Analysis of neutron diffraction spectra acquired in situ during mechanical loading of shape memory NiTiFe at low temperatures

The Spectrometer for Materials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory was used to acquire neutron diffraction spectra in situ during mechanical loading at 216 and 237 K. The experiments were performed with the objective of following the texture, strain and phase fraction evolution in the trigonal R-phase in a Ni46.8Ti50Fe3.2 shape memory alloy. A methodology to quantify the textures, strains and phase fractions using the General Structure Analysis System (GSAS) for Rietveld refinement of neutron diffraction spectra, is implemented and described. Emphasis is placed on evaluating the choice of P3 and P  3¯ space groups for the R-phase in the refinements and the impact of this choice on the quantitative analyses of spectra.