Influence of Short-Time Duplex Heat Treatment on Fatigue Strength of Ti-6A1-4V Alloy
Tatsuro MORITA, Kosuke SHINODA, Kazuhiro KAWASAKI and Yositaka MISAKA
Abstract:Influence of short-time duplex heat treatment on the fatigue strength of + titanium alloy Ti-6Al-4V was investigated. When the alloy was solution-treated for 60 s at 1203 K and water-quenched, prior phase was hardened since a part of this phase was transformed to acicular martensite phase. With subsequent aging for 40 s at 753~903 K, fine phase was precipitated in retained phase so that hardness of prior phase further increased. Such hardening of prior phase remarkably improved the fatigue strength of the alloy as well as its yield stress and tensile strength. That was because slip in primary phase, where would be fatigue crack initiation sites, was restricted by hardened prior 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 phase. Key Words:Titanium alloy, Ti-6Al-4V, Short-time duplex heat treatment, Microstructure, Martensite, Retained phase, Hardness, Mechanical properties, Fatigue strength