Abstract: Research on different boron contents on the grain refinement effect of Ti46Al8Nb alloy was carried out to study the role of boron addition. The experimental results show that there are two ways for the precipitation of boride. When boron content is low and the cooling rate is relatively high, boride exists mostly in inter-dendrite area, showing that boron is pushed forward at the solidification front, and precipitates at last coupling with the dendrite growth. When the boron content is high and the cooling rate is relatively low, boride can exist at the dendrite arm. The observation of the dendrite morphology with different boron addition show that the morphology and the arm spacing of the dendrite are not changed essentially, though the grain size difference can be observed obviously, indicating that boron addition does not influence the solidification process. In the observation of partially grain refined Ti46Al8Nb0.4B alloy, it is found that the unrefined big lamellar and the refined lamella are formed from one same β grain. Besides, the dendrite and the boride morphology in the big grain and small grains are same. All these results show that the boron addition does not influence the solidification process, but promote the β→α transformation, so still grain refined lamella can be gained at last.
Mechanism of grain refinement effect of boron addition on γ-TiAl based alloys
Abstract：
Research on different boron contents on the grain refinement effect of Ti46Al8Nb alloy was carried out to study the role of boron addition. The experimental results show that there are two ways for the precipitation of boride. When boron content is low and the cooling rate is relatively high, boride exists mostly in inter-dendrite area, showing that boron is pushed forward at the solidification front, and precipitates at last coupling with the dendrite growth. When the boron content is high and the cooling rate is relatively low, boride can exist at the dendrite arm. The observation of the dendrite morphology with different boron addition show that the morphology and the arm spacing of the dendrite are not changed essentially, though the grain size difference can be observed obviously, indicating that boron addition does not influence the solidification process. In the observation of partially grain refined Ti46Al8Nb0.4B alloy, it is found that the unrefined big lamellar and the refined lamella are formed from one same β grain. Besides, the dendrite and the boride morphology in the big grain and small grains are same. All these results show that the boron addition does not influence the solidification process, but promote the β→α transformation, so still grain refined lamella can be gained at last.
