Microstructures of crystallized Ti51.5Ni48.5−xCux (x = 23.4–37.3) thin films

The microstructures of Ti51.4Ni25.2Cu23.4, Ti51.3Ni21.1Cu27.6, Ti51.2Ni15.7Cu33.1, and Ti51.4Ni11.3Cu37.3 thin films annealed at 773, 873 and 973 K for 1 h were investigated. The Ti51.2Ni15.7Cu33.1 and Ti51.4Ni11.3Cu37.3 films showed very small grain sizes (120 and 50 nm, respectively) compared with the Ti51.4Ni25.2Cu23.4 and Ti51.3Ni21.1Cu27.6 films (1 and 0.3 μm, respectively). They had no precipitates within the B2 grains. On the other hand, the Ti51.4Ni25.2Cu23.4 films annealed at 773 and 873 K showed GP zones and Ti2Cu precipitates, respectively, and the Ti51.3Ni21.1Cu27.6 film annealed at 773 K showed TiCu precipitates in the grain interiors. The formation of precipitates in the grain interior was discussed in terms of the lattice mismatch between the precipitates and the matrix. The difference in grain size was attributed to different crystallization processes.