Heating rate modulates γ' dissolution kinetics in powder metallurgy Ni-based superalloys: Dislocation-controlled diffusion pathway and quantitative modeling

The dissolution kinetics of γ' precipitates play a pivotal role in determining the microstructure of nickel-based superalloys during thermal treatment; however, the influence of heating rate on atomic diffusion mechanisms has remained inadequately understood. In this study, we employ a combination of experimental analysis and kinetic modeling to systematically examine γ' dissolution in a powder metallurgy Ni-based superalloy (FGH4113A) across heating rates ranging from 0.167 to 100 °C/s. We demonstrate that the heating rate governs the operative diffusion pathway: under rapid heating (5–100 °C/s), a high density of dislocations is preserved, facilitating pipe diffusion that markedly accelerates γ' dissolution, achieving full dissolution within 2–15 min. Conversely, slow heating (0.167 °C/s) leads to significant dislocation recovery, shifting the dominant mechanism to lattice diffusion and prolonging the dissolution process to 30–60 min. Notably, the heating rate also inverts the relative dissolution order of grain boundary (GB) and intragranular γ' precipitates: under slow heating, GB γ' dissolves preferentially due to enhanced lattice diffusion, whereas rapid heating promotes intragranular γ' dissolution via dislocation-mediated pipe diffusion—though in both regimes, smaller particles dissolve first. By coupling Johnson-Mehl-Avrami-Kolmogorov (JMAK) modeling with Arrhenius analysis, we develop a quantitative framework correlating heating rate and dislocation density with dissolution kinetics, as reflected in the effective diffusion coefficients (e.g., 19.58 × 10⁻³ μm²/s at 100 °C/s versus 4.86 × 10⁻³ μm²/s at 0.167 °C/s). These insights establish a mechanistic foundation for designing thermal processing routes to achieve optimized γ' microstructures in superalloys.