Modeling the electrical response of waspaloy due to the nucleation, growth, and coarsening of γ'

Waspaloy is a polycrystalline nickel-base superalloy used in disc rotors for gas turbine engines. Waspaloy, like other superalloys, is strengthened through the formation of the γ' precipitate phase. As this precipitate phase evolves with processing and thermal exposure, it is desirable to non-destructively monitor the precipitate microstructural evolution. Electrical resistivity was used as such a non-destructive monitoring technique for aging temperatures ranging from 600°C to 800°C and aging times ranging between 2min and 263.5h. In the nucleation regime, a Johnson-Mehl-Avrami type equation was fit to the electrical response. For the growth and coarsening regimes, a volume distribution of precipitates was fit to the measured electrical resistivity. These fitting techniques were facilitated by microstructural data obtained from SEM imaging, X-ray diffraction, and small angle neutron scattering (SANS) measurements. For both cases, the models showed an excellent fit to the measured electrical data, implying that electrical resistivity is a viable technique for non-destructively monitoring the precipitate phase in Waspaloy.