Ageing precipitation sequence and effect of ω and secondary α phases on tensile properties of metastable β Ti-6Cr-5Mo-5V-4Al alloy

The ageing precipitation sequence and the relationship between microstructure and tensile properties of metastable β titanium alloy Ti-6Cr-5Mo-5V-4Al during solution and ageing were investigated. Ageing from 400 to 450 °C, isothermal ω phase (ωiso) precipitated in the alloy, resulting in high hardening and brittle fracture. After ageing at 450–500 °C, ωiso phase was gradually replaced by secondary α phase (αs) with the ageing time increasing. At higher ageing temperature (580–600 °C), ωiso precipitation was suppressed, and αs phase precipitated directly from β phase. The yield strength of sample aged at 450 °C for 12 h was 1368 MPa and the elongation was 5.5% due to ωiso precipitation. The yield strength of sample aged at 600 °C for 12 h was 1108 MPa and the elongation was improved to 15.4% due to the precipitation and coarsening of αs phase.