Evolution of Bonding Interface during Ultrasonic Welding between Ni and Steels with Various Microstructure

Abstract

In this study, Ni was bonded with steels having various microstructures to investigate the effect of various microstructures in steels on the bonding strength evolution by ultrasonic welding. It is found that at Ni/ferrite interface having similar hardness, the bonding can be produced by flattening of wear particles generated from the abrasion during ultrasonic welding to obtain a higher degree of plastic deformation, which is positive to bonding strength evolution. As for Ni/pearlite and Ni/martensite interfaces having dissimilar hardness, the bonding formation is difficult due to the presence of hard phases that limit the degree of plastic deformation near the interface, and Ni fragments are attached on the steel side. As a result, lower bonding strength evolution is correspondingly obtained due to slower increment of bonded area, whereas longer time is required for bonding formation between attached Ni fragments and the base metal Ni.