Research On Rheological Behaviour And Microstructure Evolution Of TC11 Titanium Alloy

TC11 titanium alloy is a hard-to-deform metal with excellent high and low temperature properties but poor plasticity.Rotary forging is a complex metal forming technology under the coupling of multiple nonlinearities and multiple factors.The local forming characteristics can significantly reduce the forming force of difficult-to-deform metal materials.Hot forming technology can effectively soften the material,reduce the deformation resistance and improve the plasticity.Hot rotary forging technology is one of the most effective methods to achieve high efficiency and low cost manufacturing of TC11 titanium alloy parts.The microstructure evolution of titanium alloy at high temperature is more intense,such as dislocation movement,phase transformation,dynamic recovery and recrystallization,which has great influence on the flow state,microstructure and properties of the material.The research on material flow and microstructure evolution of titanium alloy rotary forging process is the basis and key to make reasonable process and give full play to the potential of process.The isothermal and constant strain rate uniaxial compression tests of TC11 titanium alloy are carried out at the deformation temperature of 900 ～ 1050℃ and strain rate of 0.1 ～ 10/s.The observation of microstructure after deformation shows that there is obvious dynamic recrystallization phenomenon in TC11 titanium alloy during hot deformation.A flow stress high temperature constitutive model based on dynamic recovery and dynamic recrystallization phenomenon is established by combining K-M dislocation density model and dynamic recrystallization fraction model.The correlation coefficient and average relative error are 0.989 and 6.53%,respectively.The model can be used to predict the high temperature rheological behavior of TC11 titanium alloy.The effects of solution temperature and solution time on microstructure and microhardness of TC11 titanium alloy are studied by solution-aging heat treatment test.The results show that the content of equiaxed primary α phase increases with the solution temperature when the solution temperature is below the phase transition point,and decreases rapidly when the temperature reaches the phase transition point;When the solution temperature is 950℃,with the increase of solution time,the grain boundary α phase begins to grow,and the lamellar αphase changes into lamellar and equiaxed α phase structure;When the solution time is fixed,the hardness of TC11 titanium alloy decreases first,then rises slowly and tends to be stable with the increase of solution temperature,and reaches the highest when the solution temperature is950℃ and the solution time is 120 min.Through the hot rotary forging process experiments of TC11 titanium alloy under different preheating temperatures and swinging head feed rates,it is found that under the same feed rate,the higher the temperature,the stronger the flow ability of the material,the easier the deformation and the more complete the mold filling;At the same rotary forging temperature,the material flow is difficult at low strain feed speed(1mm/s),and the radial flow of material on upper and lower surfaces is small;At high feed speed(4-5mm/s),the material flow is uneven.When the preheating temperature is 1150℃,and the feed speed of swinging head is 2mm/s-3mm/s,the forming effect of the sample is better,the upper and lower surfaces of the material flow evenly,and the mold filling is complete.Through the microstructure observation,it is found that the microstructure of the two phases after recrystallization is obtained at 950℃ and the feed rate is 3mm/s.