The Effect Of Nano-Y₂O₃ On The Microstructure And Property Of Ti-48Al-2Cr-2Nb

As a new type of lightweight high temperature structural material,TiAl alloy possesses high specific strength and specific modulus,good creep resistance and corrosion resistance,low density.So it has wide application prospects in the field of aerospace and automobile industry.However,the microstructure of traditional casting TiAl alloy is coarse and its high temperature strength is low.Therefore,improving the microstructure of TiAl alloy and its high temperature mechanical properties is one of the most important directions of TiAl alloy research.In this work,the mechanical properties of the alloy were improved by adding nano-Y₂O₃ and heat treatment in the Ti-48Al-2Cr-2Nb alloy smelting process.Meanwhile,The phase transformation in heating and cooling process,The effect of nano-Y₂O₃ adding on microstructure and properties of alloy,precipitation phase and the heat treatment have been investigated systematically.In this work,Ti-48Al-2Cr-2Nb buttons with different nano-Y₂O₃ content were produced by water-cooled crucible vacuum induction shell melting furnace.The result shows that the addition of nano-Y₂O₃ can improve the room temperature and high temperature tensile strength of the alloy,and with the increase of nano-Y₂O₃,the room temperature and high temperature tensile strength of the alloy increase first and then decrease.The alloy with 0.05% nano Y₂O₃ has the best mechanical properties.The tensile strength at room temperature can be increased from 379 Mpa to 646 Mpa by the original Ti-48Al-2Cr-2Nb alloy.The tensile strength of the alloy with 0.05% nano-Y₂O₃ at 600? is 669 Mpa and the tensile strength at 650? is 716.3 Mpa,the tensile strength at 700 ° C is 703.8 MPa.The research result of the phase transformation in heating and cooling process shows that the addition of nano-Y₂O₃ in Ti-48Al-2Cr-2Nb alloy will affect the phase transition temperature.Ti-48Al-2Cr-2Nb alloy added with 0.05% Nano-Y₂O₃ will increase the transition temperature of ?2/? phase ?? phase,??? phase+liquid phase and ?-phase+liquid phase?? phase,but will reduce ? single-phase temperature and ?Phase?liquid phase transition temperature,so that ?+?2/? phase and ? phase + liquidphase zone temperature range becomes smaller.The research result of the microstructure of the alloy shows that the addition of nano-Y₂O₃ can refine the grain size of Ti-48Al-2Cr-2Nb alloy.The addition of 0.05%nano-Y₂O₃ can make the average grain size of Ti-48Al-2Cr-2Nb alloy reduced from650?m to 170?m.The addition of nano-Y₂O₃ will refine the ?2/? layer spacing of Ti-48Al-2Cr-2Nb alloy.The ?2/? sheet spacing of the Ti-48Al-2Cr-2Nb alloy with the addition of 0.05% nano-Y₂O₃ alloy was refined from the original 560 nm to 160 nm.The research result of the precipitation phase shows that the existence of yttrium-rich phase in the alloy will change with the addition of nano-Y₂O₃.In the Ti-48Al-2Cr-2Nb alloy with 0.025% nano-Y₂O₃ addition,the yttrium-rich phase exists in the form of block,and its chemical composition is Y₂O₃.With the increase of the amount of nano-Y₂O₃ to 0.05%,The shape of the yttrium--rich phase in the alloy changed into block+lump.When the amount of nano-Y₂O₃ increase to 0.075%,The shape of the yttrium--rich phase in the alloy changed again,into dendritic+fishbone+feather,and its branches are very sharp;the shape of the yttrium--rich in the alloy with 0.1%nano-Y₂O₃ is the same as the addition of 0.075% nano Y₂O₃ alloy.The research result of the heat treatment of the alloy shows that when the tempering time is 3h,the final structure of the alloy is two-state structure.When the tempering time is 6h,the final structure of the alloy is near-lamellar structure.When the tempering time is 9h,final structure of the alloy is full-lamellar structure.The morphology of the yttrium-rich phase in the alloy during the heat treatment will change obviously.With the increase of the heating time at high temperature,the yttrium-rich phase in the alloy gradually spheroids,the shape of yttrium-rich phase in the alloy with0.05% nano-Y₂O₃ gradually changed from the original block+bar to blocks+spherical.And the shape of yttrium-rich phase in the alloy with 0.075% nano-Y₂O₃ gradually changed from the original sharp of fishbone+feather+dendritic to blocks+spherical.