Influence of intermetallic compounds on the microstructure and strength properties of diffusion bonded W-steel joints using Ti/Ni composite interlayer

Dissimilar W/steel metals were successfully joined by diffusion bonding process with the help of a Ti/Ni composite interlayer. The effect of bonding temperature and holding time on interfacial microstructure and mechanical properties of the bonded joints were investigated. Metallographic and compositional analyses show that no intermetallic compound was observed at the W/Ti and Ni/steel interfaces, but Ti2Ni, TiNi and TiNi3 were formed at the Ti/Ni interface at 850-1050 °C for 0.5-2 h. Tensile test showed that variations in the strength of the joint were strongly related to the intermetallic compounds in the diffusion zone of the Ti/Ni interface. The maximum tensile strength of ∼267 MPa was obtained for the joint diffusion bonded at 950 °C for 1 h, and the failure took place at both the W/Ti interface and W substrate. With further increase of the joining temperature, the holding time or both, the joint strength dropped as a function of the increase in the width of Ti-Ni intermetallic compounds, and the failure occurred at intermetallics layers of the Ti/Ni interface.