Effect of TiB2 addition on microstructure and fluidity of cast TiAl alloy

Effects of TiB2 addition on Microstructure and Fluidity of Ti-48Al-2Cr-2Nb + xTiB(2) (x = 0.18, 0.36, 0.54, 0.72, 0.9, 1.8 wt%) alloys fabricated by vacuum non-consumable tungsten arc melting were investigated. Results showed that with adequate TiB2 addition (0.72% TiB2 and more), the as-cast microstructure transformed from coarse columnar grains to fine equiaxed grains, and the grain size was reduced from 800 mu m to 200 mu m. The morphology of borides transformed from flake to block and needlelike, resulted from the dissolution and reprecipitation of original TiB2 powders. The fluidity of TiAl alloy was improved by the addition of TiB2, and the T4822-0.72TiB(2) alloy showed the largest filling length of 266.5 mm, 17.4% higher than that of the matrix alloy. The enhancement of fluidity and the cessation mechanism of melt flow for the TiB2-containing TiAl alloy were analyzed and discussed in light of the microstructure evolution, borides and solidification characterization.