Research On The Casting Property And Processing Technology Of High Niobium Containing Titanium Aluminides Based Alloys

High Nb-TiAl alloy as a new generation of TiAl alloy, which has many excellentproperties such as high specific strength and elasticity modulus, better oxidationresistance and creep resistance and higher application temperature(above850℃), isconsidered to be the most potential light-in-weight high temperature structuralmaterial for the future aviation and aerospace industry. Nevertheless, TiAl alloys havepoor casting properties which lead to low yield and high cost in practical industrialproduction, thus it is difficult to achieve large-scale application.Blade is one of the key components of the aircraft engine. This paper researcheson the casting property and processing technology of high Nb-TiAl alloy in order toobtain complete structure with defects-free turbine blade casting. Firstly, the meshmethod is used to study the effects of micro-alloy elements addition such as B、Y、Mn and Er on the mold filling property of Ti-46Al-8Nb alloys, to abtain an optimizedalloy composition. Then the finite element simulation software ProCAST is adoptedto simulate the filling and solidification process of high Nb-TiAl blade to optimize itscasting process. Finally, the blade is casted by investment casting.The results showed that micro-alloy elements Y and Mn had significantimprovement on the mold filling capacity of Ti-46Al-8Nb melt,0.5at%Y and1at%Mn addition increased the filling rate by54.5%and48.5%respectively. However,the effect of Er and B addition was not so obvious. The final alloy composition wasdecided to be Ti-46Al-8Nb-1Mn-0.3Y-0.1B in consideration of comprehensiveperformance such as oxidation resistance and plasticity.Three factor and three level orthogonal test was designed according to Niyamashrinkage criterion to study the effect of pouring temperature(1600℃,1650℃,1700℃),casting velocity(0.1m·s-1,0.2m·s-1,0.3m·s-1) and preheating temperature of the moldshell(300℃,400℃,500℃) on the filling and solidification process of the blade. Theresults showed that the order of every experiment factor on target index is pouringtemperature, preheating temperature of the mold shell and casting velocity. And theoptimal casting process is that pouring temperature of the melt is1700℃, preheatingtemperature of the mold shell is500℃and casting velocity is0.3m·s-1which showedthe lowest shrinkage porosity rate. Finally, the blade is casted by investment casting method with the optimezedalloy composition and casting process. The blade structure is roughly complete, thereis slight shrinkage cavity on the center of the top blade and slight misrun on the edgeof the thin-wall part. The numerical simulation results show that it is easy to formisolation liquid phase area on the center of the top blade which leads to shrinkageporosity concentrated here. Meanwhile the results show that the long narrow aera ofthe thin-wall part of the blade is filled in the end of the filling process, thus airentrapment is likely to happen which results in misrun. The simulation results are ingood agreement with practical casting.