Factors that affect the service life of titanium alloy rods!
The fatigue and fracture properties of titanium alloy rods play a crucial role in determining the service life of alloys. For many years, research has been conducted both domestically and internationally to explore the fatigue and fracture mechanisms of titanium alloy rods, as well as their relationships with various metallurgical factors. Due to the complexity of the problem itself and the dispersion of initial experimental data, some substantive issues are still unclear and viewpoints are not fully unified. Here, only some representative conclusions are introduced.
The fatigue life of titanium alloy rods, like other materials, depends on the probability of fatigue crack nucleation and crack propagation rate. According to research on pure titanium, fatigue cracks mostly nucleate within the slip band and at the twin interface. However, for Ti-6AI-4V type alloys, under low stress conditions, the a-phase and b-phase interfaces are relatively weak links. It is only at high stress levels that the probability of nucleating within the slip band increases significantly. Increasing the test temperature also has a similar effect. In order to improve fatigue performance, a-10b type titanium alloy rods are used, Usually, it is desired to obtain small equiaxed A+B tissues, and the B phase is in a free state to reduce the interface area of the A/B phase. In addition, the slip of fine grains is relatively uniform, and the free path of slip is short, which can reduce the stress concentration caused by dislocation accumulation; At the same time, fine grains also have a significant restraining effect on twinning. On the contrary, the coarse-grained Weinstein structure has lower fatigue strength due to its easy nucleation of fatigue cracks. The effect of grain size on the fatigue performance of smooth and notched Ti-6A1-4V alloy specimens.
In the presence of notches and stress concentration, the influence of grain size decreases, as the fatigue life mainly depends on the crack propagation rate, while the experimental results of pure titanium show that the crack propagation rate is not closely related to grain size.
