Role of matrix microstructure on: Room-temperature tensile properties and fiber-strength utilization of an orthorhombic Ti-alloy-based composite

Microstructure-property understanding obtained for a nominally Ti-25Al-17Nb (at; pet) monolithic sheet alloy was used to heat treat a unidirectional four-ply SCS-6/Ti-25Al-17Nb metal-matrix composite (MMC) and a fiberless ''neat'' material of the same alloy for enhancing mechanical properties. The unreinforced alloy and [0](4) composite recorded significant improvements' in ductility and strength, which were related to-the microstructural condition. Modeling of the tensile strength based on fiber fracture statistics helped in understanding how improved matrix microstructure provided more efficient utilization of fiber strength. In comparison to the [0](4) MMC, improvement of the [90](4) response was negligible, which was related to an alpha(2) stabilized zone around the fiber. A Nb coating on the fiber was used to modify the local microstructure, and it produced a modest improvement in strength and ductility in the transverse direction. Structure-property relations of the matrix under different heat-treatment conditions are described in terms of deformation and failure mechanisms of the constituent phases; alpha(2) (ordered hexagonal close-packed), B2 (ordered body-centered cubic), and O (ordered orthorhombic based on Ti2AlNb).