Abstract
BackgroundThe effect of β annealing on high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors of Ti64 alloy were examined, and the results were compared to those of mill-annealed counterpart.MethodsThe tensile tests, stress-controlled HCF tests, and FCP tests were conducted, and the fractographic and micrographic analyses were performed before and after the tests.ResultsThe β-annealed Ti64 specimen showed inferior HCF properties as compared to the mill-annealed counterpart, as a result of lower yield strength. On the other hand the resistance to FCP of β-annealed Ti64 specimen was higher than that of mill-annealed counterpart in low and intermediate ΔK regime.ConclusionsRelatively easy fatigue crack initiation at the colony boundaries of β-annealed Ti64 specimen reduce the resistance to HCF. The resistance to FCP of β-annealed Ti64 specimen increased significantly particularly in low ΔK regime along with severe crack branching and deflection.
Highlights
The effect of β annealing on high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors of Ti-6Al-4 V (Ti64) alloy were examined, and the results were compared to those of mill-annealed counterpart
A number of literatures have demonstrated that different heat treatment routes can produce a variety of microstructures in α + β Ti-6Al-4 V (Ti64) alloys, which strongly affects the static and dynamic properties (Venkatesh et al 2009; Morita et al 2005; Semiatin et al 2003; Ivasishin et al 2002; Chandler 1996)
In α + β titanium alloys, thermal instability is a function of β phase transformation since, cooling from the annealing temperature, the β phase can transform to the undesirable intermediate ω phase (Donachie 2000; Froes 2015; Rajan et al 2011)
Summary
The effect of β annealing on high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors of Ti64 alloy were examined, and the results were compared to those of mill-annealed counterpart. The use of titanium alloys in airframe application has recently been growing as the use of CFRP (carbon fiber reinforced polymer) increases (Inagaki et al 2014; Mrazova 2013) It is because designing joints between heterogeneous materials in an airframe must consider the prevention of galvanic corrosion and the elimination of strain caused by the difference in thermal expansion coefficients (Kaminaka et al 2014; Donachie 2000). To prevent the formation of ω phase, a stabilization anneal is generally given for the α + β titanium alloys (Donachie 2000; Froes 2015) This annealing treatment produces a stable β phase capable of resisting further transformation when exposed to elevated temperatures in service. The α + β Ti64 alloy that is lean in β can be air cooled from the annealing temperature without impairing their stability (Donachie 2000; Campbell 2008)
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