Residual thermal phase stresses in α-γ Fe-Cr-Ni alloys measured by a neutron diffraction time-of-flight method

Residual thermal phase elastic strains in rod specimens and powders with particle size from 150 to 250mum of alpha-gamma Fe-Cr-Ni alloys quenched from 1273 to 273 K, were measured by means of a high-resolution neutron powder diffractometer using a time-of-flight (TOF) method. Diffraction patterns were analyzed by the Rietveld method and the single-peak method. Residual thermal phase strains obtained in the rod specimens or the powders from the both methods are positive, i.e., tensile, for austenite (gamma) phase and negative for ferrite (alpha) phase, being consistent with the prediction from the difference in thermal expansion coefficients of the constituent phases. The Rietveld analysis combined with the TOF method is considered to give the most reliable results of the average thermal phase strain. The results by the single-peak analysis suggest that thermal phase strain shows [hkl] dependence; the absolute value of thermal phase strain is decreased with increasing of the Young modulus along the [hkl] direction.