The characteristics of high-temperature titanium alloy mold precision casting technology - microstructure analysis

At present, the research on the high-temperature titanium alloy mold precision casting technology for long-term use at 600°C and short-term use above 600°C is still in its infancy. Compared with ordinary titanium alloys, the high-temperature titanium alloy mold precision casting technology has its own difficulties, mainly including the difficulty in controlling the composition and solidification structure during the casting process due to the presence of more alloying elements and higher contents, the more complex interaction between the melt and the ceramic mold shell surface material, the poor flowability of the melt at normal casting temperatures, and the lack of casting performance parameters.

In view of the characteristics of the 600-700°C high-temperature titanium alloy mold precision casting technology, this chapter will focus on introducing several aspects of this technology, including the mechanism of the interaction between the high-temperature titanium alloy melt and the oxide ceramic mold shell interface, the filling and solidification laws of the high-temperature titanium alloy melt under centrifugal force field conditions, the composition control and microstructure performance of high-temperature titanium alloys, and the development of typical high-temperature titanium alloy castings. To ensure uniform composition, except for special cases where the raw materials for remelting high-temperature titanium alloys are used, they are all prepared by the induction shell melting (ISM) technology.

Interaction mechanism between the high-temperature titanium alloy melt and the oxide ceramic mold shell interface Under high temperatures, the titanium alloy melt is very active and almost reacts with all refractory materials. Therefore, whether in the melting or pouring process, the interface interaction between the alloy melt and refractory materials is a universal phenomenon. This interaction can lead to the generation of some casting defects, such as surface contamination of the castings, pores, and inclusions, which reduce the quality and performance of the castings. Obtaining the interaction laws between the high-temperature titanium alloy melt and the oxide ceramic mold shell interface, revealing the interaction mechanism between the melt and the surface layer of the mold shell, is of great significance for the development or production of high-quality complex thin-walled high-temperature titanium alloy castings.

Interaction laws between the melt and the mold shell surface layer
> The surface layer refractory materials directly contact the molten titanium alloy, and their own properties have a significant influence on the degree of interface interaction. Currently, oxide refractory materials are widely used in the preparation of mold shells for high-temperature titanium alloy mold precision casting. The standard Gibbs free energy of oxide can be used to compare the relative stability of oxides. The larger the negative value of the Gibbs free energy of the oxide formation reaction, the more stable the formed oxide is, and titanium is oxidized to form TiO. The high standard Gibbs free energy of oxide formation is not necessarily completely corresponding to the strength of the interface interaction between the oxide refractory material and the titanium alloy melt. When studying the interaction, the influence of the dissolution of the oxide refractory material must be considered.