Effect of isothermal aging on phase constitution and mechanical properties of Ti–Cr alloys

In this study, the effect of isothermal aging on phase constitution and mechanical properties of Ti–Cr alloys was investigated by measurements of electrical resistivity and Vickers hardness, X-ray diffraction, optical and scanning electron microscope observations and tensile tests. The obtained results are as follows. In solution treated and quenched state (STQ), hexagonal martensite, α′ was identified at 3Cr and 5Cr alloys, whereas β phase was identified from 5Cr to 20Cr. In 7Cr and 10Cr, athermal ω was also identified. Maximum of HV appeared at 7Cr and then HV decreased with increase of Cr content up to 15Cr. Above 15Cr, HV slightly increased due to solution hardening by Cr addition. On isothermal aging, precipitation of the α phase was delayed by Cr addition. In STQed state, tensile strength is 961 MPa in 10Cr, 988 MPa in 13Cr and 967 MPa in 15Cr, respectively. Elongation is 27.1% in 10Cr, 26.8% in 13Cr and 23.9% in 15Cr, respectively. In 13Cr and 15Cr alloys, nominal stress-nominal strain curves showed work-softening phenomenon after yield stress, whereas S–S curve of 10Cr alloy did not show that phenomenon. In 1173 K−12 ks aged state, tensile specimens of 10Cr and 13Cr were broken with no elongation, while the specimen of 15Cr alloy was broken after about 5% in elongation. It is considered that the reason why aged 10Cr and 13Cr specimen show no elongation is due to precipitation of α.