Microstructure and fretting fatigue characteristics of a Ti-4.5%Al-3% V-2%Mo-2%Fe alloy.

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Abstract
Recently, Ti–4.5Al–3V–2Mo–2Fe, which is an alpha + beta type titanium alloy with excellent superplastic characteristics, has been developed for structural applications. In the case of using as aircraft materials, the fretting fatigue fracture, which is caused by the combination of cyclic fatigue stress and fretting, is highly expected. Microstructure of Ti–4.5Fe–3V–2Mo–2Fe is variously changed by heat treatments. Therefore, the effects of microstructures on fretting fatigue characteristics of the alloy conducted with various annealing treatments in alpha + beta field were investigated in this study. The fretting fatigue strength seems to be independent of microstructure in low cycle fretting fatigue life region. While, the fretting fatigue limit of the alloy tends to increase with decreasing area fraction and average diameter of primary alpha phase. However, when area fraction and average diameter of primary alpha phase are below certain values, the fretting fatigue limit is lowered by coarsening of acicular alpha phase, which precipitates in beta phase region.