J Mater Sci Technol ›› 2010, Vol. 26 ›› Issue (7): 639-647.

• Regular Papers • Previous Articles     Next Articles

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

W.D. Wang, Y.C. Ma, B. Chen, M. Gao, K. Liu, Y.Y. Li   

  1. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
  • Received:2009-06-30 Revised:2009-09-07 Online:2010-07-31 Published:2010-07-26

Abstract:

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 thenα 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.

Key words: Titanium aluminides, Phase transformation, Microstructure