This study investigated the hardness and microstructure of dual-phase (DP780) steel as a function of temperature and examined the effect of tempering temperature on the microstructure and mechanical properties of DP steel. The aim was to explore the changes in mechanical properties that rely on heat treatment when processing high-strength steel, widely used in the automotive industry. The dual-phase microstructure, composed of ferrite and martensite phases, showed variations in phase fractions with tempering temperature. Specifically, the hardness decreased up to 600℃, then increased above 600℃, with the lowest hardness observed at 600℃. This is attributed to the recovery and martensite decomposition caused by low-temperature tempering, leading to a decrease in hardness. Above 600℃, the formation of new martensite resulted in increased hardness. Therefore, high-strength steel with a dual-phase microstructure like DP780 is significantly affected by the martensite fraction resulting from tempering during processing, which has a substantial impact on its mechanical properties.

In this study, the effect of zirconium to commercial Al-Si-Cu alloy on the microstructure and mechanical properties was investigated. The test specimens of Zr addition were prepared by gravity casting with commercialized Al₁₂Si₂Cu, Al₆Si₂Cu, and Al₁₀Zr master alloys up to 1 wt.%. The cast ingot was subjected to solution treatment at 495℃ for 4 h and then aged at 190℃ for T6 heat treatment. The secondary dendrite arm spacing (SDAS) of the alloy increased as the amount of Zr addition increased, and the primary (Al,Si)₃(Zr,Ti) phase was generated. The hardness decreased with the increase in SDAS. Precipitation of the Zr-rich phase in the Al matrix after T6 heat treatment was observed by EPMA (electron probe micro-analzer), EDS (energy dispersive spectroscopy), and XRD (X-ray diffraction) bulk-extraction. Consequently, The generation of Zr-rich phase with the addition of Zr in Al-Si-Cu alloy would be a successful hardening phenomenon in Al alloy.

The aim of the present study is to verify the microstructural and mechanical properties of Ta-Zr dissimilar metals welded using TIG welding. Due to the significant differences in thermo-mechanical properties, microstructures were observed across the weld zone. The HAZ exhibited grain coarsening, while the Zr-side HAZ showed significant Ta diffusion. The fusion zone (FZ) displayed cellular and equiaxed structures. Hardness tests indicated a higher hardness in the FZ due to solid solution strengthening and spinodal decomposition. Tensile tests revealed fracture in the Ta-side HAZ, caused by shrinkage defects and brittle Ta oxides. Fracture surface analysis showed brittle patterns, highlighting the need for defect control in dissimilar Ta-Zr welds.

This work was intended to comparatively investigate the hardness and thermal conductivities of Mg-9%Al-1%Zn (wt%) alloy having fully discontinuous precipitates microstructure obtained by continuous cooling after solution treatment(designated as "DPs-CC") and T6 heat-treated microstructure, respectively. The T6 microstructure was distinctively characterized by two regions of (i) discontinuous precipitates showing (α + β) lamellar morphology and (ii) finely distributed continuous precipitate particles. The DPs-CC microstructure had various (α + β) lamellar spacings due to different transformation temperatures during continuous cooling. The T6 microstructure exhibited slightly higher hardness than the DPs-CC one, resulting from the lower (α + β) interlamellar spacing of the discontinuous precipitates and the fine distribution of continuous precipitates. It is noticeable that the DPs-CC microstructure possessed 98.2% level of thermal conductivity between RT and 200℃ compared to the T6 microstructure. The XRD analyses suggest that similar level of Al concentration in α-(Mg) matrix may well be responsible for the almost identical thermal conductivities for the T6 and DPs-CC microstructures.

In this study, to address the recent increasing demand for high-entropy alloys, an economical high-entropy alloy was fabricated and the mechanical properties and corrosion behavior of the fabricated alloy were studied. By reducing the contents of relatively expensive elements, Co and Ni, and increasing the proportion of inexpensive alloying element, Fe, in a high-entropy alloy of the Al_0.3CrCuCo_xFe_yNi_3-x-y system, an economical high-entropy alloy with excellent mechanical properties was fabricated. The mechanical properties and corrosion behavior of the Al_0.3CrCuCo_xFe_yNi_3-x-y high-entropy alloys were evaluated by using nanoindentation tests, Vickers hardness tests, and potentio-dynamic polarization experiments. The analysis results showed that replacing Ni and Co with Fe improved the mechanical properties without decreasing the corrosion resistance. It is expected that high-entropy alloys with excellent mechanical properties and improved economic feasibility can be fabricated by utilizing this.

In this study, the strength enhancement of Meso20 alloy, which is a P/M7000 series aluminum alloy. The effect on the precipitation process and mechanical properties was investigated by focusing on the phases precipitated during the heating maintenance and high-temperature extrusion of the powder after CIP (cold isostatic pressing) molding. Changes in the precipitation process were investigated when the amounts of Mn and Cu were changed. After solution heat treatment at 763 K for 7.2 ks, and then isothermal aging at 383 K for 108 ks, precipitates in the specimen are of two types: a rod-shaped compound and a massive of Al₆Mn. As a result of observation using SEM, the atomized powder of Meso20 before heating was a cell shaped structures. In the specimen quenched after heat treatment at 773 K for 3.6 ks, rod-shaped pre cipitates (Q phase) and massive precipitates (Al₆Mn) were observed. As a result of EPMA analysis, large amounts of Mg, Zn, and Cu were included, and the average cell size was 2.6 ㎛, and the average width of the segregation layer was 130 nm. When the amount of Cu was kept constant and the amount of Mn was increased from 4 mass% to 7 mass%, the Al₆Mn precipitation amount increased, and both the compressive strength and the plastic elongation decreased. When the amount of Mn was kept constant and the amount of Cu was increased from 0.5 mass% to 2.5 mass%, the amount of Q phase precipitation increased.

The MoS₂ (molybdenum disulfide) has been recognized as a representative 2D materials in the transition metal dichalcogenides group, exhibiting significant potential for electrical, optical, wear-resistance applications. With the growing demand on continuous and uniform quality of MoS₂ thin films for the industrial application, feasible techniques are being explored, and the sputtering is emerging as one of the noticeable candidate to replace CVD (chemical vapor deposition) and ALD (atomic layer deposition) processes which has relatively been studied due to its easy process control. Accordingly, the main aim of this study is to investigate the effects of process variables on structural and material properties of MoS₂ thin films deposited on a 1 × 1 inch of SiO₂/Si substrate by 13.56 MHz RF (radio frequency) sputtering methods using a single MoS₂ target through Raman spectroscopy, SEM (scanning electron microscopy) and EDS (energy dispersive spectroscopy) mapping analysis. All of the deposited MoS₂ thin films were composed of flower-like nanostructures exhibiting columnar arrays and their size showed a larger tendency as the plasma power increased and the process pressure decreased. Additionally, the deposition rate revealed a proportional relationship with sputtering time, reaching approximately 40 nm/min under optimized process conditions.