High cycle fatigue and fatigue crack propagation behaviors of β-annealed Ti-6Al-4V alloy

Abstract

Background: 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. Methods: The tensile tests, stress-controlled HCF tests, and FCP tests were conducted, and the fractographic and micrographic analyses were performed before and after the tests. Results: The 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. Conclusions: Relatively 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.

Impact of Cryogenic Treatment on HCF and FCP Performance of β-Solution Treated Ti-6Al-4V ELI Biomaterial

“…It is clear from straight line slipping shown in Figure 7a. The results are in complete agreement with earlier research studies [41,44]. The crack path followed by B2 specimen is quite tortuous due to deflections caused by prior β grain boundaries and orthogonal needle like martensite α'.…”

“…The random orientation of martensite α' within prior β grain also leads to the generation of secondary cracks reflected in terms of river like slipping as shown in Figure 7b. Bifurcations of macrocracks into secondary microcracks and severe deflections of cracks in β heat treated Ti-6Al-4V has also been reported by earlier research studies [41,43,44]. The net effect of crack deflection is to disperse the strain field energy of the macroscopic crack into multiple secondary microcracks resulting in a significant reduction in fatigue crack growth [44].…”

“…The improvement in the HCF property, reflected in terms of the increased number of cycles to failure, had happened due to a combined effect of a decrease in the size of prior β grain, formation of massive α patch and its subsequent transformation into ultra-fine α and β during the soaking period at −196 °C. Improvement in HCF performance with a reduction in the size of the prior β grain has also been reported earlier in different research studies [41][42][43]. Fractography using scanning electron microscopy was done to have further insight into the nature of failure and analysis of fractured surface.…”

An overview of factors affecting high‐cycle fatigue of additive manufacturing metals

“…​​ 22 Due to the porosity of the Ti64 material produced by AM, it is observed in literature studies that the fatigue life of Ti64 decreases in HCF and very high‐cycle fatigue (VHCF) behavior 23–26 . The decrease in the fatigue strength values of Ti‐6Al‐4V alloys produced by AM is expressed by different factors affecting their fatigue life in low‐cycle fatigue (LCF) and HCF performance 27 . While crack propagation and material plasticity are the factors affecting fatigue life in LCF behavior, crack initiation plays a more active role in HCF behavior 28 .…”