High Thermal Conductivity Shell Mold for Directional Solidification
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Solution Overview
Problem
Conventional shell molds for directional solidification of superalloys and transition metal-based alloys have limited heat extraction due to low thermal conductivity and thickness, hindering the achievement of high thermal gradients necessary for improved mechanical properties in turbine components.
Innovation Solution
The development of high thermal conductivity shell molds with a facecoat, sealcoat, and support structure, where the support includes a high thermal conductivity stucco material like silicon carbide in excess of 50 volume percent, and a median size greater than 100 microns, allowing for a thinner shell thickness of less than 7 mm, thereby enhancing heat extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional shell molds made of alumina or zircon particulates are used, then the mold structure is simple and easy to manufacture, but the thermal conductivity is low (1.42-1.62 W/m-K) resulting in limited heat extraction rate
Solution Approach 1:
The shell mold uses a composite material system combining high thermal conductivity stucco (silicon carbide, aluminum nitride, or diamond) with refractory ceramic binders. The stucco concentration is optimized at 40-60 volume percent to achieve thermal conductivity greater than 2.0 W/m-K while maintaining structural integrity and manufacturability through conventional shell mold fabrication processes
Solution Approach 2:
The invention changes the thermal conductivity parameter of the shell mold material from conventional values (1.42-1.62 W/m-K) to enhanced values (>2.0 W/m-K) by selecting stucco materials with inherently higher thermal conductivity such as silicon carbide, aluminum nitride, or diamond, while adjusting stucco concentration and particle size distribution to optimize both heat extraction and manufacturability
2Loss of energy
If shell thickness is increased to improve heat extraction, then heat extraction rate increases, but the mold becomes thicker and more complex
Solution Approach 1:
The invention changes the material parameter (thermal conductivity) to compensate for reduced thickness. By using stucco materials with thermal conductivity >285 W/m-K (such as diamond or aluminum nitride) at 40-60 volume percent concentration, the shell achieves enhanced heat extraction rate with reduced thickness of 5-10 mm, eliminating the need for increased thickness to achieve the same heat extraction performance
3Temperature
If high thermal conductivity stucco material is used in the support, then thermal conductivity increases to greater than 2.0 W/m-K, but the support composition becomes more complex
Solution Approach 1:
The support uses a composite formulation of high thermal conductivity stucco particles (silicon carbide, aluminum nitride, or diamond) dispersed in a refractory ceramic binder matrix. The stucco concentration is optimized at 40-60 volume percent to achieve thermal conductivity >2.0 W/m-K while maintaining compatibility with conventional shell mold fabrication processes, ensuring the composition remains manufacturable despite the enhanced material requirements
Solution Approach 2:
The invention applies local quality by concentrating high thermal conductivity stucco material specifically in the support layer between the facecoat and sealcoat, where maximum heat extraction benefit is needed. The facecoat and sealcoat maintain conventional compositions for their specific functions (surface finish and release properties), while the support is optimized for thermal conductivity, creating a functionally graded structure
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 high thermal conductivity shell molds significantly increase heat extraction rates, leading to improved mechanical properties such as increased coercivity, remanence, and energy product in cast components, and enable faster casting processes with refined microstructures and higher product yield.
Implementation Method 1
Heat extraction from solidifying casting in Liquid Metal Cooling (LMC) directional solidification is limited by shell heat conduction when the conventional shell molds are applied
Implementation Method 2
The sealcoat is disposed on an outer surface of the shell mold and includes a high emissivity material
Data Source
AI summary
A shell mold is described. The shell mold includes a facecoat, a sealcoat, and a support disposed in between the facecoat and the sealcoat. The support includes a stucco in a concentration greater than about 40 volume percent of the support. The stucco includes a material that has a thermal conductivity greater than about 285 W/m-K.