Yielding and work-hardening behavior of Ti–49at.%Al alloy in different test environment

Abstract

Tensile tests were carried out using a Ti–49at.%Al alloy in vacuum, air or flowing hydrogen gas at room temperature, 473 K and 573 K, before or after the specimens were exposed to a high temperature hydrogen gas. With increasing test temperature, in vacuum, the unexposed specimen tends to decrease the yield strength, elongation and work-hardening rate, whereas the exposed specimen exhibits the decrease in yield strength and an increase in elongation and work-hardening rate. The specimen tested in a flowing hydrogen gas at room temperature exhibits an increase in the yield strength and work-hardening rate, but drastically decreases the elongation, in comparison with those of the unexposed specimens tested in vacuum. The hydrogen, whether it exists inside or outside the specimen, results in a reduction in elongation from room temperature to 573 K. A small amount of hydrogen introduced during plastic deformation in a flowing hydrogen gas also affects their tensile properties. The higher yield strength and work-hardening rate in the exposed specimens is associated with the dislocation pinning.