High Temperature Deformation Behavior Of TC4 Titanium Alloy With Different Grain Sizes

The deformation behaviors were quite different for titanium with different grain sizes and the microstructure and performance of titanium is relatively sensitive to the process parameters in hot deformation processes. So studying of plastic deformation behaviors and microstructural evolution during hot deformation can provide scientific found and theoretic direction for determining the process parameters and controlling the properties of work pieces.The room-temperature compression behaviors and hot deformation behaviors of TC4 titanium alloy with different grain sizes of 6μm, 12μm and 20μm were studied. The fracture of room-temperature compression test was observed by scanning electronic microscopy (SEM). Based on the results of hot compression tests, the influence of grain size and deformation conditions on flow stress was analyzed. Microstructural evolutions of the alloys with different grain sizes were investigated by optical microscope (OM), transmission electron microscope (TEM), electron back scattering diffraction (EBSD) and high temperature metallographic microscope. The room-temperature mechanical tests showed that the fracture intensity and hardness increased with the increase of grain size. The compression fracture belonged to mixed type and the fracture surface was smooth. The proportion of dimples increased with the decrease of grain size.The experimental results of isothermal hot compression showed that the flow stress and the flow softening extent increased with the decrease of grain size at strain rate from 10-1s-1 to 10-3s-1. At 10-4s-1, flow stress decreased with the decrease of grain size. Flow stress decreased with the increase of temperature and the decrease of strain rate. The deformation activation energies of TC4 titanium alloy with grain sizes of 6μm, 12μm and 20μm were 360.8 kJ/mol, 368.3 kJ/mol and 387.2 kJ/mol, respectively. They were all higher than the self-diffusion activation energies ofαtitanium alloy andβtitanium alloy, which proved that dynamic recrystallization occurred.Microstructural evolution of TC4 titanium alloy with grain sizes of 6μm and 12μm showed that the angles of grain boundaries altered during deformation and grains still kept equiaxed after deformation, which proved that deformation mechanism was grain-boundary sliding. The grains of TC4 titanium alloy with grain size of 20μm were elongated after deformation and mechanism of intracrystalline deformation was dislocation movement. The high temperature and low strain rate were favorable effects on the proceeding of the dynamic recrystallization. For the TC4 titanium alloy with grain size of 6μm, the softening mechanism was dynamic recovery at 10^-4s^-1.