Rare Earth Core for Refractory Casting Dimensional Stability
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Solution Overview
Problem
Ceramic cores used in casting high-temperature materials like refractory metal intermetallic composites face challenges in achieving dimensional stability, strength, low crush strength, leachability, and chemical inertness, making it difficult to produce high-quality castings with minimal defects.
Innovation Solution
A method involving the formation of a porous core body with a binder and at least 50% rare earth metal oxide, followed by heating to remove the binder and infiltrating with metal oxide particles, then heat-treating to sinter without significant dimensional change, creating a core with enhanced strength and stability for casting RMIC materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional ceramic cores are fired at elevated temperatures to remove binder and strengthen the core, then the core strength is improved, but the core exhibits excessive shrinkage greater than 0.2%
Solution Approach 1:
The patent changes the chemical composition parameters of the core material by incorporating rare earth metal oxides (at least 50% by weight) and specific ceramic materials. This compositional parameter change allows the core to maintain dimensional stability during firing while achieving the required strength, resolving the contradiction between strength improvement and dimensional accuracy preservation.
Solution Approach 2:
The patent uses composite ceramic materials comprising rare earth metal oxides combined with other ceramic materials such as silica, alumina, and zirconia. This composite structure provides both the strength needed to withstand casting temperatures and the dimensional stability required to minimize shrinkage, simultaneously addressing both requirements.
2Ease of operation
If the core porosity is increased to facilitate easy removal and reduce crush strength, then the core removal ease is improved, but the core strength is reduced
Solution Approach 1:
The patent applies local quality by creating different regions within the core with different porosity characteristics. The core has controlled porosity distribution that facilitates removal in specific areas while maintaining sufficient strength in load-bearing regions. The rare earth metal oxide composition enables this differentiated structure to achieve both ease of removal and adequate strength.
3Reliability
If the core is made chemically inert to prevent reaction with RMIC materials, then the casting quality is improved, but the core material selection is limited
Solution Approach 1:
The patent achieves universality by developing a core material composition (rare earth metal oxides combined with various ceramic materials) that can serve multiple functions simultaneously: providing chemical inertness to prevent reactions with RMIC materials, maintaining dimensional stability during firing, achieving sufficient strength, and enabling easy removal. This multi-functional composition resolves the contradiction between casting quality and material selection flexibility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method produces cores that maintain dimensional accuracy, provide sufficient strength, facilitate easy removal, and exhibit chemical inertness, enabling the successful casting of high-quality RMIC components with reduced defects.
Implementation Method 1
heating the core body under heating conditions sufficient to remove a substantial portion of the binder
Implementation Method 2
infiltrating the core body with a liquid colloid or solution which comprises particles of at least one metal oxide compound
Implementation Method 3
heat-treating the particle-infiltrated core body under heating conditions sufficient to sinter the particles without substantially changing the dimensions of the core body
Data Source
AI summary
A method of fabricating a core for a ceramic shell mold is disclosed. A porous core body is formed from at least about 50% by weight of at least one rare earth metal oxide. The core body is heated under heating conditions sufficient to provide the core with a density of about 35% to about 80% of its theoretical density. The core body is then infiltrated with a liquid colloid or solution of at least one metal oxide compound, e.g., rare earth metal oxides; silica, aluminum oxide, transition metal oxides, and combinations thereof. The infiltrated core body is then heated to sinter the particles without substantially changing the dimensions of the core body. Mold-core assemblies which include such a core body are also described. A description of processes for casting a turbine component, using the core, is also set forth herein.