Diffusion bonding of RAFM steels: Evolution of interfacial oxide layer with pressure and microstructure and mechanical property after post bonding heat treatment

The effect of increasing the bonding pressure from 10 to 20 MPa (5 MPa interval) at 1050°C for 60 minutes on the diffusion bonded joint of reduced activation ferritic/martensitic (RAFM) steel was investigated. The results indicate that the quality of the bond improves accordingly with increasing bonding pressure. The oxide layer at the bonding interface underwent an evolution process from continuous to discontinuous and ultimately disappeared with the increase of bonding pressure. The optimal joint was achieved in this work at the pressure of 20 MPa. Considering the research of reliability of joints in engineering applications, the optimum joint was subjected to post-bonding heat treatment (PBHT) of 750°C for 90 minutes. The diffusion bonded sample subjected to PBHT exibits microstructural features and tensile properties similar to those of the base metal. It is noteworthy that the tensile fracture does not occur at the bonding interface, but in the base metal far away from the interface. This work can provide a feasible method for the removal of oxides at the diffusion bonding interface of RAFM steel and also contribute to the establishment and optimization of diffusion bonding processes, thereby improving the quality of the diffusion bonding joint.