Effect of fabrication process on microstructure of high Nb containing TiAl alloy

Ti-45Al-8.5Nb-(W,B) (at.%) alloys were fabricated by ingot metallurgy (IM) and elemental powder metallurgy (EPM) processes, respectively. The effect of fabrication process on microstructure of high Nb containing TiAl alloy was investigated. The results showed that IM alloy has near lamellar (NL) microstructure composed of coarse lamellar colonies with a lamellar spacing of about 700nm and equiaxed gamma phase existing at the boundaries of lamellar colonies. While EPM alloy has fully lamellar (FL) microstructure with a lamellar spacing of about 180 nm. A small amount of beta phase exists either at the boundaries of the lamellar colonies or in the lamellar colonies in platelet or blocky morphology in IM alloy. However, the micro-segregation does not exist in EPM microstructure. Borides appear in both the microstructures, but their sizes are smaller in EPM microstructure. HIP treatment can significantly eliminate pores and decrease the beta phase in IM alloy. It is regretful that HIP treatment can only decrease porosity to some extent, but cannot completely eliminate pores in EPM alloy. (c) 2007 Elsevier B.V. All rights reserved.