Effect of two phase warm rolling on aging behavior and mechanical properties of Ti–15Mo–5Zr–3Al alloy

Abstract

The isothermal aging behavior and change in tensile and mechanical properties of Ti–15Mo–5Zr–3Al alloy have been studied after three different pre-treatments, i.e. PR (rolling at partial solution temperature), PRP (PR+partial solution treatment) and C (complete solution treatment) by hardness and resistivity measurements, tensile and Charpy impact tests. After the PR and the PRP treatment, almost all of the plate-like primary α particles which were left in as-received specimens became granular, furthermore age-hardening was observed in that α+ β bi-phased specimens. Plate-like α is always formed by the aging. Sub-grain size of β phase in the PR and the PRP specimens is 1–2 μm, and no grain growth is observed during the aging. Tensile properties after 673 K-600 ks or 773 K-60 ks aging are improved by the PR or the PRP than the C pre-treatment. The fracture surface of the aged and tensile tested PR and PRP specimens shows dimples, whereas that of the C specimen shows flat surface, area fraction of 40–50%, due to grain boundary fracture. Deflection–load curve shows practically no change in its shape with variation in the pre-treatment, however maximum load is highest in the PRP specimen and decreases in order of the PR and the C. Total absorbed energy is also larger in the PR and the PRP specimens than in the C specimen in age-hardened state. The best strength–ductility balance is attained by the PRP specimen aged at 773 K for 60 ks.