Tensile properties to 650° C and deformation structures in a precipitation-strengthened Ti-Al Alloy

Abstract

Appreciable strength levels were retained up to 650°C in a Ti-10 Al-1 Si alloy aged in the (α + α2) phase field to yield best room-temperature strength and ductility. The aging treatment precipitated such a uniform distribution of the α2 particles that at room temperature, dislocations bypassed instead of shearing the particles at low strains. Specimens fractured at room temperature exhibited fine uniform dimples even for those aging conditions that imparted no macroscopic ductility. A two-step aging process produced a higher volume fraction of bimodally distributed α2 particles that led to higher strength levels at elevated temperatures. Both for the single-size and the bimodal α2 particle distributions, elevated-temperature deformation structures consisted mainly of planar slip bands that sheared through the α2 particles.