Microstructure and mechanical properties of TLP diffusion bonded joint of MGH956/GH3230 superalloy

Transient liquid phase (TLP) diffusion bonding of MGH956 to GH3230 superalloy was conducted using BNi5 amorphous foil as the interlayer. The effect of bonding temperature and holding time on the interfacial microstructure and mechanical properties of the bonded joints was investigated at room and high temperature, respectively. The resultant MGH956/BNi5/GH3230 TLP joints fabricated at 1200 °C/2 h consisted of diffusion affected zone α (DAZ α), isothermal solidification zone (ISZ) and diffusion affected zone γ (DAZ γ). In DAZ α, no second phase was formed in the diffusion affected zone, but some oxide particles accumulated at the MGH956/BNi5 interface. In DAZ γ, massive Cr–W borides formed at the grain boundaries while granular and needle borides precipitated in the grain of diffusion affected zone. The microstructure evolution of the weld seam during TLP diffusion bonding was deduced as: L → γ-Ni + L → γ-Ni + (Cr, Fe)B + (Cr, W)B → γ-Ni + (Cr, W)B → γ-Ni + (Ni, Fe)Al. With the increase of holding time, the tensile strength of the bonded joint at 950 °C decreased first and then increased, which was opposite to the tensile strength at room temperature. The tensile strength at room temperature reached 715 MPa when the joint was bonded at 1170 °C for 1 h. The joints failed at the MGH956 base material with a ductile fracture mode. Meanwhile, the tensile strength of the resultant joint tested at 950 °C reached 89 MPa. The results of the fracture analysis suggested that oxide particles aggregated at the interface of MGH956/BNi5 exhibited low resistance to crack at 950 °C, resulting in failure with brittle intergranular fracture characteristics. • Successful TLP diffusion bonding of MGH956 to GH3230 with BNi5 interlayer was conducted. • The effect of bonding parameters on the tensile strength of joints at room and high temperatures was considered. • The connection between the microstructure and mechanical properties of bonded joint at room and high temperature was established. • Reasonable control of holding time can avoid Cr–W boride coarsening and obtain joints with room temperature tensile strength equal to the base material.