The effect of matrix microstructure and reinforcement shape on the creep deformation of near-γ titanium aluminide composites

The influences of composite matrix microstructure, reinforcement shape, and processing methodology have been evaluated for a series of near-gamma (Ti3Al+TiAl) titanium aluminide matrix composites evaluated in tension and tensile-creep at 800°C. Specifically, heat treatments were imposed to evolve either fully-equiaxed or fully-lamellar composite matrices containing either dispersed particulate or high-aspect-ratio short-fiber boride reinforcement. The results indicate that the highest creep rates are associated with composites containing particulate reinforcement in equiaxed matrices, whereas the lowest rates were obtained for short-fiber reinforcement in lamellar matrices. The mechanisms controlling creep deformation are observed to rely only on the morphology and details of the matrix microstructure and are independent of the type and shape of the reinforcing phase. The enhanced work hardening tendencies of the lamellar microstructure is shown to improve creep resistance as manifested by a reduced steady state creep rate as well as prolonging primary creep to higher values of accumulated strain.