MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF TI-40 WT PCT TA (TI-15 ATPCT TA)

Of the beta-isomorphous Ti-X alloy systems, Ti-Ta is one of the least studied. In the current work, the microstructure and mechanical proper ties of Ti-40 wt pct Ta (Ti-15 at. pct Ta) are investigated. Annealing at 810-degrees-C produces a two-phase microstructure consisting of Ti -rich alpha idiomorphs in a continuous Ta-rich beta matrix; this sugge sts the beta-transus temperature is higher than indicated by the most recently published phase diagram. Water quenching from 810-degrees-C c auses the beta phase to partially transform to orthorhombic martensite (alpha''), while furnace cooling yields secondary alpha. The primary alpha formed isothermally remains unchanged in both cases. Subsequent aging causes transformation of the martensite to type 1 alpha plus res idual beta with a corresponding increase in strength and decrease in d uctility. The maximum ductility (20 pct elongation) occurs in the wate r-quenched condition in which metastable beta is retained. Analysis of the true stress-true strain data suggests that transformation-induced plasticity may contribute to the enhanced ductility of the water-quen ched material.