Influence of short-time duplex heat treatment on fatigue strength of Ti-6Al-4V alloy

Abstract

Influence of short-time duplex heat treatment on the fatigue strength of α + β titanium alloy Ti-6Al-4V was investigated. When the alloy was solution-treated for 60 s at 1203 K and water-quenched, prior β phase was hardened since a part of this phase was transformed to acicular α' martensite phase. With subsequent aging for 40s at 753-903 K, fine a phase was precipitated in retained β phase so that hardness of prior β phase further increased. Such hardening of prior β phase remarkably improved the fatigue strength of the alloy as well as its yield stress and tensile strength. That was because slip in primary α phase, where would be fatigue crack initiation sites, was restricted by hardened prior β phase so that fatigue crack initiation was suppressed to high stress amplitude level. In the examined treatment conditions, the combination of the above short-time solution treatment and aging for 40 s at 803 K was suitable to improve the strengths. In this case, the tensile strength and fatigue strength were increased by 29 % and 22%, respectively. At the same time, ductility was also increased by 10 % due to stress-induced martensitic transformation of retained β phase. © 2007 The Society of Materials Science.