Dissimilar electron beam welding of the medium-entropy alloy (NiCoCr)94Al3Ti3 to 304 stainless steel

Electron beam welding of the medium-entropy alloy (MEA) (NiCoCr)94Al3Ti3 to 304 stainless steel (SS) has been undertaken. Defect-free joints were obtained with coarse columnar grains: the columnar grains on the 304 SS side of the fusion zone (FZ) were finer (94 μm, length-to-width ratio∼2.7) than the grains on the MEA side (204 μm, 2.9), a difference that probably resulted from a higher cooling rate after welding due to the higher thermal conductivity of the 304 SS compared to the MEA. Mixing of the two materials in the FZ led to lower vol.% (14%) and larger diameter (44 nm) of L12 nanoparticles compared to the 23 nm dia. and 37% vol.% in the aged MEA, a result consistent with CALPHAD analysis. The joint showed a good combination of yield strength (323 MPa), ultimate tensile strength (670 MPa), and elongation (24%). Failure occurred by ductile fracture in the FZ.