Oxidation Resistant Coating Slurry Process for Turbine Engines
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Solution Overview
Problem
Current oxidation protection coatings for advanced turbine and hypersonic engines face challenges in providing stable, high-temperature oxidation resistance while maintaining mechanical strength, as they either lack sufficient protection above 1650°C or compromise substrate strength.
Innovation Solution
A process involving a slurry of silica-based materials with specific particle sizes and viscosities, combined with oxygen scavengers like molybdenum, tantalum, or chromium silicides/borides, applied to silicon-containing materials and heat-treated under an inert atmosphere to form a glassy phase that actively reacts with oxygen, rebuilding the coating and accommodating thermal expansion mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silica-based high melting point glasses are used for oxidation protective coatings, then oxidation resistance is improved, but protection is not effective in the range of 650°C to 1650°C
Solution Approach 1:
The invention changes the chemical composition parameters of the glassy coating material by incorporating specific ratios of silica (40-70 wt%), alumina (10-30 wt%), and magnesia (5-20 wt%), along with controlled amounts of soda oxide and potash oxide. This compositional adjustment allows the coating to maintain structural stability and oxidation resistance across the extended temperature range of 650°C to 1650°C, overcoming the limitation of conventional silica-based coatings that fail above 1650°C
Solution Approach 2:
The invention creates a composite glassy coating system by combining multiple oxide components (silica, alumina, magnesia, soda oxide, potash oxide) into a synergistic formulation. This composite approach allows the coating to exhibit both low-temperature stability (preventing spallation and cracking) and high-temperature oxidation resistance, effectively bridging the performance gap between 650°C and 1650°C operating conditions
2Reliability
If refractory metal silicide coatings are formed by high temperature annealing, then oxidation resistance is improved, but complex scales form involving silica, metal silicates and metal oxides that exacerbate thermal expansion problems
Solution Approach 1:
The invention changes the chemical formulation parameters by using a carefully balanced glassy matrix containing silica, alumina, and magnesia in specific proportions, with controlled additions of volatile oxides. This compositional design allows the coating to form a stable, homogeneous structure that resists phase separation and complex scale formation, maintaining composition stability across thermal cycling while providing effective oxidation protection
Solution Approach 2:
The glassy coating acts as an intermediary layer between the substrate and the oxidizing environment. This intermediate structure provides a stable, protective barrier that prevents direct interaction between the substrate and aggressive oxidizing conditions, thereby avoiding the formation of complex, unstable scales while maintaining both oxidation resistance and compositional stability
3Reliability
If commercially available coatings are applied to C/SiC substrates, then oxidation protection up to 1650°C is achieved, but the strength of the underlying substrate is significantly decreased
Solution Approach 1:
The invention adjusts the coating composition parameters to create a glassy matrix with optimized viscosity and thermal expansion characteristics. By controlling the ratios of silica, alumina, magnesia, and volatile oxides, the coating achieves both superior oxidation protection and enhanced substrate strength retention, overcoming the trade-off where conventional coatings provide protection but compromise mechanical properties
Solution Approach 2:
The invention develops a composite glassy coating system that combines multiple oxide phases with complementary properties. This composite structure provides both oxidation resistance and mechanical reinforcement to the substrate, eliminating the need to sacrifice substrate strength for protection while maintaining integrity at temperatures up to 1650°C
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 solution provides enhanced oxidation resistance up to 3000°F, reducing spallation and cracking, and offering improved mechanical properties, with coated substrates showing 5 to 9 times better protection than uncoated ones, while also addressing steam resistance and thermal expansion issues.
Implementation Method 1
a glassy phase that actively reacts with oxygen, rebuilding the coating
Implementation Method 2
accommodating thermal expansion mismatches
Data Source
Figure 1
Figure 2~3
AI summary
A process for applying an oxidation resistant coating (24) to an article (20) includes the steps of mixing (10) at least about 10% by volume to up to about 99% by volume of a slurry at least one silica based material having a viscosity of about 1x102 poise to about 1x107 poise at a temperature of about 1,292°F (700°C) to about 3,272°F (1,800°C) at least about 1% by volume to up to about 90% by volume of the slurry at least one oxygen scavenger, and a liquid medium to form the slurry; coating (12) an article (20) with the slurry to form a slurry coated article; and heat treating (16) under an inert atmosphere the slurry coated article to form an article having at least one oxidation resistant coating layer (24) containing the at least one oxygen scavenger.