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Multiple principal element alloys (MPEA) encompass the well-known high entropy alloys (HEAs). MPEA/HEA represent a new class of materials consisting of at least three alloying elements, each containing 5 to 35 at.-%. This alloying concept thus differs fundamentally from conventional materials such as steel or nickel alloys. For this purpose, the alloying elements are specifically selected, and the microstructures are adjusted in a single-phase and, in some cases, multi-phase manner. In particular, conflicting goals, such as the trade-off between strength and ductility in conventional steels, are overcome. In the last 20 years, however, the focus has been on material synthesis. With the increase in available material quantities, the focus is now on pro-cessing issues such as joining and welding processes. The weldability of MPEA has received very little atten-tion so far. Experience with dissimilar metal welds (DMWs) is completely lacking but is essential for the appli-cation of these materials in combination with conventional materials. The present study presents, comprehen-sive experimental results on the weldability of MPEA-DMWs. For that purpose, a Co20Cr20Fe20Mn20Ni20 HEA in cold-rolled and heat-treated condition was joined by means of tungsten inert gas welding (TIG) with the austenitic Cr-Ni steel AISI 304. The DMWs resulted in interesting mechanical properties. They were obtained by instrumented tensile tests as well as the local deformation in the weld area by using digital image correlation (DIC) technique. A significant softening in the heat-affected zone (HAZ) of the MPEAs as well as a slightly reduced tensile strength with a significant decrease of the elongation at fracture were found. The experiments provided proof in principle of the weldability of the MPEAs for DMWs with conventional materials that ensure a corresponding capability for mechanical loading. This allows further considerations on the application of these innovative materials.
Dissimilar metal TIG weld joints of multiple principal element alloys (MPEA) to austenitic steel 304
(2023)
Multi-element alloys (MPEA - Multiple Principal Element Alloys) represent a new class of materials consisting of at least three alloying elements, each with 5 to 35 atomic %. This material class includes high-entropy alloys (HEA, with n ≥ 4 elements). The underlying alloying concept differs fundamentally from conventional materials such as the Fe-based steel. For this purpose, the alloying elements are specifically selected, and the microstructures are adjusted in a single-phase and, in some cases, multi-phase manner. The aim is to identify highly innovative MPEA with individually adjustable properties for industrial applications. In the last 20 years, however, the focus has been on pure material synthesis. With the increase in available material quantities, the focus is on processing issues such as joining and welding processes. In that connection, the weldability of MPEAs has received very little attention so far. Experience with dissimilar metal welds (DMWs) is completely lacking but is essential for the application of these materials if joint to conventional materials. This study presents selected experimental results on the weldability of MPEA-DMWs and the resulting microstructures. For this purpose, the equiatomic CoCrFeMnNi (HEA) was investigated in cold-rolled (CR) and heat-treated (HT) condition and joined by tungsten inert gas (TIG) welding to an austenitic stainless steel 304. The DMWs showed defect-free conditions (no lack of fusion, cracks and so on), whereas the cold-rolling increases the microhardness. The global mechanical properties were obtained by instrumented tensile tests of cross-weld samples and showed sufficient yield and tensile strength comparable to that of the individual base materials (BM). The local strain conditions were determined by digital image correlation and showed the highest local strains to occur in the intermixed weld metal. Indeed, the preferred fracture location of the cross-weld tensile samples was in the weld metal. Finally, the experiments proofed the weldability of the MPEAs to conventional 304. This enables targeted further considerations for example as structural materials.