Multilayer Coating Architecture for Gas Turbine Aerofoil Oxidation Resistance
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Solution Overview
Problem
Existing coatings for gas turbine aerofoils are brittle and provide limited oxidation protection and temperature durability, often leading to surface cracking due to thermal expansion mismatches and diffusion of corrosive species.
Innovation Solution
A multilayer coating architecture using high power impulse magnetron sputtering (HIPIMS) with alternating layers of silicon and boron-containing metallic nitrides, such as TiAlSiN and CrAlBYN, to form a dense oxide scale that inhibits oxidation and corrosion, and stabilizes the oxide scale to prevent spalling, with bilayer thicknesses in the range of 1 to 20 nm, particularly 2 to 5 nm, to exploit the superlattice effect and enhance toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating is applied to protect against oxidation and corrosion, then oxidation resistance is improved, but the coating itself becomes brittle and cracks under high temperature
Solution Approach 1:
The patent applies composite materials by creating a multilayer coating structure with alternating layers of different compositions (e.g., CrAlSiYN and CrN layers). Each layer provides different functional properties, with some layers optimized for oxidation resistance and others for toughness and crack prevention. This composite structure allows the coating system to simultaneously achieve both oxidation protection and mechanical durability under thermal cycling conditions.
Solution Approach 2:
The coating is segmented into multiple thin alternating layers with bilayer thicknesses in the range of 1 to 20 nm (particularly 2 to 5 nm). This segmentation creates numerous interfaces that act as barriers to crack propagation and allow for differential thermal expansion, preventing the brittle cracking that occurs in single-layer coatings while maintaining oxidation resistance.
2Reliability
If a coating is applied to prevent corrosive species diffusion, then protection is improved, but the coating only provides limited temperature durability
Solution Approach 1:
The patent utilizes parameter changes by carefully controlling the thickness of alternating layers (1-20 nm range) and adjusting the composition ratios of elements such as Cr, Al, Si, Y, and N. These parameter optimizations enable the coating to maintain its protective function at temperatures up to 1100°C or higher, significantly improving temperature durability while preserving corrosion protection capabilities.
Solution Approach 2:
The multilayer composite structure with alternating compositions provides both corrosion protection and high temperature durability. The specific combination of layers (e.g., CrAlSiYN/CrN) creates a system where one layer forms a protective oxide scale while the other provides structural stability and crack resistance, enabling sustained performance in high temperature corrosive environments.
3Reliability
If alternating layers of silicon and boron-containing metallic nitrides are used, then oxidation resistance and cracking protection are improved, but coating complexity increases
Solution Approach 1:
The coating architecture is segmented into alternating layers of silicon-containing nitrides (e.g., TiAlSiN) and boron-containing nitrides (e.g., CrAlBYN) with bilayer thicknesses of 1-20 nm. This segmentation creates a regular, repeating pattern that, while structurally complex, follows a systematic design that can be efficiently deposited using HIPIMS technology. The alternating Si and B layers provide complementary protection: Si forms protective oxide scales while B enhances toughness and reduces cracking.
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 coatings significantly improve oxidation resistance and cracking protection, reducing mass gain during high-temperature exposure and preventing substrate oxidation, as demonstrated by thermo-gravimetric tests, with improved physical properties and reduced fatigue due to the sharp, flat interfaces and specific elemental compositions.
Implementation Method 1
coatings can be applied to the part to be protected by physical vapour deposition (PVD) methods
Implementation Method 2
High power impulse magnetron sputtering (HIPIMS) is a known PVD technique
Implementation Method 3
the alternating layers...form a dense oxide scale that inhibits oxidation and corrosion
Implementation Method 4
The provision of the alternating layers comprising Si and B is believed to inhibit the fast diffusion of oxygen along grain boundaries
Implementation Method 5
surface cracking has been observed to occur during exposure to high temperatures
Implementation Method 6
with bilayer thicknesses in the range of 1 to 20 nm, particularly 2 to 5 nm, to exploit the superlattice effect and enhance toughness
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A coated substrate comprising a metal or metal alloy such as a high speed steel, TiAl based alloy or Ni based alloy or an electrically conductive ceramic material, wherein the coating comprises a hard material protective coating comprising alternating layers of different compositions, wherein a first composition of the alternating layers comprises silicon, Si, and/or a second composition of the alternating layers comprises boron, B.