Coarsening kinetics of γ′ precipitates in a Re-containing Ni-based single crystal superalloy during long-term aging

The morphological evolution and coarsening kinetics of gamma' precipitates in a Re-containing Ni-based single crystal superalloy were investigated during isothermal aging at 900, 950 and 1000 degrees C. After heat treatment, well-defined cuboidal gamma' precipitates with low misfit was obtained within the experimental alloy. Then coarsening rate constants and particle size distribution (PSD) of gamma' phases were calculated and specified based on the measured precipitate sizes for varying periods of aging times from 100 to 2000 h. After aging for 2000 h, gamma' precipitates maintained cubical shape at 900 degrees C, while exhibited sphere at 950 and 1000 degrees C. Coarsening models based on diffusion-controlled process with a functional relationship of r(3) vs. t (classic Lifshitz-Slyozov-Wagner coarsening model) and interface-controlled model with a function of r(2) vs. t (trans-interface diffusion-controlled coarsening model) were investigated to fit between the experimental results and theoretical analysis. It was found that Re as the slowest diffusing solute in the alloy constituted the rate-limited step for coarsening based on LSW model, while the process limiting coarsening as governed by an interface diffusion process could possibly be related to the Al diffusion through the gamma/gamma' interface. The PSDs and coarsening exponent were discussed by comparing the experimental data with predictions of LSW and TIDC models. Finally, coarsening mechanism could be divided into four regimes: (i) coarsening by diffusion-controlled; (ii) coarsening by diffusion and interface co-controlled; (iii) coarsening by interface-controlled; (iv) coarsening by interface-controlled accompanied with gamma' coalescence. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

The morphological evolution and coarsening kinetics of gamma' precipitates in a Re-containing Ni-based single crystal superalloy were investigated during isothermal aging at different temperatures. Different coarsening models were examined to fit between the experimental results and theoretical analysis, revealing the role of Re and Al diffusion in the rate-limiting steps of coarsening. The coarsening mechanism was divided into four regimes based on the experimental data and predictions of models.