Adverse effects of continuous oxides at the diffusion bonding interface of RAFM steels and the improvement of joint strength by bonding pressure

Effects of bonding pressure on solid diffusion bonding of reduced activation ferritic/martensitic (RAFM) steel were investigated at a bonding temperature of 1050 degrees C for 60 min. Microstructure examination indicated that Cr-rich continuous oxides were formed at the bonding interface when the applied pressure was 10 MPa, deteriorating bonding quality of diffusion bonded joint. As the bonding pressure was increased to 20 MPa, uniform and consistent grains were formed at the bonding interface, exhibiting better diffusion bonding effect. The joints obtained under 10 MPa were characteristics of brittle fractures, and the fracture originated from the bonding interface. However, the joints obtained under 20 MPa failed at the base steel, and the fractures were characteristics of ductile fractures with dimples. Finite element analysis indicated that the increase in pressure could lead to the increase in strain at the bonding interface, which can effectively damage the continuous chromium oxide at the bonding interface, improving the bonding strength of the joints.