The Effect Of Y On The Microstructure And Room Temperature Property Of As-Cast Ti-48Al-2Cr-2Nb

TiAl alloy is a new kind of light high-temperature structural material.It has a high specific strength,good creep resistence,good corrosion resistence,low density and good flame retardant,etc.So,it is expected to be used in aeroengine flade, automobile booster turbine,gas turbine and replace the Ni-based alloy and expensive flame retardant titanium alloy during 600⁹00℃,and reaching the purpose what could reduce engine’s weight and raise the response rate of booster turbine.Finally,decreasing the energy consumption and raising the engine’s performance.But,TiAl alloy has a defect which can lead to difficult for engineering applicant,that is room temperature brittleness.This paper choose Ti-48Al-2Cr-2Nb developed by GE as experimental material,which had applied in engine of Boeing 787 succefully,using the method of alloying through adding different contents of Y contained in master alloy and nanometer-scale Y₂O₃ respectively and heat treatment method to modify the microstructure and performance,trying to find the appropriate method to improve its microstructure and performance.Analysing the testing results by OM,SEM,XRD and so on.Y element could refine the grain size effectively. The precipitate of alloy adding master alloy containing Y is Y₂O₃,they could hinder the growth of grain during solidification,thus refining the grain size;with increasing of Y contents,the amount of precipitates is increasing and its shape is changing.The precipitate would connect to net when the Ycontents reach to 0.8at%,and hardness of alloy is increasing,too.But the strength and elongation rate would rise first and then decrease.The strength and elongation rate reach peak when Ycontens is 0.1at%.It could refine the grain size and promote the growth of bulk shaped γ through adding nanometer-scale Y₂O₃.The precipitate of alloy is still Y₂O₃;Compared to adding master alloy,the grain size of alloy adding nanometer-scale Y₂O₃ is smaller when the Ycontents of alloy are equal,and strength and elongation rate are higher;The hardness,strength and elongation rate both get high first and then get low with increasing of addition amount of nanometer-scale Y₂O₃;the formation mechanism of precipitate Y₂O₃ in alloy adding nanometer-scale Y₂O₃ is different from alloy adding master alloy containing Y,the former is dissolving-precipitation mechanism and the latter is through Y react with Al2O3 to produce Y₂O₃.A appropriate heat treatment could make the way of alloy’s deformation from pure elastic deformation change into plastic deformation.With increasing of temperature of heat treatment,grain size get bigger,and the evolution of microstructure is “NL�'FL�'coarse FL”.Heat treatment do not change the kinds of phase,but with increasing of heat treatment temperature,the shape of precipitate changed from shape with sharp angle to shape with blunt angle;the precipitate gathered during heat treatment,and some grow up into regular-geometric-shape precipitate,some cluster on boundary thus deteriorate the performance. With increasing of temperature of heat treatment,the hardness,strength and elongation rate both get big first and get smalllater;the way of deformation is plastic deformation after alloy heat treat as 1370℃,8h,FC.