Characteristics of High-Temperature Titanium Alloy Investment Precision Casting Technology - Metallographic Analysis

At present, research on the long-term use at 600℃ and short-term use above 600℃ of high-temperature titanium alloy investment casting technology is still in its infancy. Compared with ordinary titanium alloys, high-temperature titanium alloy investment casting technology has its own difficulties, mainly including the difficulty in controlling the composition and solidification structure during the melting and casting process due to the large number and high content of alloying elements, the more complex interface interaction between the melt and the surface layer material of the ceramic mold, poor fluidity at normal casting temperatures, and the lack of casting performance parameters.

In view of the characteristics of high-temperature titanium alloy investment casting technology at 600~700℃, this chapter will focus on introducing the interface interaction mechanism between high-temperature titanium alloy melt and oxide ceramic mold, the filling and solidification laws of high-temperature titanium alloy melt under centrifugal force field conditions, the composition control and microstructure properties of high-temperature titanium alloys, and the development of typical high-temperature titanium alloy castings. To ensure uniform composition, unless otherwise specified, the raw materials for casting remelting of high-temperature titanium alloys are all prepared by induction shell melting (ISM) technology.

Interface interaction mechanism between high-temperature titanium alloy melt and oxide ceramic mold
High-temperature titanium alloy melts are highly reactive and react with almost all refractory materials. Therefore, the interface interaction between the alloy melt and refractory materials is a common phenomenon during both melting and casting processes. This interaction can lead to some casting defects, such as surface contamination, porosity, and inclusions of the castings, reducing the quality and performance of the castings. Obtaining the interface interaction laws between high-temperature titanium alloy melts and oxide ceramic molds and revealing the interaction mechanism between the melt and the surface layer of the mold 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 surface layer of the mold
The surface layer refractory material directly contacts the molten titanium alloy, and its own properties have a significant impact on the degree of interface interaction. Currently, oxide refractory materials are widely used in the preparation of investment casting molds for titanium alloys. The standard Gibbs free energy of formation of oxides can be used to compare the relative stability of oxides. The larger the negative value of the Gibbs free energy of formation of the oxide, the more stable the oxide is. However, the standard Gibbs free energy of formation of the oxide does not necessarily correspond completely to the strength of the interface interaction between the oxide refractory material and the titanium alloy melt. The influence of the dissolution of the oxide refractory material must be considered when studying the interface interaction.