Crystalline characteristics of alpha precipitates in Ti-15V-3Sn-3Al-3Cr alloy.

The experiment was designed to analyse the orientation relationship between alpha precipitates and beta matrix and to determine the habit plane of alpha phase in Ti-15-3 alloy using transmission electron microscopy. The orientation relationship was turned out to be 110(alpha)||111(beta) and (001)(alpha)||{110}(beta) obtained from diffraction patterns, which corresponded to Burgers orientation relationship. Based on the patterns and the crystal structure, it was determined that there were 12 possible orientation relationships between alpha precipitates with beta matrix and alpha precipitates had 12 variants. Meanwhile, the transformation matrixes of 12 orientation relationships were established. Diffraction patterns of 001(beta), 110(beta) and 311(beta) zone axes were also calibrated by these matrixes, which verified the correctness of proposed orientation relationship. Diffraction spots of lamelliform alpha precipitates spread along the [111](beta) and [1 1 1 ](beta) directions in diffraction patterns of [1 1 0](beta) zone axis, but they do not spread in diffraction patterns of [111](beta) zone axis, which indicates that the habit plane of variant 1, 2 and 3 is (111)(beta). Moreover, the habit planes of variant 4-6, variant 7-9 and variant 10-12 are (1 1 1)(beta), (1 1 1)(beta) and (1 1 1 )(beta) respectively. To sum up, the habit plane of alpha precipitates is {111}(beta).