Low Stress Metallic Coating via Bimodal Eutectic Powder
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Solution Overview
Problem
Conventional coating techniques for gas turbine engine components result in excessive tensile stresses, leading to cracking, delamination, and reduced durability due to high kinetic energy deposition and mismatched thermal expansion, causing bond strength loss and component distortion.
Innovation Solution
A method involving a eutectic aluminum-silicon matrix powder with a bimodal particle size distribution and controlled molten fraction, combined with a filler material, is sprayed onto the component at a balanced thermal and kinetic energy to minimize tensile stress, using a Progressive Technologies 100HE torch for optimal velocity and heat input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional plasma spray or HVOF techniques are used to apply thick coatings, then deposition efficiency and coating thickness are improved, but excessive tensile and compressive stresses develop leading to cracking and delamination
Solution Approach 1:
The patent changes the particle temperature parameter during deposition, maintaining particles at or near melting point temperature rather than excessive temperatures. This temperature control reduces thermal stress and prevents cracking while maintaining deposition efficiency
Solution Approach 2:
The patent uses a composite powder mixture containing aluminum, silicon, and methyl methacrylate in specific ratios. This composite material composition creates a coating with balanced thermal and mechanical properties that reduces stress accumulation and improves durability
2Strength
If high kinetic energy is used to deposit powder particles, then coating adhesion is improved, but excessive tensile stress accumulates causing bond strength loss and cracking
Solution Approach 1:
The patent optimizes the kinetic energy parameter by controlling particle velocity and mass, achieving sufficient adhesion without excessive energy input. The bimodal particle size distribution helps balance kinetic energy delivery with stress reduction
Solution Approach 2:
The composite powder formulation with aluminum, silicon, and methyl methacrylate creates a coating that bonds effectively at moderate kinetic energy levels, reducing tensile stress accumulation while maintaining strong adhesion
3Reliability
If coating thickness is increased beyond optimal levels, then protection capability is improved, but tensile stress accumulation increases leading to spontaneous delamination
Solution Approach 1:
The patent controls the deposition parameters including particle temperature, velocity, and molten fraction to reduce tensile stress per layer. This allows building thicker coatings by depositing multiple layers without stress accumulation reaching delamination levels
Solution Approach 2:
The composite coating material with specific aluminum-silicon-methyl methacrylate ratios provides inherent stress management properties, enabling thicker coating applications while maintaining integrity and preventing spontaneous delamination
4Productivity
If standard plasma spray torches are used for maximum particle heating, then deposition efficiency is improved, but component distortion occurs due to excessive thermal input
Solution Approach 1:
The patent modifies the thermal parameters by controlling particle temperature to be at or near melting point rather than excessively high. This reduces heat input to the substrate, preventing thermal distortion while maintaining efficient deposition
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 method achieves a 43% reduction in deflection rate and ensures minimal tensile or compressive stresses in the coating, enhancing bond strength and durability by matching thermal expansion coefficients and balancing energy inputs during deposition.
Implementation Method 1
heating a eutectic aluminum-silicon matrix power to about its melting temperature, the powder having an 88/12 weight percent ratio and a bimodal particle size distribution... wherein the matrix powder has a molten fraction of between about 33% and about 90% by volume at about a melting temperature of the matrix material
Implementation Method 2
spraying the matrix powder at the surface at a velocity sufficient to adhere the matrix powder to the surface... spraying a filler material in powder form at the surface at a velocity sufficient to adhere the filler material to the surface
Implementation Method 3
forming a spray coating material that contains fully molten and partially molten matrix powder and filter material powder during deposition that forms a metal matrix composite when deposited
Data Source
Figure 1~2
AI summary
A composition for deposition as a coating includes a matrix material having a molten fraction of between about 33% and about 90% by volume and a filler material interspersed within the matrix.