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The influence of Hf and B on the solidifi cation structure of cast Ti-46Al alloys was investigated.The results show that the coupling effect of Hf and B changes the solidifi cation structure morphology and strongl ref ines the grain size.When the Hf+B contents were increased from 0 + 0.0 to 3 + 0.2,5 + 0.6 and 7 + 1.0(in at.%),the solidification structure morphology changed from coarse columnar dendrite to fine columnar dendrite then to equiaxed dendrite,and further to f ine near granular grain whilst the average grain size decreased to 20 μm It is concluded that the columnar dendrite refinement is due to the effect of Hf and B on the decrease of A diffusion coeffi cient in the melt.The f ine near granular grain formation is attributed to the combined constitutiona supercooling formed by Al and B segregation that is strengthened by Hf and B additions at the solid/liquid interface during solidifi cation,and the TiB2 precipitates acting as heterogeneous nuclei.
The influence of Hf and B on the solidifi cation structure of cast Ti-46Al alloys was investigated. The results show that the coupling effect of Hf and B changes the solidifi cation structure morphology and strong ref refine the grain size. When the Hf + B contents were increased from 0 + 0.0 to 3 + 0.2, 5 +0.6 and 7 + 1.0 (in at.%), the solidification structure morphology changed from coarse columnar dendrite to fine columnar dendrite then to equiaxed dendrite, and further to ine ine granular grain whilst the average grain size decreased to 20 μm It is concluded that the columnar dendrite refinement is due to the effect of Hf and B on the decrease of A diffusion coeffi cient in the melt.The f ine near granular grain formation is attributed to the combined constitutional supercooling formed by Al and B segregation that is strengthened by Hf and B additions at the solid / liquid interface during solidifi cation, and the TiB2 precipitates acting as heterogeneous nuclei.