Microstructure, Metal-Mold Reaction and Fluidity of Investment Cast-TiAl Alloys

Abstract

The objective of this study is to investigate the effects of mold preheating temperature on microstrcutural evolution, metal-mold reaction and fluidity of TiAl alloys. A conventional induction melting furnace was used for melting and casting of TiAl alloys in the present investigation. The previous research showed that metal-mold reaction of titanium castings was inevitable during titanium casting. However, there is no metal-mold reaction of TiAl alloys castings regardless mold materials. These results were supported by the experimental results and thermodynamic calculations. However, the grain size of TiAl alloy castings is gradually reduced with mold preheating temperature due to heterogeneous nucleation near outside of mold and diffusion of metallic element from the mold and binder. A fused Al2O3 is promising mold for investment casting of TiAl alloys because of low cost, good strength and thermal stability. The fluidity length of TiAl alloys is increasing gradually with mold preheating temperature. However, it is difficult to predict the accurate applicable limit of preheating temperature of Al2O 3 mold for investment casting of TiAl alloys due to the relationship between metal-mold reaction and fluidity. Therefore, mold material, binder and mold preheating temperature are the most important process parameter of TiAl alloys investment casting.