Using Variant Selection to Facilitate Accurate Fitting of γ Peaks in Neutron Diffraction

gamma '' diffraction peaks are hard to discern in neutron/X-ray diffraction patterns, hindering studies on the gamma ''-strengthened superalloys using in-situ diffraction. In this study, we propose a variant selection method to increase the intensity of gamma '' peaks and to facilitate accurate fitting. The specific variants of gamma '' are controlled by applying a 300 MPa tensile stress during aging at 790 degrees C for 5 hours. The interaction energy between the applied stress and the transformation strain of each gamma '' variant differs, leading to an increase in the amount of the variants with a greater energy reduction at the expense of other variants. The enhanced variants result in greater gamma '' peak intensities in neutron diffraction patterns, allowing both the Pawley refinement and single peak fitting to be performed. Lattice parameters of gamma '' and gamma phases, and lattice misfit between the two phases and volume fraction of gamma '' are acquired. The uncertainties associated with the fitting maintain an acceptable level corresponding to 150 microstrains. The proposed variant selection method shows potential for studying the role of gamma '' phase in Ni-base superalloys. (C) The Author(s) 2019