Effect of Aging Treatment on the Microstructure and Resistivity of a Nickel-Base Superalloy

The γ′ precipitation behavior of age-hardened WASPALOY, aged at 998 K, 1073 K, and 1148 K (725 °C, 800 °C, and 875 °C) for times ranging from 0.5 to 263.5 hours, were evaluated via analysis of ultra small angle X-ray scattering (USAXS) curves and scanning electron microscopy (SEM) micrographs. The USAXS spectra revealed a single precipitate size distribution at the earliest aging times, which evolves into a bimodal precipitate size distribution at later aging times. The primary precipitate radius displayed t 1/3 coarsening dependence for aging at 1073 K and 1148 K (800 °C and 875 °C); however, the primary radius increased with t 0.4 dependence at 998 K (725 °C), most likely due to mixed growth and coarsening. A figure of merit, η ′, consisting of two terms, one associated with precipitate size and volume fraction and the other with compositional fluctuations, was proposed. η ′ shows direct empirical correlations with changes in the measured electrical resistivity.