Effects of Boron Addition on Grain Refinement in TiAl-based Alloys

W.D. Wang,Y.C. Ma,B. Chen,M. Gao,K. Liu and Y.Y. Li Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China

摘 要：Solid state phase transformation characteristics of the body centred β（Ti） into the hexagonal closed packed α（Ti） in Ti45Al8Nb-（0, 0.3, 0.5 and 0.8 at. pct） B alloys were investigated by heat treatment to clarify γ/α2 lamellar microstructure refinement induced by B addition. Experimental results confirmed two kinds of boron-reduced grain refinement mechanisms through refining either β phase then α phase （β-refinement） or α phase directly （α-refinement） to refine lamellar microstructure at room temperature; however, the role of α-refinement dominated the as-cast lamellar microstructure refinement over β-refinement in Ti45Al8NbxB alloy. It was also found that during the α-refinement the convoluted flake- and plate-like borides along β grain boundaries assisted nucleation of α phase, and the particle-like borides near β grain boundaries impeded α phase growth.

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