Recrystallization Behavior Of Forged Ti-43Al-9V-Y Alloys During Hot Deformation

Although the performances of TiAl-based alloys were known as high specific strength,oxidation resistance and creep resistance,poor hot workability limited the application of traditional TiAl-based alloys.A large number of high-temperature as well as disordered ? phase can be retained by adding stable elements ? phase in the alloys,which can greatly improve the hot-workability.In the hot-working process,reasonable control of thermal processing parameters becomes the key to obtain an ideal microstructure.In this paper,the forged beta+gama TiAl alloys with a nominal composition of Ti-43Al-9V-Y was selected to systematically study the dynamic recrystallization behavior of the alloy during high-temperature deformation and and the static recrystallization behavior during annealing.The microstructure and mechanical properties of the forged Ti-43Al-9V-Y alloy were studied.The forged TiAl alloys in this article were mainly composed of ?/B2,of which the content is 18.2%,and ? phase;The microstructure was mainly composed of(?/B2)/? layers,equiaxed ?-crystals and large-sized ?/B2 phases..There was obvious directionality in mechanical properties of TiAl alloy after forging.At 750°C,the strength of the alloys in the forging direction reached 497 MPa,the elongation was 40%;the strength of the alloys perpendicular to the forging direction was 475 MPa,and the elongation was only 2.2%.The thermal compression simulation experiment was used to study the high-temperature deformation behavior of the forged TiAl alloys.Through observation of the deformed microstructure,the dynamic microstructure of the as-forged TiAl alloys was obviously recrystallized,and the original B2/? layer gradually was substituted by recrystallized grains at the temperature of 1050°C ~1150°C with 60% deformation of microstructure.At the temperature of 1200°C,the microstructure evolution during the high-temperature deformation of the alloy was dominated by the phase transformation of ? phase and ? phase to ? phase,and the microstructure obtained after thermos compression was more homogenous.Based on the obtained stress and strain data under different deformation parameters,the thermal deformation activation energy of the as-quenched TiAl alloys was calculated to be Q=633 k J/mol,and a phenomenological constitutive equation was constructed.At the same time,the dynamic recrystallization critical dynamic model and dynamic recrystallization kinetic model of forged TiAl alloy were established.The effects of various deformation parameters on the dynamic recrystallization behavior of the as-quenched TiAl alloy at high temperature was then systematically studied.The general rule of the dynamic recrystallization of the as-forged TiAl alloywas analyzed from the perspective of the structure by means of EBSD.The evolution of tissue during isothermal annealing of different tissues after thermos compression was studied.The results showed that the microstructure obtained after thermos compression at 700°C can still remain stable;increasing the annealing temperature and the holding time help to accelerate the decomposition of coarse structure and the growth of fine grains;increasing the holding time can't significantly affects the acceleration of evolution of the tissue when the temperature is lower.