Fracture behavior and mechanical properties of Ti-6Al-4V joints diffusion-bonded with pre-designed interfacial voids

This study focuses on the effects of interfacial voids on the mechanical properties and fracture behavior of the diffusion-bonded Ti-6Al-4 V joints. The joints with regular interfacial voids were designed and developed at 850 °C for 20 min. The initiation and propagation of cracks were illustrated through an in-situ tensile test, and the evolution of stress-strain field around interfacial voids was revealed via finite element models. The preferred propagation path of cracks was the edge of the earliest plastic zone where the coupled stress field was concentrated between adjacent interfacial voids. Spacing and size of interfacial voids significantly affected stress concentration around the voids, leading to premature nucleation of cracks at the tips of interfacial voids. The influence of spacing on strength and plasticity of the joint followed power laws. The joint strength reached 95 % of that of the base material when the spacing of interfacial voids was relatively 4 times length of interfacial voids, and the plastic deformation of the joint occurred. The joint fractured prematurely with a remarkable decrease of the plasticity when the length of interfacial voids was beyond 50 μm, and the joint strength decreased.