Evidence of variation in slip mode in a polycrystalline nickel-base superalloy with change in temperature from neutron diffraction strain measurements

The deformation mechanisms under tensile loading in a 45 vol.% γ′ polycrystalline nickel-base superalloy have been studied using neutron diffraction at 20 °C, 400 °C, 500 °C, 650 °C and 750 °C with the results interpreted via (self-consistent) polycrystal deformation modelling. The data demonstrate that such experiments are suited to detecting changes of the γ′ slip mode from {1 1 1} to {1 0 0} with increasing temperature. Between room temperature and 500 °C there is load transfer from γ′ to γ, indicating that γ′ is the softer phase. At higher temperatures, opposite load transfer is observed indicating that the γ matrix is softer. At 400 °C and 500 °C, an instantaneous yielding increment of about 2% was observed, after an initial strain of 1.5%. This instantaneous straining coincided with zero lattice misfit between γ and γ′ in the axial direction. Predicted and experimental results of the elastic strain response of the two phases and different grain families showed good agreement at elevated temperatures, while only qualitative agreement was found at 20 °C.