Coarsening and age hardening behaviors of γ′ particles in GH742 during high temperature treatment

Abstract

The coarsening and ageing hardening behaviors of γ′ particles in superalloy GH742 have been investigated by field emission scanning electron microscopy (FESEM), coarsening kinetics calculation and microhardness testing when ageing at 1050, 950 and 900 °C for different time. The cube of γ′ particle size and ageing time follows a linear law as predicted by LSW theory. The particle size distributions give better fit to the LSW theoretical distribution. The activation energy for γ′ coarsening is accurately determined to have 245. 06±14. 42 kJ/mol when considering the effect of temperature on the solution concentrations in matrix. Based on the activation energy, the coarsening kinetics of γ′ particle is predicted as $\bar r_t^3 = 7.35 \times {10^{15}}\frac{{{C_e}}}{T}\exp \frac{{ - 245\,060 \pm 14\,420}}{{RT}}t$. The microhardness studies indicate that microhardness decreases rapidly with increasing the ageing temperature and it has a maximum value corresponding to a critical particle size beyond which the microhardness increase stalls with increasing the ageing time.