Hot Deformation Behavior And Processing Map Of Titanium Alloy TC21

Titanium alloy TC21 as a new type of tolerant titanium alloy with high strength,high toughness and low crack growth rate, it is the important structural material in aeronautical field. In this paper, isothermal constant strain rate compression experiment of titanium alloy TC21 has been carried out in the temperature range of 760℃~920℃and strain rate range of 0.001s-1~10s-1, by analyzing the true stress-strain curves at different deformation temperature and strain rate, the constitutive equation of titanium alloy TC21 deformed at high temperature was constructed; The processing maps of titanium alloy TC21 were drawn, the forging processes for titanium alloy TC21 have been optimized, The studied results are of some guidance significance to making reasonable forging processes of titanium alloy TC21.The true stress-strain curves of titanium alloy TC21 are type of strain softening in general, the flow stresses of titanium alloy TC21 decrease with increasing deformation temperatures and decreasing strain rates, it on deformation temperature and strain rate are sensitive, and the sensitivity of the high strain rate is greater than that sensitivity of low strain rate. It was found that the applicability of the Arrhenius equation for titanium alloy TC21 was poor. In view of this, in this paper, the constitutive model of titanium alloy TC21 deformed at high temperature was proposed, the model coefficients were obtained by multivariate linear regression method. Error analysis indicated that the constitutive equations have high precision, the average errors of flow stress between experimental and calculated value is 7.64%, The constitutive equation can well describe the hot flow behavior of titanium alloy TC21.The processing maps of titanium alloy TC21 have been plotted by using Prasad criterion, Murty criterion and Malas criterion, respectively. Found the Murty criterion is more accurate than Prasad criterion and Malas criterion by observation of microstructure. The predicted results by using the processing maps based on Murty criterion combined with observation of microstructure are the following. The instable regions of plastic flow are in the temperature ranges and the strain rate ranges of 760℃~780 ℃ and 0.008s-1~10 s-1, 780 ℃ ~810 ℃ and 0.03s-1~10s-1, 810 ℃ ~850 ℃ and0.1s-1~10s-1. The manifestations of flow instability including 45 ° macroscopic shear crack, adiabatic shear bands and flow localization; The better thermomechanical parameters for hot deformation are in the temperature ranges and the strain rate ranges of 860℃~910℃ and 4s-1~10s-1, 855℃~913℃ and 0.001s-1~0.008s-1. The deformationmicrostructure of the parameters in this regions exhibits some of the globular alpha phase and crooked alpha phase, and this is a transitional deformation mechanism. The optimum thermomechanical parameters for hot deformation are in the temperature ranges and the strain rate ranges of 875℃~895℃ and 7s-1~10s-1, 880℃~910℃ and near 0.001s-1. and the corresponding main deformation mechanism in these regions is globularization of slices alpha phase.