The lattice misfit at the interfaces between these B2- and L21-structured components of the pseudo-binary NiAl-NiTi system was estimated by means of transmission electron microscopy. It was found that, when the Ni2AlTi precipitates were smaller than a critical size, the precipitates maintained their coherency with the NiAl and NiTi matrices. After longer periods of aging, the Ni2AlTi precipitates lost their coherency due to the introduction of interface dislocations around them. This coherency loss occurred catastrophically, and the shape of the precipitates changed to a globular one after the coherency loss, while the cubic-cubic orientation relationship was retained. Contrast experiments revealed that the Burgers vectors of these misfit dislocations were of a<100> type, with the pure edge component lying on the surface of the Ni2AlTi phase. The degree of lattice misfit at NiAl/Ni2AlTi and Ni2AlTi/NiTi interfaces was estimated from the spacings of the misfit dislocations. It increased, with decreasing aging temperature, in both systems.

K.Ohishi, Z.Horita, M.Nemoto: Materials Transactions, 1997, 38[2], 99-106