Application And Development of Investment Casting Technology in High Temperature Alloy Castings

As an advanced near net forming technology, investment casting is widely used in the precision forming of difficult to machine parts and thin-walled complex components in fields such as aerospace, advanced manufacturing, and medical equipment. It has many advantages such as fast forming of complex castings, fewer processing steps, and high dimensional accuracy. Especially for high-temperature alloys used in aircraft engines, the complex and difficult to machine forming structure of this alloy makes near net forming technology irreplaceable. With the continuous development and progress of investment casting technology, the research and development of new materials, advanced casting processes, and fast forming methods have made investment casting technology develop towards a more precise, lightweight, integrated, and environmentally friendly direction.

In order to meet the positioning goals of high-performance products in response to market and future industrial strategy development, research on ceramic based shells with excellent properties such as high temperature resistance, high strength, and thermal conductivity has become a key direction of research in countries around the world. As a key raw material for investment casting, silica sol has better stability and flowability in the slurry, is easy to store, and has a simple shell making process. It is widely used for directional solidification of high-temperature alloys, casting of single crystal blades, and casting of shell without excess. Due to the poor wettability and long hardening time of silica sol slurry, the wet strength of the shell is low and the residual stress is high. However, there is a mutual constraint between the strength, breathability, and thermal conductivity of silica sol shell. Traditional processes increase the number of shell layers to improve the strength of the shell, but the matrix structure of the shell is denser and the number of internal pores is fewer, resulting in a decrease in the breathability and thermal conductivity of the shell. Polyacrylonitrile (PAN) - based carbon fiber is a filamentous carbon material with excellent burn resistance, high temperature resistance, lightweight, and thermal conductivity. It plays an indispensable role as a key material in the thermal protection system of spacecraft . Therefore, it can be used as a reinforcing material to improve the strength of silica sol shells. Nylon 66 fiber is an organic fiber with excellent physical and chemical properties, making it the best fiber for enhancing resin based composite materials. Due to the tendency of nylon 66 fiber to burn out during calcination, many micro pores are left inside the matrix, which enhance the breathability and thermal conductivity of the shell. Based on the new idea of fiber-reinforced composite materials, hybrid fibers are added as reinforcement to strengthen the silica sol shell, which improves the breathability and thermal conductivity of the shell while ensuring sufficient strength.

This project mainly focuses on the problems of low strength, poor breathability, and thermal conductivity of investment casting shells. By using a hybrid fiber of carbon fiber and nylon 66 to reinforce the silica sol shell, it is expected to improve the breathability and thermal conductivity of the shell while ensuring its strength. Testing and analyzing the influence of carbon fiber and hybrid fiber content on the coating and shell properties of silica sol slurry, exploring the optimal preparation process of fiber-reinforced silica sol shell, aiming to provide theoretical guidance for the preparation of high-quality precision cast shell.