Growth and dissolution behavior and morphology evolution of γ′ precipitates in GH4742 nickel-based superalloy

Abstract

This work systematically investigated the coarsening, dissolution, and morphological evolution behavior of γ′ precipitates in GH4742 superalloy through carefully designed heat treatment experiments. During long-term aging processes at 650 °C, 750 °C, and 850 °C, the coarsening model of γ′ precipitates followed the classic function of r3 vs. t, consistent with the classical Lifshitz-Slyozov-Wagner (LSW) coarsening model (diffusion-controlled). Due to higher diffusion coefficients of γ′ forming elements at higher temperatures, the coarsening rate K increased with aging temperature. The dynamical models for the dissolution of primary γ′ precipitates were established during sub-solvus (1080 °C) and super-solvus (1120 °C) heat treatment processes. The results indicated rapid dissolution of primary γ′ precipitates in the initial stages of solution heat treatment, with the dissolution rate gradually decreasing as the treatment time extended, approaching the γ′ precipitate size at thermodynamic equilibrium. During subsequent slow cooling at 14 °C/min after super-solvus (1120 °C) heat treatment, irregular-shaped γ′ precipitates formed through “aggregation” of adjacent γ′ precipitates, followed by “splitting” into smaller γ′ precipitates during growing up. Conversely, during subsequent slow cooling at 14 °C/min after sub-solvus (1080 °C) heat treatment, irregular-shaped γ′ precipitates were mainly controlled by unstable growth and “splitting” of cubic-shaped γ′ precipitates. For individual γ′ precipitates, the portion undergoing unstable growth (protrusions) did not undergo further splitting.

Keywords

• GH4742 superalloy
• γ′ precipitates
• Coarsening model
• Morphology evolution
• Sub-solvus heat treatment
• Super-solvus heat treatment