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 + xTiB₂ (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 μm to 200 μm. The morphology of borides transformed from flake to block and needlelike, resulted from the dissolution and re-precipitation of original TiB₂ powders. The fluidity of TiAl alloy was improved by the addition of TiB₂, and the T4822–0.72TiB₂ 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.