Research On Mechanical Properties As Well As Deformation And Fracture Mechanisms Of Rolled TC1 And TC2 Titanium Alloy Plates

Titanium alloys are important metallic structural materials developed in 1950s. Due to their high specific strength, good corrosion resistance and high heat resistance, titanium alloys have been widely applied in aeronautical, automotive, biomedical fields, etc. Thus, the development and application of titanium alloys have aroused great attention. Obviously, the research on the microstructures and properties of titanium alloys can provide a reliable theoretical foundation not only for the development of titanium alloys but also for the safety design and reasonable usage of titanium alloy components. For various structural materials, fatigue is one of their main failure forms. The investigation concerning fatigue behaviors of materials is of both academic and practical significance. Therefore, the tensile and high-cycle fatigue behaviors of the TC1 and TC2 titanium alloy plates with different rolling direction have been investigated, meanwhile the effect of testing temperature and rolling direction on the tensile and high-cycle fatigue properties of the TC1 and TC2 titanium alloy plates has also been determined.The results of tensile tests show that the tensile properties of the TC1 and TC2 alloy plates strongly depend on the testing temperature. With the increasing testing temperature, both the ultimate tensile strength and yield strength of these two rolled alloy plates decrease, while the fracture elongation of the alloy plates increases. The rolling direction has regular effect on the tensile properties of these two alloy plates. With the same testing temperature, the ultimate tensile strength and yield strength of the TC1 and TC2 alloy plates vertical to the rolling direction are higher than those of the TC1 and TC2 alloy plates parallel to the rolling direction, respectively. While the fracture elongation of the TC1 and TC2 alloy plates vertical to the rolling direction is lower than that of these two alloy plates parallel to the rolling direction. In addition, the comparison of the tensile properties between the TC1 and TC2 alloy plates at the same testing temperature and rolling direction indicates that with the same testing condition, the ultimate tensile strength and yield strength of the TC2 alloy are higher than those of the TC1 alloy, while the fracture elongation of the TC2 alloy is lower than that of the TC1 alloy. The results of high-cycle fatigue tests reveal that the high-cycle fatigue lives of the TC1 and TC2 alloy plates with different rolling direction exhibit regular characteristics with the gradually increasing testing temperature. The high-cycle fatigue life and fatigue limit of the TC1 and TC2 alloy plates both vertical and parallel to the rolling direction decrease with the increasing temperature. In addition, the rolling direction has slightly different effect on the high-cycle fatigue life and fatigue limit of these two alloy plates. For the TC1 alloy plate, with the same testing temperature, the high-cycle fatigue life and fatigue limit vertical to the rolling direction are both higher than those parallel to the rolling direction. For the TC2 alloy plate, with the testing temperature of 25℃and 200℃, the fatigue life and fatigue limit of the alloy plate vertical to the rolling direction are both higher than those of the alloy plate parallel to the rolling direction. When the testing temperature increases to 300℃, the fatigue life of the TC2 alloy plate vertical to the rolling direction is still higher than that of the alloy plate parallel to the rolling direction in the high cyclic stress region, while the fatigue life of the TC2 alloy plate vertical to the rolling direction is lower than that of the alloy plate parallel to the rolling direction in the low cyclic stress region. Meanwhile, with the testing temperature of 300℃, the fatigue limit of the TC2 alloy plate parallel to the rolling direction is slightly higher than that of the alloy plate vertical to the rolling direction. The comparison of the high-cycle fatigue data between the TC1 and TC2 alloy plates reveals that the high-cycle fatigue life and fatigue limit of the TC2 alloy plate is higher than those of the TC1 alloy plate with the same testing temperature and rolling direction.The results of the SEM analysis on the fatigued fracture surfaces indicate that for the TC1 and TC2 alloy plates both vertical and parallel to the rolling direction, the fatigue cracks all initiate transgranularly at the surface of samples and propagate in a transgranular mode at different testing temperature. With the different testing temperature and maximum cyclic stress, the dislocation configuration of the TC1 and TC2 alloy plates vertical to the rolling direction after fatigue deformation exhibits complicated configuration characteristics such as uniform distribution, network distribution, cellular structure, etc. While the microstructure of the TC1 and TC2 alloy plates parallel to the rolling direction after fatigue deformation emerges a large number of dislocation arrays which can promote the initiation and propagation of the cracks.