The formation of vacancy complexes through aging heat treatments between 800 and 1200K was studied for rapidly solidified NiAl and CoAl ribbons using TEM. In the case of the NiAl ribbons, the density of dislocations decreased with increasing annealing temperature, while voids with tens to a hundred nanometers in size were formed in a low density. In the CoAl ribbons, noteworthy microstructures of dislocations and voids appeared after annealing. A zone consisting of dislocation loops, in which prismatic loops 20–50nm in diameter had formed at high density, was found in the CoAl ribbons annealed at 800K for 360ks. On the other hand, voids with a size of several nanometers and a remarkably high density were formed by annealing not only at 800K but also at 1200K, suggesting that the growth rate of voids was extremely low because of low diffusivity in CoAl.

Supersaturated Vacancies and Vacancy Complexes in Rapidly Solidified B2 Aluminide Ribbons. R.Nakamura, K.Yoshimi, S.Tsurekawa: Materials Science and Engineering A, 2007, 449-451, 1036-40