Evolution of a metastable FCC solid solution during sputter deposition of TiAlB alloys

The microstructure evolution of a nominally αTi7Al7B alloy synthesized by sputter deposition has been examined. A highly supersaturated metastable single phase solid solution with a face centered cubic structure was identified as being the only phase present in the as-sputtered material. In contrast, Ti7Al and Ti7B alloys sputtered under the same conditions were also single phase but exhibited the expected hexagonal structure of α-Ti. The selection of the fee phase is based solely on kinetics, as the thermodynamically favored phase is always α (hcp). The reasons for the kinetic bias, however, are not clear. Annealing of the Ti7Al7B sputtered film at 900 °C for 1 h yielded precipitation of nano-scale TiB dispersoids in a single phase α-Ti matrix. Preliminary hardness and microstructural stability results of the dispersion unveiled promising potential for use of the physical vapor deposition technique to deposit TiB strengthened Ti-matrices on fibers in high-temperature metal matrix composites.