Modulation of Co-depleted zone and shear strength of YG18/40Cr joints by pre-plated Co layer on YG18 surface

Abstract

The multi-layer composite filler metal (YG18 surface pre-plated with Co layer + Ag–Cu–In–Ti filler metal) was designed in this study. The mechanism of modulation of Co-depleted zone and shear strength of joints by Co plating was elucidated. A more significant Co-rich layer existed around the WC particles, meanwhile, the presence of plastical Ag–Cu–In ternary eutectic between the TiCo layer and the YG18/TiC layer relieved the joint stress and ensured that no cracks were generated in the TiCo layer. Under the condition that the width of the Co-depleted zone was smaller (less than 3 μm), the presence of the dispersed Ti2Cu particles surrounded by the plastic phases ternary eutectic and Cu [s, s] in the filler layer was superior in terms of preventing crack propagation and absorbing the stress concentration. The best modulation of the filler layer microstructure and the Co-depleted zone was achieved when the pre-plated Co layer was around 2.5 μm. The Co-depleted zone was reduced by 50%, and the shear strength of joints was increased by 49% to 291 MPa. The results of the study provide a new way to design new multilayer composite filler metal.