Study On The Hot Deformation Behavior And Microstructures Of TA19 And TC17 Alloys

TA19 and TC17 alloy are used for aeroengine and belong to difficult-to-deform materials, which show extremely sensitivity to the hot processing parameters, such as the temperature, strain and strain rate. It is easy for the formation of the defects during the deformation of these alloys, which will influence the mechanical properties of these alloys. The forging processes for these two alloys have been optimized by hot compression tests and using processing map technology, which have great signi-fycance in improve the properties of materials, depress cost and reduce research cycle.In this work, the high temperature deformation behavior of the near-alpha titanium alloy TA19 and the near-beta titanium alloy TC17 have been studied by hot compressing tests. The flow behavior was described by the constitutive equation, the deformation activation energy were calculated. The microstructures of specimens were studied by the optical microscope, the scanning electron microscope and the transmission electron microscope. The effect of the deformation temperature, strain and strain rate on the microstructure of specimens and mechanism were analyzed. The processing maps of TA19 and TC17 alloy were plotted by Dynamic Material Model and the principle of system stability analysis, and the different regime in processing map was analyzed by the microstructure, the hot work ability was studied profoundly and the deformation parameters were optimized. From this work, it was found that:The hot deformation behaviors of TA19 and TC17 alloy were described by the power exponent and hyperbolic sine constitutive equation respectively, and the deformation activation energy of TA19 alloy were calculated to be 586KJ/mol in ?+? phase field and 290KJ/mol in ? phase field. The deformation activation energy of TC17 alloy were calculated to be 407KJ/mol in ?+? phase field and 155KJ/mol in ? phase field. In addition, the flow stress model of TA19 and TC17 alloy were established.TA19 alloy and TC17 alloy are sensitive to the strain. The quantity of globular a phase increases with increasing strain under the Tp, and almost a phase from lamellar to equiaxed at the strain of 80%. The TA19 alloy and TC17 alloy are also sensitive to the strain rate, the quantity of globular a phase increases with decreasing strain rate. Adiabatic shear bands are easy to occur at high strain rate and low temperature field due to the low heat conductivity.Dynamic recrystallization (globularization) is the deformation mechanism of TA19 and TC17 alloy in ?+? phase, though the globularized mechanisms are different. The dynamic recovery which controlled by climb motion and cross slip is the deformation mechanism of TA19 above the transformation temperature and at high strain rate, while the dynamic recrystallization is the deformation mechanism at low strain rate. The deformation mechanism of TC17 at high strain rate above the transformation temperature is also dynamic recovery, while the continuous dynamic recrystallization is the deformation mechanism at low strain rate.Globularization was observed in TA19 alloy at 940?960? and 0.01?0.1s-1, and the efficiency of power dissipation is 45%. The dynamic recrystallization of TA19 alloy was occurred at 980?1000? and the strain rate was 0.01s-1, and the efficiency of power dissipation is 35%. Adiabatic shear bands took place due to the low heat conductivity of TA19 alloy at 940?1000 ? and the strain rate was above 0.535s-1.At 820?850? and the strain rate was 0.01s-1, the microstructure of the specimens of TC17 alloy is spheroidization, and the efficiency of power dissipation is 48%. The dynamic recrystallization of TC17 alloy was occurred at 900?930? and 0.01?0.Is-1, and the efficiency of power dissipation is 39%. Adiabatic shear bands took place due to the low heat conductivity of TC17 alloy at 820-880? and the strain rate was above 0.415s-1.The optimized processing craft was obtained:the optimum processing temperature is in the range of 940?960 ? and the strain rate is in the range of 0.01?0.Is-1 for TA19 alloy. The optimum processing temperature is the range of 820-850? and the strain rate is about 0.01s-1 for TC17 alloy. The efficiency of power dissipations are above 45% in these regions.