Composite core for casting processes, and processes of making and using the same

Abstract

A composite ceramic core that, in combination with a shell mold, is suitable for use in a casting process to produce metal alloy components. The core and casting process make use of a highly leachable interior layer in combination with an exterior layer that is less reactive than the interior layer in the presence of common alloying elements. The interior layer contains at least one hollow channel that allows a point of entry for a leaching solution, as well as exit for gaseous byproducts generated during the casting process.

Description

BACKGROUND OF THE INVENTION[0001]The present invention generally relates to casting processes and materials. More particularly, this invention relates to cores and processes for casting reactive metal alloys, such as a steels (including stainless steels), superalloys, titanium-base alloys, etc.[0002]Metal alloy materials can be formed into components by various casting techniques, a notable example being investment casting (lost wax) processes. Investment casting typically entails dipping a wax or plastic model or pattern of the desired component into a slurry comprising a binder and a refractory particulate material to form a slurry layer on the pattern. A common material for the binder is a silica-based material, for example, colloidal silica. A stucco coating of a refractory particulate material is typically applied to the surface of the slurry layer, after which the slurry / stucco coating is dried. The preceding steps may be repeated any number of times to form a shell mold of su...

AI Technical Summary

Benefits of technology

The invention allows the core to leach out of the casting quickly while reducing the chance of reaction with the metal alloy. It also prevents gas from entering the casting, reducing defects in the component.

Problems solved by technology

Additional challenges are encountered when attempting to form hollow castings of reactive materials, including stainless steel alloys, as a result of their reactivity.

However, silica devitrifies at high temperatures (e.g., about 1200° C.) causing the core to gradually lose strength and distort during a casting process.

Silica also reacts with alloying elements, such as Al, Ni, Cr, Y, Zr, etc., which may cause surface depletion zones, internal oxidation and other deleterious effects.

For example, oxidation and loss of aluminum, nickel, chromium, yttrium and / or zirconium may cause rejection of an expensive casting.

In addition, a product of the oxidation reaction is SiO, which is gaseous at pour temperature and can become trapped in a casting to form gas defects.

Also, the reaction may cause a core body and the metal casting to tightly stick to each other, with the result that the core is more difficult to remove.

However, alumina cores tend to have a very low leach rate, implying that a much longer leach operation is needed to completely remove the core body from a solidified article.

Due to the longer leach operations, the leach agent may attack the metal casting and form reaction pits.

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