Thermodynamic and Kinetic Consideration of Selecting Mould Materials for Casting Titanium Alloys

摘要

The benefits of excellent properties in combination with the process flexibility make titanium alloy castings multiplicately utilized in many fields. An important basis during casting process must ensure of which the control or elimination the interaction between mould and molten metal. After comment the molten titanium alloys thermodynamically, the ΔG of interactions of some refractory oxides mould materials with molten titanium alloys have been calculated as considering the effects of mould materials, alloying constituents and melt temperature. Based on the analyzing mechanism of interface reactions, it has been found that the reaction is composed of two periods as decomposition and solution of mold materials, and diffusion. Accordingly, a kinetic model including decomposition-solution and diffusion of mold materials has been established. Results showed that the formation of the surface reaction layer of titanium alloys was not only related with the chemical stability of mould materials but also markedly influenced by interfacial heat transfer characteristic. A near directional heat-transfer method can predict interaction between titanium alloys and mould materials experimentally. Casting parameters including cooling rate, sorts of mould and additional constituents have different effects on interfacial reactions.