Towards a better understanding of the phase transformations in explosively welded copper to titanium sheets

Abstract

The influence of post-process annealing on the growth kinetics of the intermetallic phases and mechanical properties of titanium/copper bimetallic sheets were analysed using scanning and transmission electron microscopies, X-ray synchrotron radiation, and mechanical testing. In order to weld two metal sheets, an explosive welding technique was utilised. Subsequently, the clads were subjected to post-weld annealing at 973 K from 0.25 to 1000 h. In the bonded state, the interface exhibited a wavy structure with only a small amount of solidified melt zones, composed of non-equilibrium phases of variable chemical compositions. After short annealing times (<1 h) these non-equilibrium phases transformed into equilibrium phases of TiCu4 and Ti3Cu4via spinodal decomposition. For longer annealing times (>1 h), the growth of four intermetallic layers: Ti2Cu, TiCu, Ti3Cu4, and TiCu4 situated along the entire interface is predominant. It was observed that the phases enriched with Cu and Ti were situated near the Cu and Ti parent sheets, respectively. The nano-hardness of the intermetallic phases decreased as the Ti content increased, whereas the Young's modulus reached its highest values for phases with equiatomic or close-to-equiatomic composition.