In this study, the influence of aluminum content on shape memory effect of Ti–7Cr–Al alloys fabricated using low-grade sponge titanium was investigated by measurement of electrical resistivity and Vickers hardness, along with shape-recovery testing. The results obtained are as follows.
In the STQed state, the phase constitution of non-Al added alloy, Ti–7Cr–0Al alloy, was found to consist of retained β phase and athermal ω, whereas those of Al added alloys, Ti–7Cr–1.5Al, 3.0Al and 4.5Al alloys, were found to consist of orthorhombic martensite, α″, and retained β phase. Resistivity (ρ) at liquid nitrogen (LN) and room temperature (RT) increased monotonously with Al content. Resistivity ratio (ρ_LN⁄ρ_RT) increased drastically at 3Al, exceeding unity.
Shape recovery was exhibited in the 1.5Al, 3.0Al, and 4.5Al alloys having been fabricated using low-grade sponge titanium as raw material. In the 3.0Al and 4.5Al alloys, shape recovery ratio was about 90% at temperatures above 523 K and recovery surface strain was at least 0.03. The resistivity change indicates that stress-induced orthorhombic martensite was produced during bending of the 4.5Al alloy.