EVOLUTION OF A METASTABLE FCC SOLID-SOLUTION DURING SPUTTER-DEPOSITION OF TI-AL-B ALLOYS

The microstructure evolution of a nominally alpha-Ti-7Al-7B alloy synt hesized by sputter deposition has been examined. A highly supersaturat ed metastable single phase solid solution with a face centered cubic s tructure was identified as being the only phase present in the as-sput tered material. In contrast, Ti-7Al and Ti-7B alloys sputtered under t he same conditions were also single phase but exhibited the expected h exagonal structure of alpha-Ti. The selection of the fee phase is base d solely on kinetics, as the thermodynamically favored phase is always alpha (hcp). The reasons for the kinetic bias, however, are not clear . Annealing of the Ti-7Al-7B sputtered film at 900 OC for 1 h yielded precipitation of nano-scab TIE dispersoids in a single phase alpha-Ti matrix. Preliminary hardness and microstructural stability results of the dispersion unveiled promising potential for use of the physical va por deposition technique to deposit TiB strengthened Ti-matrices on fi bers in high-temperature metal matrix composites.