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 a radiation. The a and b 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 b. The phase composition of the specimen at selected times and temperatures was determined from spectra recorded in the range 32 -45°(2h), the scan time being~8 min. The technique was successfully used to monitor the kinetics of the a -b transition during heating and the b -a transition during cooling, including the transformation kinetics during isothermal holds. Measurements of the interplanar distance change with temperature for the crystallographic planes of a and b phases enabled derivation of the overall thermal expansion for the alloy using a rule of mixtures.

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