Fundamental Research On Isothermal Die Forging Of High Nb-TiAl Alloy

Due to the low room-temperature ductility, poor hot deformability and narrow processing window lead to difficult hot-deformation. In the process of carrying out the isothermal die forging of the high Nb-Ti Al alloy blade of the high pressure compressor of a certain aero engine, it is necessary to understand the high Nb Ti Al alloy hot deformation behavior and microstructure evolution and the distribution law of stress and deformation quantity reasult from the plastic deformation. This paper is a study on the high temperature deformation behavior of hi gh Nb-Ti Al alloy forging blade, including research on microstructure and forming properties.By means of thermal physical simulation and ABAQUS/Explicit, the rheological behavior of alloy materials, processing hardening, softening behavior, equivalent stress field and equivalent effect field and microstructure evolution of the alloy were investigated between 900℃ and 1000℃ in strain rate range 0.005s-1~0.05s-1 and deformation quantity of 15%~50%, different billet shape. Based on the dynamic materials model(DMM), the hot processing maps of the alloys were established.In the high Nb Ti Al alloy hot processing map, regardless of the temperature and the power dissipation efficiency η in high strain rate region will become very low. High Nb-Ti Al alloy flow instability region is distributed at low deformation temperature and high strain rate region. With the increase of deformation amount, the flow instability region gradually to high deformation temperature and low strain rate spread.The simulation results show that the microstructure of high Nb-Ti Al alloy is affected obviously by deformation, deformation temperature and strain rat e. High deformation temperature and low strain rate can decrease the deformat ion resistance of the material. It can effectively improve the hot processing of high Nb-Ti Al alloy. The blank shape with appropriate amount of deformation and high matching degre e can improve the filling ability of the isothermal die forging process, and weaken the internal stress caused by the deformation of the material, and prolong the service life of the parts. The most suitable parameter combination is A blank, deformation temperature ≥930, strain rate ≤0.01s-1, deformation quantity ≤35%.According to the optimal isothermal die forging process, isothermal die forging of high Nb-Ti Al alloy blade is carried out. The shape and size of blade is complete, without macroscopic defects. The large deformation of Nb-Ti Al alloy blade is rough selvedge and the joints between blade and tenon. The stress distribution and strain distribution are the same.The blade central position of the content of α2 phase was 12.3%, γ phase was 83.5%, and β/B2 phase was 4.1%. The distribution of α2 phase and γ phase which is small is uniform. The lamellar spacing is significantly refined result from isothermal forging. The grain size is below 10μm, and the grain boundary in small angle is increased. The microstructure of the heart and rough selvedge is different, crystal layer and equiaxed of rough selvedge are flattened elongated along the flow direction, the flow line direction is highly consistent. There are 1μm grain below 10% in the rough selvedge of the blade, and the flow of the blade is less than that of the edge of the blade. Forging streamline is extraordinarily obvious.