Small angle neutron scattering (SANS) study of γ' precipitates in single crystals of AM1 superalloy

The morphology of γ' precipitates of AM1 single crystal superalloys has been studied by small neutron scattering (SANS), and electron microscopy. Due to the single crystal nature of the samples, the SANS patterns are anisotropic and exhibit a fourfold symmetry corresponding both to the shape and to the spatial arrangement of the precipitates in a (001) plane. Measurements for other sample orientations have allowed us to improve the analysis of the shape of the precipitates. After creep deformation along the < 001 > axis, a twofold symmetry corresponding to the “rafting” of the γ' precipitates is observed in the (010) plane. The main effect of heat treatments at 1 050 °C, commonly used for industrial applications, is the coarsening of the precipitates. From the displacement of the correlation peaks towards smaller angles, we deduce an average centre-to-centre spacing between the precipitates which increases with the annealing time from 0.3 μm to 0.6 μm according to the Lifshitz, Slyosov, Wagner behaviour. The results are compared to electron microscopy measurements, performed on the same samples.