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.% gamma' polycrystalline nickel-base superalloy have been studied using neutron diffraction at 20 degrees C, 400 degrees C, 500 degrees C, 650 degrees C and 750 degrees C with the results interpreted via (self-consistent) polycrystal deformation modelling. The data demonstrate that such experiments are suited to detecting changes of the gamma' slip mode from {111} to {100} with increasing temperature. Between room temperature and 500 degrees C there is load transfer from gamma' to gamma, indicating that gamma' is the softer phase. At higher temperatures, opposite load transfer is observed indicating that the gamma matrix is softer. At 400 degrees C and 500 degrees 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 gamma and gamma' 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 degrees C. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.