Mechanical and Microstructural Characterization of the Bond Interface Formed in Diffusion Welding of CoCrNi Medium Entropy Alloy (MEA) and AISI 304 Stainless Steel Under Various Processing Parameters

CoCrNi medium entropy alloy (MEA) recently gained a lot of attention from the scientific community due to its excellent mechanical properties at cryogenic temperatures. AISI 304 stainless steel is also a commonly used material in cryogenic environments. Therefore, the main objective of this research was to join CoCrNi MEA with AISI 304 stainless steel to obtain combinatorial properties for cryogenic applications. Vacuum diffusion welding process was utilized under different processing parameters. Three levels of welding temperatures and bonding time were selected and the influence of these parameters were investigated using microstructural characterization. Electron microprobe analysis, electron backscattered diffraction, and SEM with EDX analysis were used in the analysis of bond interface regions. At low welding temperature and time, weld discontinuities were formed which were drastically suppressed when both the parameters increased. Formation of IMCs was also found along with the bond interface and was significantly reduced upon increasing welding temperature and bonding time. Moreover, at higher parametric values thick bond interface was formed and it was concluded that its development was mainly due to the diffusion of Fe atoms. The quality of the bond interface was determined through shear testing and its fractography was also executed to correlate the processing parameters with the joint's shear strength. Diffusivities and activation energies of the constituent elements were also calculated.