This study explores the profound impact of varying oxygen content on microstructural and mechanical properties in specimens HO and LO. The higher oxygen concentration in specimen HO is found to significantly influence alpha lath sizes, resulting in a size of 0.5-1 μm, contrasting with the 1-1.5 μm size observed in specimen LO. Pore fraction, governed by oxygen concentration, is high in specimen HO, registering a value of 0.11%, whereas specimen LO exhibits a lower pore fraction (0.02%). Varied pore types in each specimen further underscore the role of oxygen concentration in shaping microstructural morphology. Despite these microstructural variations, the average hardness remains consistent at ~370 HV. This study emphasizes the pivotal role of oxygen content in influencing microstructural features, contributing to a comprehensive understanding of the intricate interplay between elemental composition and material properties.

The CoCrFeMnNi high-entropy alloy (HEA), which is the most widely known HEA with a single facecentered cubic structure, has attracted significant academic attention over the past decade owing to its outstanding multifunctional performance. Recent studies have suggested that CoCrFeMnNi-type HEAs exhibit excellent printability for selective laser melting (SLM) under a wide range of process conditions. Moreover, it has been suggested that SLM can not only provide great topological freedom of design but also exhibit excellent mechanical properties by overcoming the strength–ductility trade-off via producing a hierarchical heterogeneous microstructure. In this regard, the SLM-processed CoCrFeMnNi HEA has been extensively studied to comprehensively understand the mechanisms of microstructural evolution and resulting changes in mechanical properties. In this review, recent studies on CoCrFeMnNi-type HEAs produced using SLM are discussed with respect to process-induced microstructural evolution and the relationship between hierarchical heterogeneous microstructure and mechanical properties.

Zintl phase Mg3Sb2 is a promising thermoelectric material in medium to high temperature range due to its low band gap energy and characteristic electron-crystal phonon-glass behavior. P-type Mg3Sb2 has conventionally exhibited lower thermoelectric properties compared to its n-type counterparts, which have poor electrical conductivity. To address these problems, a small amount of Sn doping was considered in this alloy system. P-type Mg3Sb2 was synthesized by controlled melting, pulverizing, and subsequent vacuum hot pressing (VHP) method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate phases and microstructure development during the process. Single phase Mg3Sb2 was successfully formed when 16 at.% of Mg was excessively added to the system. Nominal compositions of Mg3.8Sb2-xSnx (0 ≤ x ≤ 0.008) were considered in this study. Thermoelectric properties were evaluated in terms of Seebeck coefficient, electrical conductivity, and thermal conductivity. A peak ZT value ≈ 0.32 was found for the specimen Mg3.8Sb1.994Sn0.006 at 873 K, showing an improved ZT value compared to intrinsic one. Transport properties were also evaluated and discussed.

In this study, an AISI 316 L alloy was manufactured using a selective laser melting (SLM) process. The tensile and impact toughness properties of the SLM AISI 316 L alloy were examined. In addition, stress relieving heat treatment (650oC / 2 h) was performed on the as-built SLM alloy to investigate the effects of heat treatment on the mechanical properties. In the as-built SLM AISI 316 L alloy, cellular dendrite and molten pool structures were observed. Although the molten pool did not disappear following heat treatment, EBSD KAM analytical results confirmed that the fractions of the low- and high-angle boundaries decreased and increased, respectively. As the heat treatment was performed, the yield strength decreased, but the tensile strength and elongation increased only slightly. Impact toughness results revealed that the impact energy increased by 33.5% when heat treatment was applied. The deformation behavior of the SLM AISI 316 L alloy was also examined in relation to the microstructure through analyses of the tensile and impact fracture surfaces.

Additively manufactured metallic components contain high surface roughness values, which lead to unsatisfactory high cycle fatigue resistance. In this study, high cycle fatigue properties of selective laser melted Ti-6Al- 4V alloy are investigated and the effect of dry-electropolishing, which does not cause weight loss, on the fatigue resistance is also examined. To reduce the internal defect in the as-built Ti-6Al-4V, first, hot isostatic pressing (HIP) is conducted. Then, to improve the mechanical properties, solution treatment and aging are also implemented. Selective laser melting (SLM)-built Ti64 shows a primary α and secondary α+β lamellar structure. The sizes of secondary α and β are approximately 2 μm and 100 nm, respectively. On the other hand, surface roughness Ra values of before and after dry-electropolishing are 6.21 μm and 3.15 μm, respectively. This means that dry-electropolishing is effective in decreasing the surface roughness of selective laser melted Ti-6Al-4V alloy. The comparison of high cycle fatigue properties between before and after dry-electropolished samples shows that reduced surface roughness improves the fatigue limit from 150 MPa to 170 MPa. Correlations between surface roughness and high cycle fatigue properties are also discussed based on these findings.

In this study, the glass melting properties are evaluated to examine the possibility of using refused coal ore as replacement for ceramic materials. To fabricate the glass, refused coal ore with calcium carbonate and sodium carbonate in it (which are added as supplementary materials) is put into an alumina crucible, melted at 1,200 ~ 1,500℃ for 1 hr, and then annealed at 600℃ for 2 hrs. We fabricate a black colored glass. The properties of the glass are measured by XRD (X-ray diffractometry) and TG-DTA (thermogravimetry-differential thermal analysis). Glass samples manufactured at more than 1,300℃ with more than 60 % of refused coal ore are found by XRD to be non-crystalline in nature. In the case of the glass sample with 40 % of refused coal ore, from the sample melted at 1,200℃, a sodium aluminum phosphate peak, a disodium calcium silicate peak, and an unknown peak are observed. On the other hand, in the sample melted at 1,300℃, only the sodium aluminum phosphate peak and unknown peak are observed. And, peak changes that affect crystallization of the glass according to melting temperature are found. Therefore, it is concluded that glass with refused coal ore has good melting conditions at more than 1,200℃ and so can be applied to the construction field for materials such as glass tile, foamed glass panels, etc.

In order to investigate ice melting properties of road deicers with chemical types, theoretical comparison using performance index (PI) [1] and experimental analysis were carried out. In the theoretical comparison using PI, differences in melting ice performance properties were shown with chemical types and temperature ranges. Sodium chloride (NaCl) showed the best melting performance at -1.5~-3.5℃, but lower PI than other chemicals (CaCl2 and MgCl2) at lower temperature than -4.5℃. Calcium chloride (CaCl2) showed the best PI at lower than - 6.5℃, and at higher than -1.5℃, but the lowest PI at -1.5~-4.5℃. Magnesium chloride (MgCl2) showed the best performance at -3.5~-6.5℃, but the lowest PI at higher temperature than -1.5℃. PI can be regarded as a representative index for melting ice performance of liquid deicer, however, it is not enough to evaluate that of solid deicer, because the effect of heat of solution is not considered in PI. In the experimental analysis, comparison for ice melting performance between solid and liquid deicers was mainly carried out. Solid calcium chloride showed very good persistency and quick-acting property by the effect of heat of solution. Solid sodium chloride has no quick-acting property, but very good persistency at a mild temperature (-3℃), whereas ice melting performance declined greatly at severely low temperature (-11℃). Liquid sodium chloride and calcium chloride showed somewhat good quick-acting property, but inferior persistency to solid ones.

For the development of a low-melting point filler metal for brazing aluminum alloy, we analyzed change of melting point and wettability with addition of Sn into Al-20Cu-10Si filler metal. DSC results showed that the addition of 5 wt% Sn into the Al-20Cu-10Si filler metal caused its liquidus temperature to decrease by about 30 oC. In the wettability test, spread area of melted Al-Cu-Si-Sn alloy is increased through the addition of Sn from 1 to 5 wt%. For the measuring of the mechanical properties of the joint region, Al 3003 plate is brazed by Al-20Cu-10Si-5Sn filler metal and the mechanical property is measured by tensile test. The results showed that the tensile strength of the joint region is higher than the tensile strength of Al 3003. Thus, failure occurred in the Al 3003 plate.

Ni-doped was prepared by the encapsulated induction melting and hot pressing, and its doping effects on the thermoelectric properties were investigated. Single phase was successfully obtained by the subsequent heat treatment at 773K for 24 hours. Nickel atoms acted as electron donors by substituting cobalt atoms. Thermoelectric properties were remarkably improved by the appropriate doping.

The encapsulated induction melting and hot pressing were employed to prepare Fe-doped skutterudites and their thermoelectric properties were investigated. Single phase was successfully obtained by the subsequent heat treatment at 773K for 24 hours. Iron atoms acted as electron acceptors by substituting cobalt atoms. Thermoelectric properties were remarkably improved by the appropriate doping. was found as an optimum composition for best thermoelectric properties in this work.

Powder mine wastes cause secondary environmental problems from dust flying around villages. It is necessary to recycle to prevent this secondary pollution and to use its beneficial contents. Magnesium and iron may play a role like that of aluminum in geopolymer forming. In this study, therefore, we analyzed the compressive strength of geopolymer prepared from melting slag (MS) and high-magnesium iron mine waste (MW). The compressive strength increased by increasing the mixing ratio of MS and decreasing the L/S ratio. The optimal properties were obtained at a mixing ratio of MS to MW of 5 : 5, molar ratio of SiO2/Na2O of 1.8, and L/S ratio of 0.2. Under these conditions, the compressive strength at 28 days was 112.5 MPa. According to the FT-IR analysis, a geopolymer structure was identified. As a result, we confirmed the possibility of geopolymer forming from MS and MW.

In this work, lightweight brick was prepared from aluminum dross, MS and MBA. Aluminum dross is discharged as by-product through the process of aluminum smelting. It can be used as foaming agent, because it produces hydrogen gas due to the reaction with alkali activator. In this study, the specific gravity and compressive strength of prepared brick was discussed with the addition of aluminum dross. Compressive strength, flexural strength and specific gravity was 36 MPa, 2.6 MPa and 1.48 at mixing ratio of 0.9wt% aluminum dross, respectively. The physical property of brick was debased with the addition of aluminum dross. Because the pore size was bigger in accordance with the addition of aluminum dross.