X-RAY-POWDER DIFFRACTION STUDY OF THE R-PHASE IN A TI50NI48FE2 ALLOY BY A NEW CALIBRATION METHOD

the R-phase in a polycrystalline 50Ti48Ni2Fe shape memory alloy has be en here investigated by X-Ray Powder counter Diffractometry (XRPD). Wi th the aim to determine the R-phase lattice parameters accurately, an original XRPD calibration method, specifically apt for shape memory al loys, has been developed. The intrinsic aberrations that affect the XR PD have been taken into account by evaluating the XRPD spectrum of the high temperature b.c.c. phase. The correction function Delta(2 theta) has been calculated and applied to the R-phase diffraction peaks. A f ull indexing of the X-ray spectrum of the R-phase, not achievable by r aw experimental data, has thus been obtained and the lattice parameter s calculated on a set of reflections in un-aberrated angular positions with an accuracy of approximate to 1 part in 10000. The calibration m ethod here developed can be used also in the XRPD study of crystalline materials that undergo a first solid-solid phase transition.