Ni Alloy Casting Grain Structure Control via Drawing Speed
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Solution Overview
Problem
The existing methods for manufacturing Ni alloy castings with columnar and equiaxed grain structures require multiple casting steps, leading to decreased productivity due to complexity and increased processing time.
Innovation Solution
A method involving a casting step where molten Ni alloy is poured into a mold on a water-cooling chill plate, with controlled drawing speeds and temperature gradients to form columnar grains, followed by a continuous increase in drawing speed to form equiaxed grains, utilizing a grain refined layer containing cobalt compounds in the mold to refine the grain structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If multiple casting steps are used to form columnar and equiaxed grain structures separately, then the strength characteristics of the Ni alloy casting are improved, but the productivity and manufacturing efficiency deteriorate due to increased process complexity and time
Solution Approach 1:
The patent combines the formation of columnar and equiaxed grain structures into a single continuous casting process. By controlling the drawing speed of the mold through different zones (slow drawing speed of 100-400 mm/hour in the first zone for columnar grains, fast drawing speed of 1000 mm/minute or more in the second zone for equiaxed grains), both grain structures are formed sequentially in one casting step, eliminating the need for separate casting operations and thereby improving productivity while maintaining strength characteristics
Solution Approach 2:
The patent employs dynamic control of the mold drawing speed during the casting process. The drawing speed is varied continuously: initially maintained at a slow rate (100-400 mm/hour) to promote columnar grain formation, then increased to a fast rate (1000 mm/minute or more) to promote equiaxed grain formation. This dynamic adjustment of process parameters within a single casting operation enables the formation of different grain structures at different stages, resolving the contradiction between strength requirements and productivity
2Strength
If multiple casting steps are implemented to create different grain structures in different portions, then the fatigue strength and creep strength are optimized, but the manufacturing complexity and processing time increase
Solution Approach 1:
The patent segments the single casting process into two functional zones along the casting direction: a first zone for forming columnar grains (providing creep strength) and a second zone for forming equiaxed grains (providing fatigue strength). This segmentation is achieved by dividing the casting process into stages with different drawing speeds, allowing each portion of the casting to develop the appropriate grain structure for its functional requirements while maintaining a unified manufacturing process
Solution Approach 2:
The patent utilizes parameter changes, specifically the drawing speed of the mold, to control grain structure formation. By changing the drawing speed from slow (100-400 mm/hour) in the first zone to fast (1000 mm/minute or more) in the second zone, the process transitions from forming columnar grains to forming equiaxed grains. This parameter-based control simplifies the manufacturing process compared to multiple separate casting steps, as it uses a single controllable parameter (drawing speed) to achieve different microstructural outcomes
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 allows for the continuous formation of columnar and equiaxed grains, simplifying the casting process and improving productivity by reducing the number of necessary steps and maintaining excellent strength characteristics in the resulting Ni alloy casting, such as turbine blades.
Implementation Method 1
casting molten Ni alloy by pouring the molten Ni alloy into a cavity of a mold placed on a water-cooling chill plate
Implementation Method 2
forming columnar grain by solidifying the molten Ni alloy while drawing the mold with a temperature gradient provided to a solid-liquid interface
Implementation Method 3
the mold includes a grain refined layer in a cavity-side portion of the mold, the grain refined layer containing a grain refining agent of a cobalt compound
Data Source
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AI summary
A method of manufacturing a Ni alloy casting, includes a casting step (S10) of casting molten Ni alloy by pouring the molten Ni alloy into a cavity of a mold, a columnar grain forming step (S12) of forming columnar grain by solidifying the molten Ni alloy while drawing the mold, in which the molten Ni alloy has been poured, at a drawing speed of 100 mm/hour or more but 400 mm/hour or less with a temperature gradient provided to a solid-liquid interface, and an equiaxed grain forming step (S14) of forming equiaxed grain by solidifying the molten Ni alloy while drawing the mold at a drawing speed of 1000 mm/minute or more continuously after the columnar grain forming step.