Orientation and morphology variants of the α2 phase in B2 parent matrix in a super α2 titanium aluminide alloy

Abstract

Titanium aluminides are potential low density, high stiffness, high-temperature materials that use ordered crystal lattices to retain strength at elevated temperatures. The super α2 system is based on the hexagonal DO19 α2 phase (Ti3Al), but has sufficient β (BCC, high temperature phase) stabilizing elements (Nb, V and Mo) so that a continuous B2 ordered cubic phase is retained to room temperature. Transmission electron microscopy (TEM) images and selected area electron diffraction (SAD) patterns were used to analyze the crystallography and morphology of the α2 phase that forms when 100% B2 phase is aged at 1000°C for one hour. TEM is the only technique that provides both precise crystallographic and morphological analysis of the phase transformation.The microstructure produced from 100% B2 material, formed by ice brine quenching the super-α2 alloy from 1250°C, by aging at 1000°C for 1 hr is shown in the scanning electron micrograph in Figure 1. The dark discontinuous phase is acicular α2, while the light continuous phase is the ordered cubic B2 phase.