Investigation Of Thermal Deformation Behavior And Fatigue Properties Of TC11Titanium Alloy

TC11titanium alloy becomes the ideal aerial material due to its high specific strength, corrosion resistance, good medium temperature strength and low density. TC11alloy also has some excellent features like steel and aluminum alloy, etc. Lamellar structure TC11alloy is provided with good high heat strength and high tensile strength, but its tensile ductility and fatigue properties are poor. In the production practice, tensile at high temperature is a common means of processing and TC11alloy components often bear the role of fatigue loading. Thus, an investigation of high temperature tensile deformation behavior and fatigue properties at room temperature of TC11alloy has an important theoretical and practical significance.In this paper, TC11alloy with α/β lamellar structure is selected. High temperature tensile tests are conducted to investigate deformation mechanism and microstructure evolution of TC11alloy at different temperatures (700℃to950℃) and strain rates (0.001s-1to4s-1). The alloy is also subjected to tensile and fatigue experiments at room temperature but different thickness of the different samples (0.1mm to2mm). The relationship between the tensile, fatigue properties and the thickness of samples was examined. The results show that:The tensile tests at high temperature reveal that at the same strain rate, the peak flow stress decreases with increasing temperature, while at the same deformation temperature, peak flow stress increases with increasing strain rate. Compared with the strain rate, deformation temperature on the peak flow stress is more obvious. Peak flow stress at700℃each strain rate is almost the same. Evident flow softening happens at950℃.Microstructure analysis shows that at700℃the lamellar structure is deformed by shear banding; at800℃-850℃the lamellar structure is deformed by shear banding and fragmentation of the lamellae; at900℃-950℃fragmentation and globularization become the main mechanism. Cracking and voiding occured along grain boundaries, and that happened within grains with increasing temperature. and the ratio of cracking area to the voiding area shows a trend that first increases and then decreases with increasing temperature. The EBSD analysis shows that at700℃-0.001s-1the Burgers orientation relationship was not destroyed, α/β lamellae shows compatible deformation. At700℃-4s-1the Burgers orientation relationship was destroyed slightly, deformation mainly occured in the β phase. At950℃-0.001s-1the Burgers orientation relationship was destroyed severely, α/β lamellae became fully fragmentation and globularization. At950℃-4s-1the Burgers orientation relationship was destroyed severely, the α/β lamellae became stretched, local fragmentation and globularization.Fatigue tests of TC11samples with different thicknesses show that S-N curves of2mm～0.4mm-thick samples are almost same. The low cycle fatigue properties of2mm～0.4mm-thick samples are better than that of0.2mm～0.1mm-thick samples. High cycle fatigue properties of0.2mm～0.1mm-thick samples are better than that of2mm～0.4mm-thick samples.