Interfacial reactions between Ti-1100 alloy and CaO crucible during casting process

Ti-1100 alloys were melted in a controlled atmospheric induction furnace equipped with a CaO crucible. The microstructure, chemical composition, microhardness and metal crucible interfacial reactions were systematically investigated. The results demonstrate that the primary solidification microstructure in the as-cast alloys was the typical Widmanstatten structure. The interactions between crucible and molten alloys are attributed to slight chemical dissolution and weak physical erosion. According to the line scanning analysis, the interfacial layer (alpha-case) thicknesses of Ti-1100 samples in the bottom and side wall are about 18 and 17 mu m, respectively, which are slightly lower than those presented from microhardness tests (25 and 20 mu m). The formation of alpha-case was caused by interstitial oxygen atoms. The standard Gibbs energy of reaction CaO(s)=Ca+O for Ti-1100 alloy was also determined. The equilibrium constant and the interaction parameter between calcium and oxygen were obtained as lg K=-3.14 and e(O)(ca) =-3.54.