Structure studies of the R-phase using X-ray diffraction methods

The R-phase was induced in a binary polycrystalline 51.2 at.% Ni-48.8 at.% Ti alloy by deformation of epsilon = 5% followed by annealing at 350degreesC for 70h. This procedure allowed us to clearly separate the B2 --> R transformation from the R --> B19' one. In addition, a ternary Ni47Ti50Co3 alloy showed a gap of almost 40degreesC between these two transformations during cooling. The X-ray diffraction pattern of the R-phase was refined with the Rietveld method for three structure models with the following space groups: P3, P-3, and P31m, where the atomic positions were initially calculated from Patterson maps determined by the LeBail method. The best result was obtained for the model in P-3. (C) 2003 Elsevier B.V. All rights reserved.