A creep constitutive model for Inconel 718-BNi2 brazed joints incorporating the dynamic interplay between dislocations and γ'' precipitate phases

Creep occurs inevitably in brazed joints, posing a significant challenge to the reliability of heat exchangers. To investigate the creep performance and failure mechanisms of Inconel 718-BNi2 brazed joints under intermediate-temperature and high-stress conditions, this study employs SEM, EBSD, and TEM for microstructural characterization. The results indicate that as the applied load decreases, the fracture mode changes from mixed fracture to brittle fracture, with a critical point near 570 MPa. The size of the γ’’ phase increases from 8.77 ± 3.07 nm to 20.63 ± 5.89 nm, indicating a decrease in the proportion of the shearing mechanism and an increase in the proportion of the Orowan mechanism in the interaction between dislocations and precipitated phases. Based on these findings, a constitutive model that accounts for the interaction between dislocations and precipitates is proposed. Based on the quantitative description of cumulative distribution function, the proposed model accurately describes the changes in the contributions of the shearing mechanism and Orowan mechanism to the evolution of dislocation density, and accurately exhibits the stress-creep strain relationship. Furthermore, the proposed model is validated by both finite element simulations and experimental results that it could accurately predict steady-state creep rates with a minimum error of 5.34 %. This model provides essential theoretical guidance for optimizing the brazing process and evaluating the service life of brazed joints.