Grain boundary migration behavior and microstructure evolution during multilayer additive hot-compression bonding

Abstract

Multilayer additive hot-compression bonding (MAHCB) was a new technology to prepare large-size homogeneous materials, the strain hardening at the bonding interface was an urgent issue for its application. In this paper, the effect of grain boundary migration on strain hardening was studied by the MAHCB process of pure copper. The results show that prolonging the holding time can significantly promote both interfacial grain boundary migration (IGBM) and matrix grain boundary migration (MGBM). The bonding interface became tortuous due to the promotion of IGBM, accompanied by the reduction in dislocation density at the interface and the gradual elimination of interfacial defects. It occurred mainly by the evolution of the triple junction grain boundary from T-type to equal type, which was driven by the decrease in the interface energy. On the other hand, the growth of dynamic recrystallization (DRX) grains was improved with MGBM, and enlarged the low dislocation density region. With the combined effect of both, strain hardening was completely eliminated, when the strain was 0.15 and the holding time was 3 h. Then the optimal bonding properties were obtained, the average tensile-shear strength and elongation were 191.2 MPa and 212 %, and the recovery rates were 99.7 % and 98.9 %, respectively, compared to the as-cast pure Cu samples.