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In this study, the effect of post heat treatment on microstructural evolution and tensile properties of 0.75% of carbon doped NiCoCr MEA alloy manufactured by laser powder bed fusion (LPBF) was investigated. The post heat treatment of LPBF-built 0.75C MEA alloy was selected and carried out at 700 °C for 1hr, respectively. The microstructural observation in heat-treated 0.75C MEA HT sample shows a lower stacking fault energy (SFE) with wider stacking fault width (SFW) compared to as-built condition. In-situ nano-sized precipitates are formed along the sub-boundaries of the as₋built 0.75C MEA and 0.75C MEA HT samples which are estimated as 1.25 % and 2.45 %, respectively. After post heat treatment process, the size and ratio of nano-sized precipitates enhanced and identified as Cr-rich M23C6 carbide. Subsequently, the yield and tensile strengths increase from 823.2 MPa to 872.7 MPa and 1.05 GPa–1.15 GPa for 0.75C MEA and 0.75C MEA HT conditions, respectively which is attributed to the prevailing solid solution strengthening and precipitation strengthening. The deformation twins in as−built specimen are transformed to twin bundle once the local strain increases from 5% to 20%. The 0.75C MEA HT deformed specimen exhibits high dislocation accumulation with retained stable substructure in local strain 20% area due to the pinning effect of nano-sized precipitates which stabilizes and strengthens the substructure boundary i.e., Dynamic Hall-Petch mechanism. These results provide a new perception for achieving better strength performance by post heat treatment process for NiCoCr-based medium entropy alloys (MEA) alloy.

CrMnFeCoNi high entropy alloy (HEA) which had nano oxide particles formed during additive manufacturing process was fabricated using a selective laser melting (SLM) process (hereinafter SLM Cantor HEA). The microstructure of the fabricated SLM Cantor HEA and the wear properties according to the applied load (5 N, 15 N) were investigated. SLM Cantor HEA was consist of nano-size oxides and high dislocation density, resulting in superior hardness compared to conventional processed CrMnFeCoNi HEA. As a result of the wear test, it showed abrasive and oxidative wear behavior regardless of applied load. But in case of 15 N load condition, it showed more finer worn microstructure with increased wear load, and had a contradictory effect on each friction coefficient and wear rate. Based on the above results, the wear mechanism of in-situ oxide reinforced SLM Cantor HEA was discussed in relation with the microstructure.

A pure molybdenum (Mo) coating layer was manufactured by using the atmospheric plasma spray (APS) process and its wear and corrosion characteristics were investigated in this study. A Mo coating layer was prepared to a thickness of approximately 480 μm, and it had sound physical properties with a porosity of 2.9% and hardness of 434 Hv. Room temperature dry wear characteristics were measured through a ball-on-disk test under load conditions of 5 N, 10 N and 15 N. Based on the coefficient of friction graph at 5 N and 10 N, the oxides formed during wear functioned as a wear lubricant, thereby confirming an increase in wear resistance. However, at 15 N, wear behavior changed, and wear occurred due to splat pulling out. A potentiodynamic polarization test was conducted under an artificial seawater atmosphere, and Ecorr and Icorr measured 0.717 V and 7.2E-5 A/cm2, respectively. Corrosion mainly occurred at the splat boundary and pores that were present in the initial state. Based on the findings above, the potential application of APS Mo coating material was also discussed.

The current study intended to manufacture 17-4PH stainless steel using material extrusion additive manufacturing (MEAM) process and to control the microstructure and mechanical properties of the steel through heat treatment. The as sintered MEAM 17-4PH steel was densely manufactured with a 97% or more sintered density and few inter-layer defects. Microstructure images of the prepared specimen showed an isotropic microstructure, and the matrix was mainly composed of lath martensite. After heat treatment (a standard H900 condition), no phase change was observed in the matrix of the specimen, and the dislocation density slightly increased. In the case of nano-sized particles, 16.38 nm 3R structure Cu-rich precipitates (CRP) and some NbC were present in the as sintered steel. A high fraction of BCC structure CRP of size 3.51 nm and NbC of size about 88 nm precipitated in the post-heat-treated specimen. Tensile test of the specimen before the heat treatment (as sintered) showed the best mechanical properties among the MEAM 17-4PH steels reported so far. After the heat treatment, tensile strength, yield strength, and elongation even increased to 1.35 GPa, 1.11 GPa, and 7.8%, respectively. This study also aimed to suggest a method for controlling the properties of the MEAM-built 17-4PH stainless steel to improve its mechanical properties based on its microstructures change and the difference in strengthening mechanisms.

This study investigated the effect of heat treatment on the microstructure and impact toughness property of AISI D2 manufactured with direct energy deposition (DED) and compared the results with conventional wrought material. The fracture crack propagation behavior was examined in connection with microstructures through fracture surface analysis. AISI D2 manufactured with DED had a eutectic structure that turned into a net-type carbide after heat treatment, and Cr-rich needle-type secondary carbide was observed. Impact toughness of DED AISI D2 measured 2.0 J/cm2 in the as-built sample and 1.1 J/cm2 in the heat-treated sample. Compared to a wrought heat-treated AISI D2, DED AISI D2 had relatively low impact toughness. DED AISI D2 and wrought material had different crack propagation mechanisms. In DED AISI D2, the eutectic structure and net-type carbide boundary were identified as the major microstructural factor decreasing impact toughness.

CM247LC alloy was manufactured by using selective laser melting (SLM) process, one of the laser powder bed fusion ­(L-PBF) methods. The hot isostatic pressing (HIP) process was additionally conducted on the SLM-built CM247LC to control its microstructures and defects. The high temperature oxidation property was investigated, and it was compared with conventional DS247LC sample (reference) prepared via the directional solidification process. The L-PBF HIP sample showed blocky-type MC carbides generated along the grain boundary with average size of about 200 nm. A semi-spherical primary γ' phase of size 0.4-1.0 μm was also observed inside the grains. Moreover, the DS247LC sample displayed a coarse eutectic γ' phase and many script-type MC carbides. Furthermore, cuboidal-type γ' with an average size of about 0.5 μm was detected. High-temperature oxidation tests were conducted at 1000°C and 1100°C for 24 hours. The results at 1100°C oxidation temperature showed that the measured oxidation weight gains for HIP and DS247LC were 1.96 mg/cm2 and 2.26 mg/cm2, respectively, indicating the superior high-temperature oxidation resistance of the L-PBF HIP sample. Based on the above results, a high-temperature oxidation mechanism of the CM247LC alloys manufactured by the SLM process and the directional solidification process has been proposed.

Solid-state cold spray additive manufacturing (CSAM) was used to fabricate pure tantalum (Ta) and the high-temperature mechanical and deformation behavior of this material was investigated. The pure Ta fabricated using CSAM consists of irregularly shaped powder particles elongated in the direction perpendicular to the spraying direction. In addition, microstructural evolution occurs in the process of accommodating harsher plastic deformation along the boundaries between powder particles. Compression test results confirmed that the room temperature yield strength was approximately 901 MPa, which is four to six times higher than that of pure Ta produced using conventional processes such as vacuum arc melting etc. Moreover, CSAM Ta has excellent mechanical properties even at high temperatures, and these properties were confirmed to be retained up to approximately 950 °C. Surface and microstructural observations after deformation revealed that the sample crumbled in a compression test at 800 °C. However, the sample retained its shape at temperatures above 800 °C. This phenomenon was a result of the interaction between high-temperature oxidation behavior and microstructural evolution, i.e. dynamic recrystallization. Based on these findings, the relationship among the microstructure, room-to high-temperature mechanical properties, and deformation behaviors are also discussed.

Fe-Cr-B-based metamorphic alloy coating layers were manufactured by plasma spray with a Fe-Cr-B-Mo-Nb composition (hereinafter, M+) powder. The microstructure and wear properties of the coating layers were investigated and compared with a metamorphic alloy coating layer fabricated with commercial M material. XRD analysis revealed that the M and M+ coating layers were composed of α-Fe, (Cr, Fe)2B, and some metallic glass phases. Wear test results showed that M+ coating layers had a superior wear resistance which had 1.48 times lower wear volume than M coating layers. Observations of the worn-out surfaces and cross-sections of the coating layers showed that M+ coating layer had relatively low oxides along the particle boundaries and it suppress a delamination behavior by the oxides.

Co-Cr-Mo based sheet I-WP lattice was fabricated via laser powder bed fusion. The effect of microstructure and the I-WP shape on compressive mechanical response was investigated. Results of compression test showed that yield strength of the sheet I-WP was 176.3 MPa and that of bulk Co-Cr-Mo (reference material) was 810.4 MPa. By applying Gibson-Ashby analytical model, the yield strength of the lattice was reversely estimated from that of the bulk specimen. The calculated strength of the lattice obtained was 150.7 MPa. The shape of deformed lattice showed collective failure mode, and its microstructure showed that strain-induced martensitic transformation occurred in the overall lattice. The deformation behavior of additively manufactured sheet I-WP lattice was also discussed.

MoO3 thick film was manufactured by using a thermal spray process (Atmospheric Plasma Spray, or APS) and its microstructure, phase composition and properties of the coating layer were investigated. Initial powder feedstock was composed of an orthorhombic α-MoO3 phase, and the average powder particle size was 6.7 μm. As a result of the APS coating process, a MoO3 coating layer with a thickness of about 90 μm was obtained. Phase transformation occurred during the process, and the coating layer consisted of not only α-MoO3 but also β-MoO3, MoO2. Phase transformation could be due to the rapid cooling that occurred during the process. The properties of the coating layer were evaluated using a nano indentation test. Hardness and reduced modulus were obtained as 0.47 GPa and 1.4 GPa, respectively. Based on the above results, the possibility of manufacturing a MoO3 thick coating layer using thermal spray is presented.

A carbon–containing CrMnFeCoNi high–entropy alloy (C–HEA) nanocomposite was additively manufactured via a laser powder bed fusion (LPBF) process combined with subsequent heat treatment. Exposure of the LPBF C–HEA to this additional heat–treatment step not only resulted in heterogeneous–structured grains of which the substructure is decorated with a dislocation network, but also uniformly distributed nanosized carbide precipitates at the grain and substructure boundaries. A multistep creep test conducted on the LPBF C–HEA at 873 K enabled the stress exponent, n, to be obtained with values of 3.03 in the low stress region (175–250 MPa) and 6.99 in the high stress region (250–325 MPa). The LPBF C–HEA alloy exhibited superior high–temperature creep resistance (i.e., the creep rate and threshold stress were minimized) compared to other CrMnFeCoNi HEAs. The mechanism underlying the creep resistance and unique creep deformation behavior of the LPBF C–HEA alloy is discussed on the basis of electron channeling contrast imaging and electron backscatter diffraction analyses.

CoCrMo sheet triply periodic minimal surface (sheet-TPMS) lattices with two different topologies (Neovius, IWP) were fabricated by laser power bed fusion (LPBF). Compressive behavior and energy absorption characteristic for each topology and direction were investigated. The unique pore channel structures of the fabricated Neovius and IWP lattices were well formed. The microstructural observation revealed that fine cellular substructures existed inside the sheets, and most of their constituent phases were confirmed to be the FCC phase. The results of the compression tests demonstrated that Neovius lattice had higher yield strength and first peak strength than IWP lattice, regardless of the compressive direction. As for the stress–strain curves of the lattices, an abrupt stress drop was found in neither of the two topologies. A comparison of the energy absorption characteristics confirmed that Neovius lattice had higher energy absorption efficiency and ideality than IWP lattice. The deformed structures showed that Neovius lattice displayed a gradual collapse mode, whereas a layer-by-layer compaction mode was indicated in IWP lattice. After the deformation, Neovius showed an evenly distributed and high fraction of the HCP phase caused by strain-induced martensitic transformation. The topology of lattice and strain-induced martensitic transformation effects on the compressive mechanical responses of the LPBF-built TPMS lattices were also discussed.

In this study, high-purity tantalum metal powder was manufactured via self-propagating high-temperature synthesis. During the process, Ta2O5 and Mg were used as the raw material powder and the reducing agent, respectively, and given that combustion rate and reaction temperature are important factors that influence the success of this process, these factors were controlled by adding an excessive mass of the reducing agent (Mg) i.e., above the chemical equivalent, rather than by using a separate diluent. It was confirmed that Ta metal powder manufactured after the process was ultimately manufactured 99.98% high purity Ta metal powder with 0.5 µm particle size. Thus, it was observed that adding the reducing reagent in excess favored the manufacture of high-purity Ta powder that can be applied in capacitors.

The objective of the present work was to investigate the effect of different cermet coatings on tensile and high-cycle fatigue properties of AISI 1045 steel using High-Velocity Oxygen Fuel (HVOF) thermal spray process. In this study, the WC-12Co, WC-10Co-4Cr, and Cr3C2–25NiCr cermet powders were coated onto the surface of annealed AISI 1045 steel specimens via the HVOF thermal spray process. The corresponding HVOF thermal spraying results were compared with those obtained from hard chrome (Cr) electroplating process. The thermal spray coated specimens showed load drop tendency beyond the yield point with significant work hardening in the tensile results, but low fatigue life than the base material in high-cycle fatigue results due to defects and poor adhesion at the interface. However, those cermet coating materials showed higher fatigue strengths than the hard chrome plated material. Fractography tests showed that fatigue strength was not only dependent on residual stress, but also influenced by the modes of fatigue failure related to the coated layer's cohesion and adhesion strength. Overall, the Cr3C2–25NiCr cermet coating is preferable due to its less porosity, high fatigue property, and better adhesion than the other coated materials.

Oxide-dispersion-strengthened high-entropy alloys were produced by hot-pressing a ball-milled mixture of Y2O3 and atomized CoCrFeMnNi powder. The effect of milling duration on grain size reduction, oxide formation behavior, and the resulting mechanical properties of the alloys was studied. Both the alloy powder size and Y2O3 particle size decreased with milling time. Moreover, the alloy powder experienced severe plastic deformation, dramatically generating crystalline defects. As a result, the grain size was reduced to ~16.746 nm and in-situ second phases (e.g., MnO2 and σ phase) were formed at the defects. This increased the hardness of the alloys up to a certain level, although excessive amounts of in-situ second phases had the reverse effect.

In order to the long-term stability of DSE for electroplating process, the lifetime equations were calculated from the results of the accelerated life testing, and the lifetime of DSE was predicted. The nano-embossing pre-treatment led to 2.65 times in the lifetime of DSE. The degradation mechanism of DSE with a thick metal oxide layer for applied highly current density process condition was identified. The improvement of durability of DSE seems to be closely related to adhesion between titanium plate and mixed metal oxide layer.

In this study, the effect of the addition of ZrO2 and Al2O3 ceramic powders to Cu-Mo-Cr alloy was studied by examining the physical properties of the composite material. The ceramic additives were selected based on the thermodynamic stability calculation of the Cu-Mo-Cr alloys. Elemental powders, in the ratio Cu:Mo:Cr = 60:30:10 (wt.%), and approximately 0-1.2 wt.% of ZrO2 and Al2O3 were mixed, and a green compact was formed by pressing the mixture under 186 MPa pressure and sintering at 1250°C for 5 h. The raw powders were evenly dispersed in the mixed powder, as observed by scanning electron microscopy. After sintering, the microstructures, densities, electrical conductivities, and hardness of the composites were evaluated. We found that the addition of ZrO2 and Al2O3 increased the hardness and decreased the electrical conductivity and density of the composites.

This study fabricated a WC/T-800 cermet coating layer with Co-Mo-Cr (T-800) powder and WC powder using laser cladding, and analyzed its microstructure, hardness and wear properties. For comparison, casted bulk T-800 was used. Laser cladded ­WC/T-800 cermet coating layer showed circular WC phases in the Co matrix, and dendritic laves phases. The average laves phase size in the cermet coating layer and bulk T-800 measured as 7.9 µm and 60.6 µm, respectively, indicating that the cermet coating layer had a relatively finer laves phase. Upon conducting a wear test, the cermet coating layer added with WC showed better wear resistance. In the case of laser cladded WC/T-800 cermet coating layer, abrasion wear was observed; on the contrary, the bulk T-800 showed pulled out laves phases. Based on the above findings, the WC/T-800 cermet coating layer using laser cladding and the relationship between its microstructure and wear behavior were discussed.

The effects of severe plastic deformation on the microstructural evolution, tensile and high cycle fatigue properties of warm caliber-rolled hypereutectoid steels were investigated. As the reduction in area, associated with amount of plastic deformation of 0, 38, 57 and 81%, increased in caliber-rolled steels, strain accumulation was observed near interfaces between cementite and ferrite in pearlite structures. Initial pearlite structures were changed to spheroidized cementite and submicron-sized polygonal ferrite by dynamic recrystallization according to the warm caliber rolling process. The initial hypereutectoid steel had a yield strength of 375 MPa, tensile strength of 850 MPa, and elongation of 16.8%. As the rolling strain increased, yield and tensile strength increased dramatically to 1381 and 1604 MPa, respectively. The fracture elongation of the 57% reduction in area (RA) sample decreased to 5.4%. However, it is noteworthy that the total elongation of the 81% RA sample increased slightly to 7.1%. The fatigue limit was also enhanced from 450 MPa for initial hypereutectoid steel to 850 MPa for 81% RA without decreasing the fatigue strength ratio (σfatigue limit/σUTS, 0.53). The 81% RA sample had superior fatigue crack propagation resistance and a high tensile strength–elongation combination compared to that of the initial pearlitic hypereutectoid steel.

In this study, the residual stress reduction through low energy density reheating method in selective laser melting (SLM) process and the correlation between microstructure and mechanical properties were investigated. Inconel 718 superalloy specimens were manufactured via SLM and subjected to reheating (RH) strategies with different energy density, which was based on laser rescanning method. The microstructures were characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The microstructure was observed in the vertical section, parallel to the building direction. With a scanning speed decrease in the RH conditions, the low angle grain boundary (LAGB) and average misoriented region fraction progressively increased. RH conditions exhibited higher Vickers hardness, tensile strength, and yield strength than those of the as-built condition, which increased slightly when the scanning speed was increased. Thermal residual stress was generally higher at z-axis than that at the x-axis. The lowest residual stress value was observed in the highest scanning speed RH condition, and as the scanning speed decreased, it became similar to that of the as-built condition.

High strength Al 7075 alloy was manufactured via twin-roll strip casting (TRC) process, and its microstructure, tensile and fatigue properties were investigated. Commercial Al 7075 alloy fabricated via direct-chill (DC) casting process was also used for comparison. T6 and T651 heat treatments were implemented for both the materials to precipitate MgZn2(η) phases. The TRC alloy showed globular grain shape with η phases evenly distributed at the grain boundary and matrix interior, while the DC alloy showed elongated grains due to hot forging process and η phases clumped together at grain boundaries. The TRC alloy’s yield strength was 518.5 MPa, tensile strength was 578.2 MPa, and elongation was 6.9%. Comparing both the alloys’ mechanical properties, the TRC alloy’s strength was at least about 40 MPa higher and elongation was about 4% lower than the DC alloy. The TRC alloy showed about 20 MPa higher fatigue (fatigue limit) than the DC alloy. The DC alloy was observed to have coarse cracks on fatigue fractured surface. By contrast, the TRC alloy showed uniform fractured surface without coarse cracks, and the evenly-distributed η phases improved fatigue resistance efficiently. The present study sought to examine the correlation among TRC process-led microstructure, tensile and high-cycle fatigue properties while discussing the strengthening mechanism.

Microstructure and wear property of AlSi10Mg alloy manufactured by selective laser melting (SLM) were investigated. Also, the effect of post heat treatment on the mechanical and wear properties was examined. Two kinds of heat treatments (direct aging (DA) and T6) were separately conducted to SLM AlSi10Mg alloy. As-built alloy had a cellular structure formed inside the molten pool. Eutectic Si was also observed at the cellular boundary in as-built alloy. After DA heat treatment, the cellular structure still remained, and a large amount of nano-size Si particles were newly formed inside the cell structure. Both molten pool and cellular structure disappeared, and the size of Si increased in T6 alloy. The values of Vickers hardness measured as 139.4 HV (DA alloy), 128.0 HV (As-built alloy) and 85.1 HV (T6 alloy), respectively. However, concerning to wear property, T6 alloy showed better wear resistance than other alloys. The correlation between microstructure and wear mechanism of SLM AlSi10Mg alloy was also discussed.

The microstructure and macroscopic properties of WC-50Ni+stellite 1(Co-Cr-W, ST1) coating layer fabricated by HVOF spray have been investigated. WC-50Ni powder and ST1 powders were mixed in the ratio of 1:0 and 5:5 wt.%, respectively. Argon heat treatment (Ar) and high-frequency heat treatment (H.F.) were conducted on the coating materials. WC was decomposed in the Ar heat treatment specimen, but decomposition of WC was not observed in the H.F. heat treatment specimen. Hardness was measured for as-sprayed WC-50Ni (821.5Hv) and as-sprayed WC-50Ni+ST1 (668.1 Hv). Hardness of Ar heat treatment specimen was reduced by about 14~18% than that of the as-sprayed coating layers. However, when the H.F. heat treatment was performed, the hardness inversely increased by about 6~10% than the as-sprayed coating layer. Based on these results, the method to improve the mechanical property of HVOF sprayed WC-50Ni+ST1 coating layer has also been also discussed.

An open-cell Ni-Mo-Cr foam was newly manufactured using electrostatic powder spraying process and its room-temperature compressive properties were investigated in this study. For manufacturing Ni-Mo-Cr foam, Ni-Mo-Cr powders were sprayed on the polyurethane pre-form by electrostatic powder spraying process. And then, Ni-Mo-Cr powder sprayed pre-forms were sintered at 1200℃, 1250℃, and 1300℃, respectively. The relative densities of Ni-Mo-Cr foams were measured at 4 ~ 5%. Room temperature compressive curves of ESP Ni-Mo-Cr foams represented the typical compressive 3-stages (elastic, plateau, densification) of open-cell metallic foam. As a result of observation of deformed specimen, the fracture mode found to be changed from brittle to ductile as sintering temperature increased. Based on these findings, correlations between structural characteristics, microstructure, and compressive deformation behavior were also discussed.

This study involves the fabrication of triply periodic minimal surface sheet lattices possessing two different topologies—Neovius and Schoen’s IWP. The structural characteristics of these materials, which were fabricated by laser powder bed fusion using CoCrMo alloy powder, were investigated. The tensile properties and deformation behavior of the materials were evaluated by increasing the unit cell size (1, 2.5, and 5 mm) for each topology. The results of the tensile tests showed that the yield strengths and Young’s moduli of both topologies decreased, and that their elongations increased with decreasing unit cell size. We compared the mechanical properties of the Neovius and IWP lattices, which had the same unit cell size, and found that the former exhibited higher yield strength, tensile strength, and elongation. Further, the tensile deformation behavior of the specimens was analyzed by applying the Gibson–Ashby analytic model. The Neovius lattice accommodated more uniform deformations in a greater number of cell layers. These experimental observations and the use of a simplified model of the lattice structure can enhance the understanding of the mechanism of the room-temperature tensile deformation of Neovius and IWP sheet-based lattice structures.

Recently, attempts have been made to use porous metal as catalysts in a reactor for the hydrogen manufacturing process using steam methane reforming (SMR). This study manufactured Ni-Cr-Al based powder porous metal, stacked cubic form porous blocks, and investigated high temperature random stack creep property. To establish an environment similar to the actual situation, a random stack jig with a 1-inch diameter and height of 75 mm was used. The porous metal used for this study had an average pore size of ~1161 μm by rolling direction. The relative density of the powder porous metal was measured as 6.72%. A compression test performed at 1073K identified that the powder porous metal had high temperature (800°C) compressive strength of 0.76 MPa. A 800°C random stack creep test at 0.38 MPa measured a steady-state creep rate of 8.58×10–10 s–1, confirming outstanding high temperature creep properties. Compared to a single cubic powder porous metal with an identical stress ratio, this is a 1,000-times lower (better) steady-state creep rate. Based on the findings above, the reason of difference in creep properties between a single creep test and random stack creep test was discussed.

This study manufactured a SiC coating layer using the vacuum kinetic spray process and investigated its microstructure and wear properties. SiC powder feedstock with a angular shape and average particle size of 37.4 μm was used to manufacture an SiC coating layer at room temperature in two different process conditions (with different degrees of vacuum). The thickness of the manufactured coating layers were approximately 82.4 μm and 129.4 μm, forming a very thick coating layers. The SiC coating layers consisted of α-SiC and β-SiC phases, which are identical to the feedstock. Cross-sectional observation confirmed that the SiC coating layer formed a dense structure. In order to investigate the wear properties, ball crater tests were performed. The wear test results confirmed that the SiC coating layer with the best wear resistance achieved approximately 4.16 times greater wear resistance compared to the Zr alloy. This study observed the wear surface of the vacuum kinetic sprayed SiC coating layer and identified its wear mechanism. In addition, the potential applications of the SiC coating layer manufactured using the new process were also discussed.

This study stacked a thin, dense BCuP-5 (Cu-Ag-P based filler metal) on a Cu-plate using the laser cladding (L.C) process to develop a method to manufacture Ag reducing multilayer clad electrical contact material with an Ag-M(O)/Ag/Cu/BCuP-5 structure. Then, the microstructure and macroscopic properties of the manufactured BCuP-5 coating layer were analyzed. The thickness of the manufactured coating layer was approximately 1.7 mm (maximum). Microstructural observation of the coating layer identified Cu, Ag and Cu-Ag-Cu3P ternary eutectic phases like those in the initial BcuP-5 powder. To evaluate the properties of the manufactured coating layer, hardness and adhesion strength tests were performed. The average hardness of the laser cladded coating layer was 183.2 Hv, which is 2.6 times greater than conventional brazed BcuP-5. The average pull-off strength measured using the stud pull test was 341.6 kg/cm2. Cross-sectional observation of the pulled-off material confirmed that the coating layer and substrate maintained a firm adhesion after pull-off. Thus, the actual adhesion strength of Cu/BcuP-5 was inferred to be greater than 341.6 kg/cm2. Based on the above findings, it was confirmed that it is possible to manufacture a sound Ag reducing multilayer clad electrical contact material using the laser cladding process.

This study investigated the microstructure and high temperature oxidation properties of Fe-25Cr-20Ni-1.5Nb, HK30 alloy manufactured by metal injection molding (MIM) process. The powder used in MIM had a bi-modal size distribution of 0.11 and 9.19 μm and had a spherical shape. The initial powder consisted of γ-Fe and Cr23C6 phases. Microstructural observation of the manufactured (MIMed) HK30 alloy confirmed Cr23C6 along the grain boundary of the γ-Fe matrix, and NbC was distributed evenly on the grain boundary and in the grain. After a 24-hour high temperature oxidation test at air atmospheres of 1000, 1100 and 1200°C, the oxidation weight measured 0.72, 1.11 and 2.29 mg/cm,2 respectively. Cross-sectional observation of the oxidation specimen identified a dense Cr2O3 oxide layer at 1000°C condition, and the thickness of the oxide layer increased as the oxidation temperature increased. At 1100°C and 1200°C oxidation temperatures, Fe-rich oxide was also formed on the dense Cr2O3 oxide layer. Based on the above findings, this study identified the high-temperature oxidation mechanism of HK30 alloy manufactured by MIM.

This study investigated the effect of T6 heat treatment on the microstructure and scratch wear behavior of hypoeutectic ­Al-12wt.%Si alloy manufactured by extrusion. Microstructural observation identified spherical eutectic Si phases before and after the heat treatment of alloys (F, T6). Phase analysis confirmed Al matrix and Si phase as well as Al2Cu and Al3Ni, Mg2Si in both alloys. In particular, Al2Cu was finer and more evenly distributed in T6 alloy. This resulted in Vickers hardness of T6 alloy that was 2.3 times greater compared to F alloy. The scratch wear test was conducted using constant load scratch test (CLST) mode and multi-pass scratch test (MPST) mode. The scratch coefficient and worn out volume obtained by such were used to evaluate wear properties before and after heat treatment. In the case of T6 alloy, its scratch coefficient was lower than F alloy in all load ranges. After 15 repeated tests to measure worn out volume, F alloy and T6 alloy measured 1.2×10–1 mm3 and 7.8×10–2 mm3, respectively. In other words, the wear resistance of T6 alloy were confirmed to be better than those of F alloy. In addition, this study attempted to identify the microstructural factors that contribute to the better scratch wear resistance of T6 alloy and wear mechanism from surface and cross-section observations after the wear tests.

The metallic glass powder of newly designed Fe46.8-Mo30.6-Cr16.6-C4.3-B1.7 composition was employed to fabricate Fe-based metallic glass coating layers using representative thermal spray processes, viz. atmospheric plasma (plasma), HVOF and vacuum plasma spray (VPS). The microstructure and wear properties of the thermal sprayed Fe based metallic glass coating layers were investigated. XRD analysis results showed that all the three coating layers had broad halo peaks. Alloying element depletion was observed in the coating layer in the vicinity of the oxides. However, the VPS coating layer showed no depletion area. Wear test results showed that the VPS coating layers had the best wear resistance among all the three coating layers, whereas the plasma material had the poorest wear resistance property. Worn surface and cross-section observation revealed that the plasma material had particle boundary delamination because of its lower bonding force between the particles. Directly below the worn-out surface of the HVOF coating layers, microcracks were generated along the particle boundaries. By contrast, no defects were found at all directly under the worn-out surface of the VPS materials. The wear behavior of Fe based metallic glass coating layers fabricated in diverse thermal spray processes was discussed with respect to the microstructure.

In this study, we investigate the influence of Sc microalloying on the microstructure of the Al5083 alloy. Trace amounts of Sc addition drastically improve the mechanical properties of the Al5083 alloy from 216 MPa to 233 MPa. Macroscopically, the addition of Sc significantly reduces the grain size of Al by approximately 50%. Additionally, a microstructural investigation reveals that the Sc microalloying element induces fine Al3Sc nanoprecipitates in the Al matrix. The formation of Al3Sc nanoprecipitates results in a pinning effect on the dislocations, leading to accumulated dislocations. Compared to a Sc-free Al5083 alloy specimen, the number density of dislocations in the Sc-added Al5083 alloy significantly increases after hot rolling, enhancing the tensile properties. We reveal that the improved mechanical properties of Al5083 with Sc microalloying originate from the grain refinement and the formation of fine Al3Sc nanoprecipitates.

Contact materials in high-voltage vacuum interrupters require properties such as high conductivity, density and hardness to minimize arc heat damage. In this study, Cu–Cr–Mo alloy contact materials were examined for their usage as high-voltage contact materials. Ball milling was performed after analyzing the raw materials of the Cu, Cr and Mo powders. A green compact was produced using high pressure with a mixed powder. Subsequently, the composite was produced by sintering via the temperature and infiltration method according to the Cu content in the green compact. The composite sintering method produced a density of 8.55 g/cm3 (relative density 93%), a hardness of 217 HV and an electrical conductivity of 40.7% IACS at 1200 °C. The composite of 10 wt.% Cu produced by the Cu infiltration method exhibited a density of 8.7 g/cm3 (relative density 94%), hardness of 274 HV and electrical conductivity of 39 IACS% at 1300 °C. The measurements of the physical properties of our newly established method demonstrated a new possibility of using the Cu–Cr–Mo alloy as a contact material for high-voltage vacuum interrupters.