Friction Welding Coarse-Grain PM Superalloys via Local Grain Refinement
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Solution Overview
Problem
Coarse grain nickel-base superalloys used in gas turbine engine components are difficult to weld due to their high flow stress, which makes them challenging to join effectively, especially in high-temperature applications, leading to issues like remnant notch and material degradation during the welding process.
Innovation Solution
The microstructure is altered by local mechanical working and subsequent heat treatment to transform coarse grain to fine grain near the weld surfaces, reducing flow stress and improving weldability through friction welding by achieving compressive residual stress and recrystallization, allowing for bonding at lower temperatures with reduced material degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If coarse grain nickel-base superalloys are used for high-temperature gas turbine components, then strength and creep capability at elevated temperatures are improved, but weldability deteriorates due to high flow stress
Solution Approach 1:
The patent applies local quality by creating a fine grain microstructure specifically at the weld interface and heat affected zone through controlled grain refinement techniques, while maintaining the coarse grain structure in the base material to preserve high-temperature strength. This localized microstructural modification enables weldability improvement without sacrificing the overall strength and creep resistance of the coarse grain superalloy components.
Solution Approach 2:
The patent employs parameter changes by modifying the microstructural parameters (grain size) through controlled thermomechanical processing and heat treatment regimes. By adjusting heating temperature, holding time, and cooling rate during welding and post-weld heat treatment, the patent transforms the coarse grain structure to fine grain structure at the weld zone, reducing flow stress and improving weldability while maintaining the bulk material's high-temperature properties.
2Ease of manufacture
If conventional welding methods are used on coarse grain superalloys, then joining of components is achieved, but material degradation occurs due to high flow stress and remnant notch formation
Solution Approach 1:
The patent applies preliminary action by performing pre-weld heat treatment and controlled grain refinement on the superalloy components before welding. This preliminary processing creates a fine grain microstructure at the weld interface, reduces flow stress, and prevents remnant notch formation during the welding process, thereby avoiding material degradation and ensuring weld joint integrity.
Solution Approach 2:
The patent converts the harmful effect of coarse grain structure (high flow stress, poor weldability) into a benefit by utilizing controlled grain refinement during welding. The high temperature welding process itself is used to transform the coarse grain structure to fine grain structure at the weld zone, which then provides improved weldability and reduced material degradation, turning the original disadvantage into an advantage.
3Ease of manufacture
If welding temperature is increased to join coarse grain superalloys, then bonding is achieved, but defects such as cracks, liquation, and porosity increase
Solution Approach 1:
The patent applies parameter changes by optimizing the welding temperature and heat input parameters to achieve bonding at lower temperatures than conventional methods. By controlling the heating rate, peak temperature, and holding time, the patent prevents excessive grain growth and minimizes the formation of welding defects such as cracks, liquation, and porosity, thereby improving weld joint quality while maintaining welding feasibility.
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 enhances the weldability of coarse grain alloys by reducing flow stress, minimizing defects such as cracks, liquation, and porosity, and improving the quality of weld joints, enabling the use of lower temperatures and energies during welding, thus preventing material degradation and enhancing the structural integrity of the rotor components.
Implementation Method 1
Friction welding a first face of the first PM part to a second face of the second PM part
Implementation Method 2
The microstructure is altered by local mechanical working and subsequent heat treatment to transform coarse grain to fine grain near the weld surfaces
Implementation Method 3
achieving compressive residual stress and recrystallization
Data Source
Figure 1
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AI summary
A method for welding a first powder metallurgical (PM) part to a second powder metallurgical (PM) part includes: working a first face of the first PM part; working a first face of the second PM part; and friction welding the first face of the first part to the first face of the second part.