Study On The Dynamic Recrystallization Behavior And Prediction Model Of TA15 Titanium Alloy In The β Hot Process

TA15 titanium alloy is the one of the most important structural materials in the aircraft industry of our country which belongs to a kind of damage tolerance alloy of high aluminum equivalent. Because this alloy would easily appear"grain coarsening"phenomena duringβhot process, while utilizing dynamic recrystallization to control grain size in material microstructure is the key to solve the problem mentioned above. Therefore, in order to systematically obtain the evolution of dynamic recrystallized microstructure of TA15 titanium alloy inβhot process, and then to achieve a good matching between strength,plasticity and damage tolerance properties and guide practical production as well, the dynamic recrystallization behavior and prediction model of TA15 titanium alloy inβhot process have been studied by using isothermal constant strain rate compression tests and metallographic analysis system. The main research contents and conclusion are as follows:The true stress-true strain curves of TA15 titanium alloy compressed under various strain rates have been analyzed, and the results show that the flow stress is sensitive to the strain rates, when the strain rate increases one order of magnitude, the peak stress would increase about 5～20MPa; the rheological curves of low strain rates (0.001s^-1, 0.01s^-1) belong to the type of dynamic recrystallization, and its main softening mechanism is dynamic recrystallization, while the rheological curves of high strain rates (0.1s^-1, 1s^-1) belong to the type of dynamic recovery, and its major softening mechanism is adiabatic effect.The microstructures of TA15 titanium alloy samples compressed under different strain rates and deformations were observed and measured by using metallographic analysis system. The results show that increasing strain rate could refine grain obviously, but different strain rate would bring different degree of grain refinement, the grain size would decrease faster when the strain rates are in the low (0.001s^-1, 0.01s^-1), and on the contrary decrease slower in the high (0.1s^-1, 1s^-1) ; according to the effect of grain refinement and uniformity in the microstructures which deformed under various conditions, the strain rate of 0.01s^-1 is preferable forβhot process; the deformed microstructures of TA15 titanium alloy inβhot process would mainly occur discontinueeous dynamic recrystallization under the lower strain rates, while it mainly occurs continuous dynamic recrystallization during the higher strain rates.According to the theory of recrystallization grain nucleation and growth as well as the basic characteristics of recrystallization kinetics, the theoretical mathematic models of dynamic recrystallization were derived, and base on the results of them the dynamic recrystallization prediction models of TA15 titanium alloy at temperature 1050℃were established firstly. The results indicate that the deformation activation energy of TA15 titanium alloy inβhot process is 313.442kJ/mol, and the relation equation between critical strainε_c and peak strainε_p isε_c=0.8455×ε_p; the calculation formula of critical strain of dynamic recrystallization isε_c =0.1245×Z^0.0718, and among which symbol Z represents Zener-Holloman parameter equation; the concrete expression formula of average grain size of dynamic recrystallization is as follows: d=10.8134×Z^-0.3261μm; and the expression formula of dynamic recrystallization kinetics is as follows: X_dyn=1-exp[-0.1146×(ε-ε_c)/ε_p]1.1998.