The fatigue and fracture properties of titanium alloy rods play an important role in determining the service life of the alloy. It has been studied at home and abroad for many years to explore the fatigue and fracture mechanisms of titanium alloy rods and their relationship with various metallurgical factors. Due to the complexity of the problem itself and the dispersion of preliminary test data, some substantive issues are still unclear, and views are not fully unified. Only some representative conclusions are introduced here.
The fatigue life of grade 5 titanium alloy rods, like other materials, depends on the probability of fatigue crack nucleation and the growth rate of cracks. According to the research on pure titanium, fatigue cracks are mostly nucleated in the slip zone and at the twin interface, but for Ti-6AI-4V alloys, the interface between a phase and b phase is relatively weak under low stress conditions. Only at high stress levels, the probability of nucleation in the slip zone increases significantly, and increasing the test temperature has a similar effect. In order to improve the fatigue performance, it is usually desirable to obtain a small equiaxed a-b type titanium alloy rod. b organization, and the b phase is preferably in a free state, so as to reduce the a/b phase interface area. In addition, the fine-grain slip is relatively uniform, and the free path of slip is short, which can reduce the stress concentration caused by the accumulation of dislocations. On the other hand, the coarse-grained Widmandarin microstructure has low fatigue strength due to the easy nucleation of fatigue cracks. Effect of grain size on fatigue properties of smooth and notched specimens of Ti-6A1-4V alloy.
In the presence of notches and stress concentration, the effect of grain size is reduced, because the fatigue life mainly depends on the crack growth rate at this time, and the experimental results of pure titanium show that the crack growth rate is not closely related to the grain size.
Nicole
Company: Baoji Jimiyun Dynamic Co., Ltd
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