Single-Crystal Superalloy Sheets from Cast Spiral Workpieces
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Solution Overview
Problem
Current methods for producing large sheets of nickel base superalloy single crystals are limited by furnace size and maintaining thermal gradients during directional solidification, making it challenging to manufacture large single-crystal components like industrial gas turbine blades.
Innovation Solution
A method involving a spiral metallic workpiece with a single crystal structure, characterized by progressively varying crystallographic orientation, is used, where the workpiece is cast and then flattened into a sheet form, allowing for the production of large single-crystal sheets with controlled crystallographic directions and properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If directional solidification of investment cast mold is used to produce large sheets of nickel base superalloy single crystal, then single crystal structure is achieved, but furnace size and withdrawal height are limited
Solution Approach 1:
The casting process is divided into multiple stages: first casting a solidification precursor in a manageable size, then performing a second directional solidification to grow the final large single crystal sheet from the precursor. This segmentation allows the process to bypass furnace size limitations by growing the crystal in stages rather than attempting to form the entire large sheet in one casting operation.
Solution Approach 2:
A solidification precursor is cast and prepared in advance as a foundation for the final single crystal sheet. This preliminary action creates a ready-made substrate with controlled crystal structure that can then be used to grow the final large-area single crystal component, avoiding the need to form the entire structure in a single difficult casting operation.
2Area of stationary object
If the bottom chill plate is withdrawn beyond a certain height, then larger single crystal sheets can be produced, but maintaining thermal gradient becomes technically challenging
Solution Approach 1:
The thermal gradient control problem is segmented into two manageable parts: the first directional solidification creates a solidification precursor with established thermal profile, and the second directional solidification grows the final sheet from this precursor. This avoids the need to maintain thermal gradient over the entire height of a very large single casting, as the process is divided into stages with smaller thermal gradients at each stage.
Solution Approach 2:
The solidification precursor is prepared in advance with controlled crystal orientation and structure. This preliminary structure serves as a template that guides the growth of the final single crystal sheet, ensuring that the thermal gradient and crystal growth proceed in a controlled manner during the second solidification stage, rather than attempting to control the entire growth process from scratch.
3Area of stationary object
If liquid metal cooling is applied to maintain thermal gradient, then larger sheets can be produced, but investment cost increases significantly
Solution Approach 1:
The cooling system requirements are segmented between two casting stages. The first stage produces a solidification precursor using conventional cooling methods. The second stage grows the final sheet from this precursor, requiring less aggressive cooling than would be needed to form the entire large sheet in one operation. This segmentation reduces the need for expensive liquid metal cooling systems while still achieving large-area single crystal production.
Solution Approach 2:
The solidification precursor is created in advance using cost-effective conventional cooling methods. This precursor then serves as the foundation for the second growth stage, reducing the thermal management requirements compared to attempting to form the entire large single crystal sheet in one expensive, complex casting operation requiring liquid metal cooling.
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
This approach enables the production of large single-crystal sheets with varying Young's modulus and crystallographic properties, suitable for structural applications, while maintaining cost-effectiveness and expanding design options for components like turbine blades and honeycombs.
Implementation Method 1
directional solidification of an investment cast mold
Data Source
Figure 1
Figure 2
Figure 2A
AI summary
A method comprises: providing a spiral metallic workpiece (20;200) having a cast structure associated with such spiral; and at least partially flattening the workpiece.