Characteristics of high temperature titanium alloy investment precision casting technology - Metallographic analysi

At present, the research on high temperature titanium alloy investment casting technology for long-term use at 600℃ and short-term use above 600℃ is still in its infancy. Compared with ordinary titanium alloy, high temperature titanium alloy investment casting technology has its own difficulties, mainly including more alloying elements and high content of the composition and solidification structure control during the melting process is difficult, melt and ceramic shell material interface interaction is more complex, poor flow performance under normal casting temperature, casting performance parameters lack.

According to the characteristics of 600-700 ℃ high temperature titanium alloy investment casting technology, this chapter will focus on the interaction mechanism between high temperature titanium alloy melt and oxide ceramic shell, the filling and solidification rule of high temperature titanium alloy melt under centrifugal force field, the composition control and microstructure properties of high temperature titanium alloy and the development of typical high temperature titanium alloy castings. In order to ensure uniform composition, except for special instructions, the high temperature titanium alloy raw materials used for casting remelting are prepared by induction shell melting (ISM) technology.

Mechanism of interface interaction between high temperature titanium alloy melt and oxide ceramic shell The titanium alloy melt at high temperature is very active and reacts with almost all the refractories, so the interface interaction between the alloy melt and the refractories is a common phenomenon whether in the melting or pouring process. This effect will lead to the production of some casting defects, such as casting surface pollution, porosity and inclusion defects, reducing the quality and performance of the casting. The interface interaction between high temperature titanium alloy melt and oxide ceramic shell is obtained, and the interaction mechanism between melt and shell is revealed, which is of great significance for the development or production of high quality complex thin-wall high temperature titanium alloy castings.

The interaction between melt and shell layer
The surface refractory is directly in contact with molten titanium alloy, and its own properties have a great influence on the degree of interface interaction. At present, oxide refractories are widely used in the preparation of titanium alloy investment mold precision casting shell. The standard Gibbs free energy of the oxide can be used to compare the relative stability of the oxide, and the greater the negative Gibbs free energy of the reaction to generate the oxide, the more stable the resulting oxide is, while titanium is oxidized to Ti0. The standard Gibbs free energy of oxide formation may not correspond to the interfacial interaction between oxide refractories and titanium alloy melt. The influence of oxide refractories dissolution must be considered when studying the interfacial interaction.