Influence of Non-Equilibrium Structure on the Mechanical Properties of Heat-Resistant Titanium Alloy
The structure and fracture surface of a heat-resistant titanium alloy Ti-8,3Al-2,2Zr-2,1Mo-0,2Si-0,15Fe have been studied using scanning and transmission electron microscope. The room and high temperature tensile properties are obtained for all specimens. It is shown that short term exposure (10 min.) in b-region followed by air cooling results in the formation of a non-equilibrium solid solution while the treatment in b-region during 1 hour provides more equilibrium structure. Subsequent aging of the non-equilibrium structure at 500 ° C leads to the achieving of higher strength and plastic properties in comparison with properties of the alloy with initial equilibrium structure. Increasing the aging temperature to 700…750 ° C eliminates this difference. This effect is explained by different mechanisms of a→a2 transformation. In case of non-equilibrium state the formation of a2-phase occurs due to separate micro-volumes ordering by the homogeneous mechanism which provides increased strength and plastic properties. In case of the equilibrium state a2-phase formation occurs by the mechanism of nucleation and growth, which leads to ductility decreasing.