Interfacial microstructure and shear strength of Ti6Al4V alloy/316 L stainless steel joint brazed with Ti33.3Zr16.7Cu50-xNix amorphous filler metals

Ti33.3Zr16.7Cu50-xNix (x = 0-16.5, at%) amorphous filler metals were designed to braze Ti6Al4V alloy and 316 L stainless steel (SS). The effect of Ni addition in filler metals on the wettability, joint microstructure evolution and shear strength were investigated. The reaction phase identification and crack initiation mechanism were analyzed in depth. Ni addition weakened the wettability of the filler metal and thickened the brazed seam. The filler metal with 11 at.% Ni was optimized for brazing of Ti6Al4V alloy/316 LSS with the maximum joint shear strength of 318 MPa, FeTi, Fe2Ti, FeCr, and alpha-Fe phases formed around the transition zone close to 316 L SS substrate, which was the weak part of the brazed joints. The interface between Fell and Fe2Ti phases was non-coherent with the lattice mismatch of 61.4%, initialing the crack at (beta-Ti + FeTi)/Fe2Ti interface. The initiative cracks mainly propagated along the Fe2Ti and FeCr layers with brittle feature. Optimizing the constituents and alloying process for Ti-Cu-based filler metal has huge potential in improving the performance of titanium alloy/steel joint. (C) 2019 The Authors. Published by Elsevier Ltd.