Structure evolution in sputtered thin films of Ti_x(Ni, Cu)_1−x I: Diffusive transformations

Abstract

Diffusional transformations in Ti_x(Ni, Cu)_1−x thin films, with x = 0.474, 0.492 and 0.510 and containing about 5 at.% Cu, have been studied in materials fabricated by triode magnetron sputtering at 473 K. As-deposited films were amorphous and crystallized during isochronal annealing by a polymorphic reaction to form a precipitate-free fine-grained austenite phase that supported supersaturation either of Ti or of Ni + Cu at 300 K. Subsequent isothermal annealing generated precipitates which assumed specific crystallographic orientations with the parent lattice. Grain boundaries were subject to precipitation of Ti₄Ni₂O _x for both Ti-rich and Ni-rich compositions. (NiCu) ₂ Ti precipitates were found in tetragonal forms, and both Ti₄Ni₂O _x and Ni₃Ti₂ phases coexisted in the grain interiors in thin films of near-stoichiometric composition. Interface coherencies, misfit strain fields and special particle-matrix orientations were observed which have not been reported for alloys prepared by ingot metallurgy. As will be demonstrated in part II of this paper, these phenomena strongly influence thermoelastic martensite transformation behaviour.