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Factors Affecting The Service Time Of Titanium Alloy Rod
Date：
2021-11-12 11:03
The fatigue and fracture properties of titanium alloy rods play a very important role in determining the useful life of the alloy. Over the years, it has been studied at home and abroad to explore the fatigue and fracture mechanisms of titanium alloy rods, as well as 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 opinions are not fully unified. Here we only present some representative findings.
The fatigue life of titanium alloy rods, like other materials, depends on the probability of fatigue crack nucleation and the rate of crack growth. According to research on pure titanium, fatigue cracks nucleate mainly in the slip zone and double interface, but for Ti-6AI-4V alloys, under low stress conditions, the a-phase and b-phase interfaces are relatively weak. Only at high stress levels does the probability of internal nucleation in the slip zone increase significantly, and increasing test temperature has a similar effect. To improve fatigue performance, for a+b titanium alloy rods, it is generally desired to obtain small equiaxed a+b titanium alloy rods, b arrangement, and the b phase is preferably in a free state to reduce the a/b phase interface area. In addition, the fine-grained grains slide relatively smoothly, and the slip free path is short, which can reduce the stress concentration caused by dislocation buildup; At the same time, fine-grained grains also have a greater restraining effect on the calves. In contrast, the coarse-grained Widmanstattennite structure has low fatigue strength due to easy fatigue crack nucleation. Effect of grain size on the 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 depends mainly on the crack growth rate at this time, while the experimental results of pure titanium show that the growth rate of cracks does not have a close relationship with the grain size.
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