Improving Creep Properties of IN718/316LN Transient Liquid Phase Bonding Joints by Controlling Evolution of Precipitate Phases

A long-term post-bonded homogenization treatment (PBHT) was designed to improve the creep properties of IN718/BNi-2/316LN transient liquid phase (TLP) bonding joints. Compared to conventional PBHT, creep life improved more than tenfold at 650°C and 150 MPa. Long-term PBHT inhibits cavities nucleation and growth by controlling precipitate evolution, effectively delaying creep rupture and reducing strain rate, as revealed by microstructural analysis and density functional theory (DFT). The segregation of Nb, Mo, and Si at the grain boundary, combined with the reduced nucleation energy barrier of Nb₃Si, facilitates its nucleation. Nb₃Si phase can modify the creep cavities shape factor, increase the cavities nucleation energy barrier, and reduce the cavities nucleation rate, thus delaying cavities formation. Additionally, high vacancy formation energy and interfacial adhesion work at the Nb₃Si/Ni interface further hinder the cavities nucleation. A kinetics model for creep cavities evolution is proposed based on the coordinative evolution between precipitates and cavities. This model can quantitatively describe the growth and coalescence of creep cavities and predict the creep rupture time accurately based on the dynamic evolution of intergranular precipitate phases. These findings provide insights into improving the creep properties of joints and heterogeneous materials, where creep cavities nucleate around precipitates.