CRYSTALLOGRAPHIC ANALYSIS OF ALPHA-PHASE FORMATION IN A METASTABLE BETA-TI ALLOY

The beta/alpha '' duplex phase structure formed by quenching from beta phase region in a Ti-10V-2Fe-3Al alloy was aged at 673 and 873 K to p roduce alpha phase particles. Since the alpha phase particles exhibit the morphology similar to that of alpha' martensite, the processes of transformation have been analysed by the crystallographic theory of ma rtensite. At 673 K, very fine spherical omega phase particles precipit ate initially and then fine alpha platelets in specific directions rep lace with them as bands. At 873 K, on the other hand, coarse monolithi c alpha phase plates precipitate directly in the parent beta phase. Th e orientation relationships between alpha and beta phases in both case s are close to that of Burgers. The habit planes for both the alpha pl atelets and the alpha plates lie close to the (1 (2) over bar 2)(beta) and the (1 (1) over bar 1)(beta), respectively. The results can be ex plained consistently in terms of Bowles and Mackenzie theory by consid ering the condition that the elastic stress due to the shape change is relaxed by slips within the matrix.