel modular approach is proposed exploiting process and product [...] Read more.
The paper presents a machine learning-based system aimed at improving the homogeneity of tensile properties of steel strips for automotive applications over their strip length in the annealing and hot dip galvanizing lines. A novel modular approach is proposed exploiting process and product data and combining smart data pre-processing and cleansing algorithms, an ensemble of neural networks targeted to specific product classes and an ad-hoc developed iterative procedure for identifying the variability ranges of the most relevant process variables. A decision support concept is implemented through a software tool, which facilitates exploitation by plant managers and operators. The system has been tested on site. The results show its effectiveness in improving the control of the thermal evolution of the strip with respect to the standard operating practice. Full article
(This article belongs to the Special Issue Applied Artificial Intelligence in Steelmaking)
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Open AccessFeature PaperArticle
Hydrogen Ironmaking: How It Works
Metals 2020, 10(7), 922; https://doi.org/10.3390/met10070922 (registering DOI) - 09 Jul 2020
Viewed by 193
Abstract
A new route for making steel from iron ore based on the use of hydrogen to reduce iron oxides is presented, detailed and analyzed. The main advantage of this steelmaking route is the dramatic reduction (90% off) in CO2 emissions compared to [...] Read more.
A new route for making steel from iron ore based on the use of hydrogen to reduce iron oxides is presented, detailed and analyzed. The main advantage of this steelmaking route is the dramatic reduction (90% off) in CO2 emissions compared to those of the current standard blast-furnace route. The first process of the route is the production of hydrogen by water electrolysis using CO2-lean electricity. The challenge is to achieve massive production of H2 in acceptable economic conditions. The second process is the direct reduction of iron ore in a shaft furnace operated with hydrogen only. The third process is the melting of the carbon-free direct reduced iron in an electric arc furnace to produce steel. From mathematical modeling of the direct reduction furnace, we show that complete metallization can be achieved in a reactor smaller than the current shaft furnaces that use syngas made from natural gas. The reduction processes at the scale of the ore pellets are described and modeled using a specific structural kinetic pellet model. Finally, the differences between the reduction by hydrogen and by carbon monoxide are discussed, from the grain scale to the reactor scale. Regarding the kinetics, reduction with hydrogen is definitely faster. Several research and development and innovation projects have very recently been launched that should confirm the viability and performance of this breakthrough and environmentally friendly ironmaking process. Full article
(This article belongs to the Special Issue Challenges and Prospects of Steelmaking Towards the Year 2050)
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Open AccessArticle
Quasi-Static Compression Deformation and Energy Absorption Characteristics of Basalt Fiber-Containing Closed-Cell Aluminum Foam
Metals 2020, 10(7), 921; https://doi.org/10.3390/met10070921 - 09 Jul 2020
Viewed by 183
Abstract
In this work, closed-cell aluminum foams with 4 wt.% contents of short-cut basalt fibers (BFs) were successful prepared by using the modified melt-foaming method. The pore size of BF-containing aluminum foam and commercially pure aluminum foam was counted. The distribution of BF and [...] Read more.
In this work, closed-cell aluminum foams with 4 wt.% contents of short-cut basalt fibers (BFs) were successful prepared by using the modified melt-foaming method. The pore size of BF-containing aluminum foam and commercially pure aluminum foam was counted. The distribution of BF and its effect on the compressive properties of closed-cell aluminum foams were investigated. The results showed that the pore size of BF-containing aluminum foams was more uniform and smaller. BF mainly existed in three different forms: Some were totally embedded in the cell walls, some protruded from the cell walls, and others penetrated through the cells. Meanwhile, under the present condition, BF-containing aluminum foams possessed higher compressive strength and energy absorption characteristics than commercially pure aluminum foams, and the reasons were discussed. Full article
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Open AccessArticle
Characterization of Hot Deformation Behavior and Dislocation Structure Evolution of an Advanced Nickel-Based Superalloy
Metals 2020, 10(7), 920; https://doi.org/10.3390/met10070920 - 09 Jul 2020
Viewed by 177
Abstract
The hot deformation behavior of an advanced nickel-based Haynes282 superalloy was systematically investigated employing isothermal compression tests in the sub-solvus and super-solvus temperature with various strain rates. The influence of deformation temperature and strain rate on the microstructure was studied by transmission electron [...] Read more.
The hot deformation behavior of an advanced nickel-based Haynes282 superalloy was systematically investigated employing isothermal compression tests in the sub-solvus and super-solvus temperature with various strain rates. The influence of deformation temperature and strain rate on the microstructure was studied by transmission electron microscope. The results reveal that the interaction between work hardening and dynamic softening did not reach equilibrium under lower deformation temperature and higher strain rate. The active energy of alloy is around 537.12 kJ/mol and its hot deformation constitutive relationship equation was expressed. According to the processing map and microstructure observations, two unsafe flow instability domains should be avoided. The optimum hot processing condition for homogeneous and fine dynamic recrystallization grains are obtained. TEM micrograph observations indicated that deformation temperature and strain rate affected recrystallization by affecting the evolution of dislocation substructures within the alloy. The nucleation and growth of DRX grains can be promoted by the relatively high deformation temperature and low strain rate. The main mechanism of dynamic recrystallization nucleation preferred to discontinuous dynamic recrystallization and the typical feature of discontinuous dynamic recrystallization showed grain boundary migration nucleation. The findings improve the understanding of hot deformation behavior and dislocation substructures evolution of the superalloy, which benefits the accurate control of microstructures of nickel-based superalloys, and tailors the properties of final components used in the land-based gas turbine. Full article
(This article belongs to the Special Issue Advances in Superalloys and High Temperature Intermetallics)
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Open AccessArticle
Influence of the Energy Density for Selective Laser Melting on the Microstructure and Mechanical Properties of Stainless Steel
Metals 2020, 10(7), 919; https://doi.org/10.3390/met10070919 - 09 Jul 2020
Viewed by 188
Abstract
We have investigated the impact of the process parameters for the selective laser melting (SLM) of the stainless steel AISI 316L on its microstructure and mechanical properties. Properly selected SLM process parameters produce tailored material properties, by varying the laser’s power, scanning speed [...] Read more.
We have investigated the impact of the process parameters for the selective laser melting (SLM) of the stainless steel AISI 316L on its microstructure and mechanical properties. Properly selected SLM process parameters produce tailored material properties, by varying the laser’s power, scanning speed and beam diameter. We produced and systematically studied a matrix of samples with different porosities, microstructures, textures and mechanical properties. We identified a combination of process parameters that resulted in materials with tensile strengths up to 711 MPa, yield strengths up to 604 MPa and an elongation up to 31%, while the highest achieved hardness was 227 HV10. The correlation between the average single-cell diameter in the hierarchical structure and the laser’s input energy is systematically studied, discussed and explained. The same energy density with different SLM process parameters result in different material properties. The higher energy density of the SLM produces larger cellular structures and crystal grains. A different energy density produces different textures with only one predominant texture component, which was revealed by electron-backscatter diffraction. Furthermore, three possible explanations for the origin of the dislocations are proposed. Full article
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Open AccessArticle
Effects of Rare Earth Elements on Microstructure and Mechanical Properties of H13 Die Steel
Metals 2020, 10(7), 918; https://doi.org/10.3390/met10070918 - 09 Jul 2020
Viewed by 175
Abstract
The effects of rare earth (RE) elements on the carbide distribution, transformation temperature, and mechanical properties of H13 die steels after annealing were systematically investigated by scanning electron microscopy, electron probe microanalysis, and transmission electron microscopy. The results indicated that the addition of [...] Read more.
The effects of rare earth (RE) elements on the carbide distribution, transformation temperature, and mechanical properties of H13 die steels after annealing were systematically investigated by scanning electron microscopy, electron probe microanalysis, and transmission electron microscopy. The results indicated that the addition of RE elements is helpful in increasing the fraction of the disrupted M23C6 carbide along the grain boundaries, hindering the migration of grain boundaries and improving the crack-formation and expansion resistance of the carbides in the tensile process. With the addition of RE, the Ac3 temperature increased by 11.4 °C and the diffusion of carbon atoms was pinned during the austenitizing process. Moreover, the carbides were modified by rare earth elements, and RE-inclusion promoted the transition of brittle-type failure to ductile-type failure. Therefore, the impact energy, hardness, and ultimate tensile strength improved significantly in the RE-modified H13 die steels. Full article
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Open AccessArticle
Effect of Ultrasonic Surface Rolling Treatment on Corrosion Behavior of Alloy 690
Metals 2020, 10(7), 917; https://doi.org/10.3390/met10070917 - 09 Jul 2020
Viewed by 179
Abstract
The nanograins (NG) on the top surface layer of alloy 690 were successfully prepared by ultrasonic surface rolling treatment (USRT). The average grain size of NG alloy 690 was 55 nm, and the thickness of the NG surface layer was about 1 μm. [...] Read more.
The nanograins (NG) on the top surface layer of alloy 690 were successfully prepared by ultrasonic surface rolling treatment (USRT). The average grain size of NG alloy 690 was 55 nm, and the thickness of the NG surface layer was about 1 μm. Meanwhile, the surface roughness was significantly reduced after surface nanocrystalliztion. The corrosion behavior of alloy 690 before and after USRT was studied in a secondary side environment containing chloride. Electrochemical corrosion experiments demonstrated that the passive film generated by USRT was denser than that formed on coarse-grained (CG) alloy 690. Pitting corrosion was prone to occur in grain boundaries of CG alloy 690, and the pits on the surface of NG alloy 690 were smaller than those generated on CG alloy 690 after 1000 h of an immersion experiment. Full article
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Open AccessArticle
Calcium Doped Flash-PEO Coatings for Corrosion Protection of Mg Alloy
Metals 2020, 10(7), 916; https://doi.org/10.3390/met10070916 - 09 Jul 2020
Viewed by 259
Abstract
This study demonstrates a significant improvement of the corrosion resistance of an AZ31B magnesium alloy achieved by the application of 1 μm-thin coatings generated by an environmentally friendly flash plasma electrolytic oxidation (FPEO) process in Ca-containing electrolytes. Two compounds with different solubility, calcium [...] Read more.
This study demonstrates a significant improvement of the corrosion resistance of an AZ31B magnesium alloy achieved by the application of 1 μm-thin coatings generated by an environmentally friendly flash plasma electrolytic oxidation (FPEO) process in Ca-containing electrolytes. Two compounds with different solubility, calcium oxide (CaO) or calcium glycerophosphate (CaGlyP), were used as sources of Ca in the electrolyte. Very short durations (20–45 s) of the FPEO process were employed with the aim of limiting the energy consumption. The corrosion performance of the developed coatings was compared with that of a commercial conversion coating (CC) of similar thickness. The viability of the coatings in a full system protection approach, consisting of FPEO combined with an inhibitor-free epoxy primer, was verified in neutral salt spray and paint adhesion tests. The superior corrosion performance of the FPEO_CaGlyP coating, both as a stand-alone coating and as a full system, was attributed to the formation of a greater complexity of Ca2+ bonds with SiO2 and PO43− species within the MgO ceramic network during the in situ incorporation of Ca into the coating from a double chelated electrolyte and the resultant difficulties with the hydrolysis of such a network. The deterioration of the FPEO_CaGlyP coating during immersion was found over ten times slower compared with Ca-free flash-PEO coating. Full article
(This article belongs to the Special Issue Corrosion and Inhibition Processes)
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Open AccessArticle
Enhancing Surface Topology of Udimet®720 Superalloy through Ultrasonic Vibration-Assisted Ball Burnishing
Metals 2020, 10(7), 915; https://doi.org/10.3390/met10070915 - 08 Jul 2020
Viewed by 232
Abstract
This contribution reports the effects of an ultrasonic-vibration assisted ball burnishing process on the topological descriptors of nickel-based alloy Udimet®720. This material is of high interest for the transportation industry, and specifically for the aeronautical sector. Despite the acknowledged necessity to finish this [...] Read more.
This contribution reports the effects of an ultrasonic-vibration assisted ball burnishing process on the topological descriptors of nickel-based alloy Udimet®720. This material is of high interest for the transportation industry, and specifically for the aeronautical sector. Despite the acknowledged necessity to finish this material to achieve excelling mechanical performances of parts, surface integrity enhancement by means of plastic deformation through ball burnishing has seldom been explored in previous references so far. In this paper, different surface descriptors are used to report how the topology changes after ultrasonic-assisted ball burnishing, and how burnishing conditions influence that change. The burnishing preload and the number of passes are the only influential factors on surface change, whereas the feed velocity of the tool and the strategy reveal not to be relevant on the result. Additionally, the extent to which the process successfully modifies the objective surfaces is highly divergent depending on the original scale of the treated surface. The assistance of the process with vibrations also shows that the resulting topologies are characterized by a periodical pattern of repetitive peaks and valleys that are extended on the surface with a higher frequency in comparison to the non-assisted process, which could influence in the functional deployment of workpieces treated through it, and could deliver an advantage with regard to its non-assisted homologous process. Full article
(This article belongs to the Special Issue Advances in Plastic Deformation Technologies)
Open AccessArticle
Torque-Based Temperature Control in Friction Stir Welding by Using a Digital Twin
Metals 2020, 10(7), 914; https://doi.org/10.3390/met10070914 - 08 Jul 2020
Viewed by 251
Abstract
Friction stir welding (FSW) is an innovative solid-state welding technology that produces high quality joints and is widely used in the aerospace industry. Previous studies have revealed welding temperature to be a decisive factor for joint quality. Consequently, several temperature control systems for [...] Read more.
Friction stir welding (FSW) is an innovative solid-state welding technology that produces high quality joints and is widely used in the aerospace industry. Previous studies have revealed welding temperature to be a decisive factor for joint quality. Consequently, several temperature control systems for FSW have been developed. These output feedback control systems usually require delicate and expensive temperature measuring equipment, which reduces their suitability for industrial practice. This paper presents a novel state feedback system of the welding temperature to remedy this shortcoming. The system uses a physical model of the FSW process (digital twin) for the determination of the welding temperature signal from the process torque signal. The digital twin is based on a multi-input nonlinear time invariant model, which is fed with the torque signal from the spindle motor. A model-based L1 adaptive controller was employed for its robustness with respect to model inaccuracies and fast adaption to fluctuations in the controlled system. The experimental validation of the feedback control system showed improved weld quality compared to welded joints produced without temperature control. The achieved control accuracies depended on the results of the temperature calculation. Control deviations of less than 10 K could be achieved for certain welding parameters, and even for a work piece geometry, which deliberately caused heat accumulation. Full article
Open AccessArticle
Study on the Relationship between Root Metal Flow Behavior and Root Flaw Formation of a 2024 Aluminum Alloy Joint in Friction Stir Welding by a Multiphysics Field Model
Metals 2020, 10(7), 913; https://doi.org/10.3390/met10070913 - 08 Jul 2020
Viewed by 207
Abstract
In friction stir welding (FSW), many defects (such as kissing bond, incomplete penetration, and weak connection) easily occur at the root of the welded joint. Based on the Levy–Mises yield criterion of the Zener–Hollomon thermoplastic constitutive equation, a 3D thermal–mechanical coupled finite element [...] Read more.
In friction stir welding (FSW), many defects (such as kissing bond, incomplete penetration, and weak connection) easily occur at the root of the welded joint. Based on the Levy–Mises yield criterion of the Zener–Hollomon thermoplastic constitutive equation, a 3D thermal–mechanical coupled finite element model was established. The material flow behavior and the stress field at the root area of a 6 mm thick 2024-T3 aluminum alloy FSW joint were studied. The influence of pin length on the root flaw was investigated, and the formation mechanism of the “S line” defects and non-penetration defects were revealed. The research results showed that the “S line” defect forms near the bottom surface of the pin owing to the insufficiently mixed material from the advancing side (AS) and retreating side (RS) near the weld center. The non-penetration defect forms near the bottom surface of the workpiece owing to the insufficient driving force to make the material flow through the weld center. With the continual increase of pin length, the size of the “S line” defect and non-penetration defect reduces, and finally, the defect-free welded joint can be obtained with an optimized suitable length of the pin in this case. Full article
(This article belongs to the Special Issue Advanced Welding Technology in Metals)
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Open AccessArticle
Agglomeration–Flotation of Finely Ground Chalcopyrite Using Emulsified Oil Stabilized by Emulsifiers: Implications for Porphyry Copper Ore Flotation
Metals 2020, 10(7), 912; https://doi.org/10.3390/met10070912 - 08 Jul 2020
Viewed by 217
Abstract
Flotation is the conventional method for processing porphyry copper deposits, one of the most economically important sources of copper (Cu) worldwide. The rapidly decreasing grade of this type of Cu ore in recent years, however, presents serious problems with fine particle recovery using [...] Read more.
Flotation is the conventional method for processing porphyry copper deposits, one of the most economically important sources of copper (Cu) worldwide. The rapidly decreasing grade of this type of Cu ore in recent years, however, presents serious problems with fine particle recovery using conventional flotation circuits. This low recovery could be attributed to the low collision efficiency of fine particles and air bubbles during flotation. To improve collision efficiency and flotation recovery, agglomeration of finely ground chalcopyrite (CuFeS2) (D50 = 3.5 μm) using emulsified oil stabilized by emulsifiers was elucidated in this study. Specifically, the effects of various types of anionic (sodium dodecyl sulfate (SDS), potassium amyl xanthate (KAX)), cationic (dodecyl amine acetate (DAA)), and non-ionic (polysorbate 20 (Tween 20)) emulsifiers on emulsified oil stability and agglomeration–flotation efficiency were investigated. When emulsifiers were added, the average size of agglomerates increased, resulting in higher Cu recovery during flotation. This dramatic improvement in flotation efficiency could be attributed to the smaller oil droplet size in emulsified oil and their higher stability in the presence of emulsifiers. The utilization of emulsifiers during agglomeration–flotation not only lowered the required agitation strength for agglomeration but also shortened the agglomeration time, both of which made the process easier to incorporate in existing flotation circuits. Full article
(This article belongs to the Special Issue Advances in Selective Flotation and Leaching Process in Metallurgy)
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