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This study investigates the gas tungsten arc (GTA) weldability of austenitic stainless steel (STS) 304 using STS 308L and high-entropy alloy (HEA) fillers and its applicability in cryogenic environments. Because the grain sizes of both weld metals (WMs) were coarser than those of base metal (BM), and all WMs have a few phase transformations, the tensile properties of all WMs were worse than that of the BM. However, the tensile strength and elongation of HEA weld at 77 K increased simultaneously than those at 298 K, whereas the elongation of STS 308L weld decreased at 77 K than that at 298 K. All WMs exhibited excellent tensile strengths at 77 K, attributable to martensite transformations and deformation twins, respectively.

This study investigates the gas tungsten arc (GTA) weldability of austenitic stainless steel (STS) 304 using STS 308L and high-entropy alloy (HEA) fillers and its applicability in cryogenic environments. Because the grain sizes of both weld metals (WMs) were coarser than those of base metal (BM), and all WMs have a few phase transformations, the tensile properties of all WMs were worse than that of the BM. However, the tensile strength and elongation of HEA weld at 77?K increased simultaneously than those at 298?K, whereas the elongation of STS 308L weld decreased at 77?K than that at 298?K. All WMs exhibited excellent tensile strengths at 77?K, attributable to martensite transformations and deformation twins, respectively.

Abstract: Power semiconductors require a large bonding area for die attachment. For this purpose, transient liquid phase bonding (TLPB) was applied using fabricated interlayers, namely Sn–3Cu and Sn–10Cu, to study the intermetallic compound (IMC) formation, and the results were compared with those obtained with a pure-Sn interlayer. The Sn–3Cu and Sn–10Cu interlayers exhibited primary IMC fraction of 0.06 and 0.24, respectively, before the TLPB. For a Cu/interlayer/Cu sandwich structure, the TLPB was applied at 250 °C over various time periods (1–4 h). A reduction in the bonding time was more significant for a Sn–10Cu interlayer with a larger amount of primary IMCs than for the Sn–3Cu interlayer. The time exponent of the IMC fraction with respect to the bonding time was approximately 0.3 for all interlayers. This implies that the IMC growth mechanism is governed by a liquid channel or wet grain boundary diffusion. The nearly constant fraction and increasing size of the primary IMCs produced during the TLPB indicate that the primary IMCs coalesced during this process. The primary IMCs preferentially coalesced with the interface IMCs produced during the TLPB when they had the same crystalline orientation. Graphic Abstract:

The broad potential applications of ferritic stainless steel in industry can be increased with the addition of protective elements such as carbon for surface hardening. Laser surface hardening (LSH) using carbon elements, such as graphite, has received widespread attention. However, to obtain high quality results, the use of graphite slurry, a specific environment, or remelting are required. To overcome this challenge, the LSH using graphene as an alternative to graphite was comparatively studied in this work. Accordingly, the stability of hardened layers, which depicts their sustainability in actual environmental conditions, was compared in graphene, graphite, and their slurries to improve the evaluation of graphene in the LSH process. The stability of hardened layers predominantly depends on the hardness, crack susceptibility, interfacial stress, hardness depth (or aspect ratio), and interfacial hardness. Under suitable process conditions, graphene exhibits good stability, with the highest hardness and low stress fluctuation without crack formation at the interface. Moreover, the powder layer thickness and laser power can be adjusted to achieve maximum improvements in the aspect ratio and microhardness in the area near the interface. Thus, high microhardness and a crack-free hardened layer without additional remelting or the use of a slurry were obtained.