1. Influence of alloy composition:
The alloy elements and their addition amount determine the amount of alloy phase in the alloy and thus the microstructure type that can be obtained without heat treatment. The effects of oxygen on fracture toughness were most obvious in the stable elements of titanium alloy. The increase of oxygen content makes fracture toughness drop sharply. Aluminum increases the strength of the alloy but decreases its toughness. The addition of stable elements also increases strength and reduces toughness. The role of Mo is the most obvious, followed by V, followed by Nb. However, it is worth noting that most of the ectopic stable elements can prevent the generation of subcritical cracks, among which Mo has the best effect, while neutral element Zr has little effect. In addition, interstitial hydrogen also has an influence on fracture toughness, which can significantly reduce the resistance of subcritical growth. It is known that the fracture toughness of titanium alloy is higher than that of coaxial tissue, but it must be pointed out that their hydrogen content should not exceed 0.005~0.006. If the hydrogen content is greater than 0.03%, the negative effect of hydrogen is obvious. In the flaky tissue, the fracture stress decreases sharply when hydrogen content is 0.15%. Compared with coaxial tissues, hydrogen diffusion is easier in flaky tissues.
2. Effects of heat treatment
Thermal mechanical treatment also plays a decisive role in the toughness of titanium alloy. High strength and good plasticity of the isometric structure. The strength and plasticity of the coarse equiaxed structure were lost. The flaky tissue has the worst strength and shape. But the fracture toughness of the coarse tissue is higher than that of the fine tissue. The main reason for this difference is the number of cracks in the crack tip area and the degree of deflection of the crack.