Turbine Airfoil Section Replacement Below Grain Boundary Temperature
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Solution Overview
Problem
Superalloy components, such as turbine blades, face degradation during gas turbine engine operation, leading to costly replacements, and traditional welding processes can cause cracking due to grain boundary melting, especially in nickel-based superalloys.
Innovation Solution
A method using a presintered preform made of a powder mixture of superalloy particles and braze material is inserted between the airfoil and replacement sections, and the assembly is resistance brazed at a temperature below the grain boundary melting point, using high melting point braze materials like Ni—Cr—Ti, Ni—Cr—Zr, or Ni—Cr—Hf to prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional welding processes are used to join superalloy components, then the components can be joined together, but grain boundary melting occurs causing cracks in the material
Solution Approach 1:
A presintered preform composed of superalloy particles and braze material acts as an intermediary between the two superalloy components. The preform enables joining through resistance brazing at temperatures below the grain boundary melting point of the base superalloy, preventing cracks while achieving strong joints. The braze material in the preform melts and flows to create the bond without exposing the base metal to damaging temperatures.
Solution Approach 2:
The invention changes the temperature parameter of the joining process by using resistance brazing instead of welding. The process operates at a controlled temperature range that melts the braze material (which has a lower melting point) while keeping the base superalloy below its grain boundary melting temperature, thus preventing thermal damage while achieving metallurgical bonding.
2Reliability
If low temperature brazing is used to prevent grain boundary melting, then cracking is avoided, but the melting temperature of the braze material must be carefully controlled below the grain boundary temperature
Solution Approach 1:
The presintered preform is prepared in advance with a specific composition of superalloy particles and braze material in predetermined ratios. This preliminary preparation ensures that during the resistance brazing process, the temperature naturally self-regulates to melt the braze material while keeping the base superalloy below its grain boundary melting point, eliminating the need for complex temperature control systems.
3Reliability
If a presintered preform with braze material is used for resistance brazing, then joining is achieved without grain boundary melting, but the preform must be precisely configured to mate with both airfoil surfaces
Solution Approach 1:
The presintered preform is segmented into distinct components: superalloy particles providing structural compatibility and braze material providing bonding capability. This segmentation allows each component to perform its specific function - the superalloy particles maintain dimensional stability and compatibility with the base metal, while the braze material melts and flows to create the joint, simplifying the overall configuration requirements.
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 effectively joins superalloy components without grain boundary melting, reducing the risk of cracking and maintaining the structural integrity of the repaired airfoil, allowing for the use of high-temperature braze materials that achieve near-base-metal fatigue properties.
Implementation Method 1
The stacked airfoil is resistance brazed such that only the braze material of the presintered preform melts and the upper surface of the airfoil and the lower surface of the replacement section remain below the grain boundary temperature of a material of the airfoil
Implementation Method 2
only the braze material of the presintered preform melts
Data Source
AI summary
A method of repairing an airfoil is provided. The method includes providing an airfoil with a damaged section and removing the damaged section by machining or cutting an upper section of the airfoil. A replacement section is configured to mate with an upper surface of the airfoil. A presintered preform is provided to join the airfoil and the replacement sections through a resistance brazing process. The presintered preform is configured to mate with the upper surface of the airfoil and a lower surface of the replacement section and inserted between this upper surface and lower surface, creating a stacked airfoil comprising three mated sections in abutting contact. The stacked airfoil is resistance brazed such that only the braze material of the presintered preform melts and the upper surface of the airfoil and the lower surface of the replacement section remain below the grain boundary temperature of the material of the airfoil.