Because of its high specific strength, light weight, wide operating temperature range and excellent corrosion resistance, titanium alloy is widely used in aerospace. Currently, titanium alloys used in aerospace field account for about 70% of titanium production. High purity titanium has good plasticity, but when the content of impurity exceeds a certain amount, brittle compounds will be formed, so that the plasticity of titanium alloy drops sharply. The microstructure of titanium alloy is an important factor that determines its tensile strength, fatigue strength and fracture toughness. Its structure is mainly composed of alpha and beta phases, and its morphology can be divided into wei's, net basket, bistate and equiaxial structure.
(1) tensile properties
Coarse alpha phases are generally distributed on the original beta grain boundary, and such coarse original beta grains are generally present in the weiermann structure and distributed in roughly parallel weiermann alpha bars. The room temperature plasticity of weissner structure is generally the worst because the grain size of the structure is very large. Dimorph tissues are generally composed of relatively small primary alpha phase and beta transition tissues. If the dimorph tissues obtained by "solid solution + aging" treatment have a stronger tensile strength at room temperature than the other three tissues.
(2) fracture toughness and crack growth rate
In general, the fracture toughness of weissner tissues is greater than that of equiaxed alpha and bimorphic tissues. The fracture toughness of the alloy is greatly affected by the number and size of the primary alpha phase.
(3) fatigue performance
Among the above four different types of tissue, the fatigue limit of equiaxial tissue is the largest, and the fatigue limit of weissner tissue is the worst. Secondly, for the same alloy, the two-state structure has the best fatigue performance, and the weissner structure has relatively poor fatigue performance, no matter it is low cycle fatigue or high cycle fatigue.
(4) thermal stability and creep resistance
The so-called heat-resisting titanium alloy means that the alloy has good thermal stability. However, due to the poor heat resistance of the beta phase, there are generally only a small amount of beta alpha alloy and alpha + beta alloy in the thermo-strong titanium alloy. The creep resistance is mainly affected by tissue morphology. Among the four kinds of microstructure, the creep property of equiaxed microstructure is poor because the grains are small and the interfaces are many. Although the widmanstatten structure has high creep resistance, but its organization of grain is very thick and bulky grain boundary alpha, vulnerable to contamination of oxygen, and its itself also has some weaknesses, and application of titanium alloys at high temperature, generally adopts the comprehensive performance better contain primary alpha than little binary and top organizations.
