AGE HARDENING EFFECT IN TI-6 AL-4V DUE TO OMEGA-PRECIPITATION AND ALPHA-PRECIPITATION IN THE BETA-GRAINS

The structure at room temperature of a quenched TA6V titanium alloy has been investigated. This structure is α +α′ or α +β according to the treatment temperature; it is always metastable. During ageing the β grains decomposed by the reaction β →β +ω +α →β +α; this decomposition was accompanied by a large increase of the 0.2% yield stress. No structural modification was observed in α. The α and β phase of TA6V were separately investigated in the form of single-phase alloys. The hardness of α was insensitive to ageing, while β was considerably hardened by ω and α; we deduced that the strengthening of the minor phase β during ageing is mainly responsible for the hardening of TA6V. © 1979 Chapman and Hall Ltd.