In situ neutron diffraction on the alloy 50.6Ti-36.5Al-12.9Nb (at.%)

The phase transformations occurring during heating/cooling in the 50.6Ti-36 .5Al-12.9Nb (at.%) alloy have been studied by using in situ neutron diffrac tion between 25 and 960 degrees C, which allows the observation of the supe rlattice reflections of the B2 phase, ordered form of the b.c.c. beta phase , on the contrary to X-ray diffraction. The equilibrium state of this alloy is three-phased: alpha(2) + gamma + omega at low temperatures and B2 + alp ha(2) + gamma at high temperatures. The B2, alpha 2 and gamma phases are or dered at least up to 960 degrees C. During the cooling the B2 --> omega tra nsformation takes place around 800 degrees C. The volume fractions of the p hases existing at different temperatures have been calculated from spectra treated by the profile refinement method of Rietveld. The results have been found in satisfactory agreement with our previous results determined by im aging analysis and thermodynamical calculation.