Phase transformations in sputtered thin films of Ti-x(Ni,Cu)(1-x) .2. Displacive transformations

Part I of this series described diffusional transformations in sputtered films of Ti-x(NiCu)(1-x) containing about 5 at.% Cu. The as-deposited amorphous films supported substantial supersaturation either of Ti or of Ni + Cu at 300 K. Subsequent isothermal annealing produced fine oriented precipitates which altered the matrix chemistry and often exerted long-range stress fields arising from coherency strains. These phenomena will be shown in part II to influence strongly the subsequent displacive transformation behaviour. In Ti47.4Ni46.5Cu6.1 films, precipitates of (NiCu)(2)Ti resulted in B2-->R and R-->B19' transformations. Extensive precipitation of Ti-2(Ni, Cu) in Ti51.0Ni44.4Cu4.6 films led to formation of an orthorhombic martensite, with preferred [010](B19)parallel to[011](B2) and (202)(B19)parallel to(2 (1) over bar 1)(B2) orientation relationships, prior to transformation to a monoclinic phase that formed along alternating {322}(B2) and {112}(B2) steps. Even in films with compositions near stoichiometry, small quantities of transgranular Ti40Ni56.5Cu3.5 and Ti-2(NiCu) precipitates significantly influenced transformation sequences, temperatures and details of martensite crystallography.