Abstract
The nucleation of ω-related phases within B2-phase region in Ti-45Al-8.5Nb-(W, B, Y) (at.%) alloy were investigated by transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). At 850°C, the metastable B2 phase decomposes to ω particles quickly. Experimental evidence from high-resolution images revealed that first the atoms redistribute in the B2 structure, and then the original 11¯1B2 planes collapse during B2→ω″, which represents a “diffusion-collapse” pathway. The further collapse of (0001)ω planes in [0001]ω zone, that is ω″→ωo, is a sequential and uneven process rather than an instantaneous transition, which may be attributed to that an uneven structure transition could decrease the energy barrier.
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