Use of high temperature X-ray diffractometry to study phase transitions and thermal expansion properties in Ti-6AI-4V

Phase transitions in Ti-6Al-4V were studied by means of high temperature X-ray diffraction using a resistance heated furnace in high vacuum and Cu K-alpha radiation. The alpha and beta phases could be observed conveniently using the (10.0), (00.2) and (10.1) peaks of the a structure and the (110) peak of the beta. The phase composition of the specimen at selected times and temperatures was determined from spectra recorded in the range 32-45degrees (2theta), the scan time being similar to 8 min. The technique was successfully used to monitor the kinetics of the alpha - beta transition during heating and the beta-alpha transition during cooling, including the transformation kinetics during isothermal holds. Measurements of the interplanar distance change with temperature for the crystallographic planes of alpha and beta phases enabled derivation of the overall thermal expansion for the alloy using a rule of mixtures.