(011)<sub>γ</sub>/(101)<sub>γ</sub> order twin of γ lamella in a Ti-40 at.% Al alloy
Yang, Y. S.; Wu, S. K.; Yang, Y. S.; Institute of Materials Science and Engineering, National Taiwan University; Wu, S. K.; Institute of Materials Science and Engineering, National Taiwan University
Журнал:
Philosophical Magazine A
Дата:
1992
Аннотация:
AbstractTransmission electron microscopic study on a α<sub>2</sub> + γ two-phases Ti-40 at.% Al alloy demonstrates that (011)<sub>γ</sub>/(101)<sub>γ</sub> twin does occur in TiAl. Differently-orientated γ regions are observed to coexist within the same γ lamella with the (011)<sub>γ</sub>/(101)<sub>γ</sub> twin plane as their boundary. The variants pair corresponding to these differently-orientated γ regions should come from variants which have the same stacking sequence. The mechanism for the formation of (011)<sub>γ</sub>/(101)<sub>γ</sub> twin plane is suggested to grow from the ‘APB-induced fault’ formed in the γ lamella during the precipitation transformation of α<sub>2</sub>→α<sub>2</sub> + γ. Total strain induced by the structure change (h.c.p.→f.c.c.) and by the tetragonality of γ phase during the precipitation transformation can be minimized by a composite of {111}<sub>γ</sub> and {011}<sub>γ</sub> twins coexisting in γ lamellae.
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