Diffusion welding of CoCrNi medium entropy alloy (MEA) and SUS 304 stainless steel at different bonding temperatures

This research work was mainly concerned to investigate the effect of bonding temperature on the weldability of CoCrNi MEA with SUS 304 stainless steel. Shear test and nano hardness measurements were used to evaluate the mechanical performance of the welded joints. The formation of IMCs intensified along with the bond interface when samples were treated at low bonding temperature (i.e., 925 °C) which badly affected the joint’s shear strength. Reduction in IMCs formation transpired as the bonding temperature increase, and eventually, the formation of the solid solution was instigated at the bond interface. Furthermore, at 1075 °C bonding temperature, the bond interface was almost free from IMCs and transformed to a solid solution, triggering the enhancement of the joint’s shear strength. SEM with EDX, XRD, and thermal analysis was used for microstructural examination to comprehend the interface reaction/bond formation mechanism during the welding process. Moreover, a thermodynamic description is also provided to predict the phase formation at the bond interface. In this regard, established rules (i.e., ΔH_mix, ΔS_mix, Ω, and δ) to determine the phase stability of HEAs were implemented which found valid in predicting the phase formation at the bond interface.