Creep deformation and interfacial fracture mechanisms of diffusion-bonded PM Ni-based superalloy

An advanced PM superalloy was diffusion-bonded using electroplated nickel as an interlayer, followed by HIP and a two-step heat treatment. The creep properties of the bonded specimens were systematically investigated under three typical temperature/stress conditions, namely 650 °C/790 , 750 °C/480, and 704 °C/690 MPa. Among the three tested temperature/stress combinations, the bonded interface exhibited the lowest creep resistance under the 704 °C/690 MPa condition, characterized by the shortest creep life (402 h) and the largest creep strain at equivalent testing times. Fractographic analysis by SEM and EBSD revealed that a larger source zone area on the fracture surface was the primary factor contributing to the longer creep life under the 750 °C/480 MPa condition. TEM observations across three distinct interfacial regions revealed different deformation mechanisms: isolated superlattice stacking faults in the matrix region, multiple-orientation microtwins in the transition region, and dislocation piling-up around coarse γ′ precipitates in the interfacial precipitated phase region. The continuous accumulation of dislocations around coarse γ′ precipitates generated significant stress concentration at the interface, which eventually exceeded the interfacial bonding strength and led to interfacial debonding and final fracture. This study provides a comprehensive understanding of the creep behaviour and failure mechanisms of diffusion-bonded powder metallurgy superalloy joints.