Mold Surface Modifications for Thermal Gradient Control in Single Crystal Casting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The directional solidification process for casting single crystal components, such as turbine blades, faces challenges in maintaining a stable temperature gradient across the liquid/solid interface, particularly in areas with varying cross-sectional areas, leading to defects like freckling and secondary grains due to heat radiation variations and convective instabilities.
Innovation Solution
A mould design with recesses or projections that increase the surface area of the mould portion, enhancing radiative heat loss and controlling the thermal gradient during the directional solidification process, thereby reducing defects in the single crystal structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If directional solidification is used to achieve single crystal structure, then creep resistance and high temperature performance are improved, but defects like freckling and secondary grains occur in components with varying cross-sectional area
Solution Approach 1:
The invention applies different surface characteristics to different regions of the mould. Specifically, the downward-facing surfaces in the heating zone are given a high emissivity coating to maximize radiative heat loss locally, while other regions maintain standard conditions. This localized modification of heat transfer properties addresses the specific problem of thermal instability in varying cross-sectional areas without altering the entire mould system.
Solution Approach 2:
The invention changes the radiative heat transfer parameter by applying a high emissivity coating to the mould's downward-facing surfaces. This parameter change increases the radiative heat loss from these surfaces, thereby stabilizing the temperature gradient in the mushy zone and preventing convective instabilities that cause defects in components with varying cross-sections.
2Temperature
If radiation deflector element is used to reduce heat transfer between downward facing surfaces and chill plate, then temperature gradient control is improved, but device complexity increases
Solution Approach 1:
The invention converts the potentially harmful direct radiative heat transfer from downward-facing surfaces to the chill plate into a beneficial process by applying high emissivity coatings. This increases the desired radiative heat loss from these surfaces to the molten metal, stabilizing the temperature gradient without requiring mechanical barriers or deflectors that would add complexity to the mould 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 increased radiative heat loss from the mould portion helps in maintaining a stable thermal gradient, minimizing defects in the single crystal structure and improving the quality of the cast components.
Implementation Method 1
increasing radiative heat loss from said at least one mould portion during said process
Data Source
AI summary
A method includes forming a mold, the mold having at least one mold portion defining the shape of an element to be removed from the component in a subsequent manufacturing step and having a reduced cross-sectional area. The at least one mold portion includes at least one recess which further reduces the cross sectional area of the cavity and increases the surface area of the at least one mold portion or the at least one mold portion includes a plurality of projections which increase the surface area of the least one mold portion thereby increasing radiative heat loss from the at least one mold portion during the process. A mold for use in this method and a turbine blade formed using this method, are also provided.