Quasi-Static Tensile Behavior Of TA7 TB2 And TC4 Titanium Alloys At Low Temperatures

Titanium alloys have excellent low-temperature properties,and further study on their low-temperature deformation behavior will be helpful to popularize the application of titanium alloys at low temperatures.The quasi-static tensile behavior of TA7,TB2 and TC4 titanium alloys was studied by using a cryogenic mechanical testing device from room temperature to liquid nitrogen temperature.The effects of low temperature and strain rate on the tensile properties were investigated.Based on X-ray diffraction?XRD?,optical microscopy?OM?,transmission electron analysis?TEM?and scanning electron microscopy?SEM?,the deformation and fracture characteristics of titanium alloys were discussed.The series low temperature quasi-static tensile test results show that the tensile and yield strengths of the supplied and annealed TA7 titanium alloys increase significantly with the decrease of temperature,and the elongation decreases,but123K to 77K increased significantly,and 77K was similar to normal temperature.With the increase of strain rate,the strength at room temperature and low temperature of TA7 alloy increases,while the elongation decreases.The strength at strain rate 10^-2s^-1 is about 3%higher than that at 10^-3s^-1,while the elongation is about 19%.The plastic deformation of TA7 alloy depends on dislocation slip from room temperature to liquid nitrogen temperature.The deformation structure of TA7alloy from room temperature to 123K is dominated by short dislocations entangled with each other,while at 77K it is long dislocations parallel to each other.The tensile fracture of TA7 titanium alloy at normal temperature to 77K is macroscopically a ductile fracture,and it belongs to microporous aggregate fracture in the microscopic fracture mechanism.From room temperature to 123K,TA7 alloy exhibits equiaxed dimples,and at 77K,most of them are elongated dimples.From room temperature to 77K,the quasi-static tensile and yield strength of solid solution TB2 titanium alloy increased significantly,the elongation decreased monotonously,the strength at 77K increased by about 110%compared with room temperature,and the elongation at 77K was only about 1%..The room temperature and low temperature strength of TB2 alloy increase with the increase of strain rate,and the elongation decreases.The strength at strain rate of 10^-2s^-1 is about 7%higher than that of 10^-3s^-1,and the elongation is about 20%lower.The quasi-static plastic deformation of TB2 alloy relies on dislocation slip at normal temperature,and 77K is shared by the dislocation slip and twin.At normal temperature to 123K,the tensile fracture of TB2 titanium alloy is macroscopically a ductile fracture,and it belongs to microporous aggregate fracture in the microscopic fracture mechanism.The fracture is composed of equiaxed dimples.The 77K fracture is macroscopically a brittle fracture.The micro-fracture mechanism belongs to the mixed fracture,and the fracture is a mixed fracture between the dimple and the intergranular.Quasi-static tensile and yield strength of annealed and aged TC4 titanium alloys increase with decreasing temperature.From normal temperature to 123K,the elongation rate drops first,and it rises slightly at 77K.With the increase of strain rate,the strength of TC4 alloy increases,the elongation decreases,the room temperature and low temperature strength at strain rate 10^-2s^-1 is about 3%higher than 10^-3s^-1,and the elongation is about 12%lower.The quasi-static plastic deformation of the annealed TC4 at room temperature is mainly the dislocation slip in the?phase,and the 77K is the dislocation slip in the?phase and the twin in the?phase.When the aged TC4 alloy is deformed at low temperature,the equi axed?phase is elongated along the tensile direction,and the dislocation slip occurs in the?phase,while the secondary flaky?phase in the?transformation matrix is turned to the stretching direction,and the flaky?phase at 77K Produce twins.The room temperature and low temperature fractures of TC4 alloy show ductile fracture characteristics,and the micro-fracture micro-pore aggregation characteristics are significant,still consisting of equiaxed dimples,and there is a step surface at 77K fracture.