Influence of interfacial defects on the impact toughness of solid state diffusion bonded Ti–6 Al–4 V alloy based multilayer composites

Microstructure and mechanical properties, with emphasis in impact toughness behaviour, of two multilayer composites have been investigated. The multilayer materials are constituted by thirteen layers of high strength Ti–6 Al–4 V alloy. Stacked layers have been successfully joined by diffusion bonding considering two processing temperatures, 750 and 900 °C. The proportion of α/β phase in the microstructure during diffusion bonding process determines the presence of pores at the interface, and therefore the mechanical properties of the composite material. Higher bcc β phase proportion during diffusion bonding process at the highest temperature of 900 °C leads to high bonding degree, without noticeable toughness increase of the multilayer composite. In contrast, higher proportion of harder hcp α phase at 750 °C makes difficult the healing of interfacial pores, decreasing interfacial toughness and leading to a toughness value of the multilayer composite seven times higher than the reported value for the as-received Ti–6 Al–4 V alloy.