Ageing precipitation sequence and effect of. and secondary a 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 beta titanium alloy Ti-6Cr-5Mo-5V- 4Al during solution and ageing were investigated. Ageing from 400 to 450 degrees C, isothermal. phase (omega(iso)) precipitated in the alloy, resulting in high hardening and brittle fracture. After ageing at 450-500 degrees C,omega(iso) phase was gradually replaced by secondary alpha phase (a(s)) with the ageing time increasing. At higher ageing temperature (580-600 degrees C) omega(iso) precipitation was suppressed, and as phase precipitated directly from beta phase. The yield strength of sample aged at 450 degrees C for 12 h was 1368 MPa and the elongation was 5.5% due to omega(iso) precipitation. The yield strength of sample aged at 600 degrees C for 12 h was 1108 MPa and the elongation was improved to 15.4% due to the precipitation and coarsening of a(s) phase.