The present disclosure relates generally to casting mold compositions, and methods for casting titanium and titanium alloys.
Modern gas turbines, especially aircraft engines, must satisfy the highest demands with respect to reliability, weight, power, economy, and operating service life. In the development of aircraft engines, the material selection, the search for new suitable materials, as well as the search for new production methods, among other things, play an important role in meeting standards and satisfying the demand.
The materials used for aircraft engines or other gas turbines include titanium alloys, nickel alloys (also called super alloys) and high strength steels. Titanium alloys are generally used for compressor parts, nickel alloys are suitable for the hot parts of the aircraft engine, and the high strength steels are used, for example, for compressor housings and turbine housings. The highly loaded or stressed gas turbine components, such as, components for a compressor, for example, are forged parts. Components for a turbine, on the other hand, are typically fabricated as investment cast parts.
Although investment casting is not a new process, the investment casting market continues to grow as the demand for more intricate and complicated parts increase. Because of the great demand for high quality, precision castings, there continuously remains a need to develop new ways to make investment castings more quickly, efficiently, cheaply and of higher quality.
Conventional investment mold compounds that consist of fused silica, cristobalite, gypsum, or the like, that are used in casting jewelry and dental prostheses industries are not suitable for casting reactive alloys, such as titanium alloys. One reason is because there is a reaction between mold titanium and the investment mold. It is difficult to investment cast titanium and titanium alloys and similar reactive metals in ceramic molds because of the titanium's high affinity for elements such as, oxygen, nitrogen, and carbon. At elevated temperatures, titanium and its alloys can react with the mold facecoat.
The properties of the final casting are greatly deteriorated if any reaction occurs between the molten alloy and the mold. The form of this deterioration can include a poor surface finish due to gas bubbles, or in more serious cases, the chemistry, microstructure, and properties of the casting are compromised. Asperities and/or pits on the surfaces of cast alloy components can reduce aerodynamic performance in, for example, turbine blade applications, and increase wear and friction in rotating or reciprocating part applications. Therefore, there is a need in the art for new, practical and useful casting mold compositions and methods for detecting inclusions in reactive alloys, such as titanium alloys.