Rare Earth Silicate Coating with Boron Flux for CMC Crack Prevention
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Solution Overview
Problem
Ceramic matrix composites (CMCs) used in high-temperature and corrosive environments, such as aeronautical turbines, degrade due to oxidation and corrosion, leading to premature failure, and existing environmental barrier coatings often crack during sintering, reducing their gas tightness and effectiveness.
Innovation Solution
A method involving a coating composition with a rare earth silicate and boron powders, where boron acts as a fluxing agent to increase creep and reduce stress, applied in a specific mass ratio of 0.1% to 5% to prevent cracking and enhance the density of the environmental barrier, which is then sintered at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If liquid processing methods (dip-coating) are used to form environmental barriers, then implementation cost is reduced, but the environmental barriers develop cracks during sintering that reduce gas tightness
Solution Approach 1:
The patent changes the chemical composition parameters of the coating by adding boron-containing compounds (such as borax, boric acid, or boron carbide) at specific concentrations (0.1-5 mass%). This compositional parameter change modifies the sintering behavior of the rare earth silicate particles, enabling stress relaxation through enhanced creep mechanisms during sintering, which prevents crack formation while maintaining the low-cost liquid processing method
Solution Approach 2:
Boron-containing compounds act as an intermediary substance that facilitates stress relaxation during sintering. The boron compounds form eutectic phases or liquid bridges between silicate particles at sintering temperatures, enabling plastic deformation and stress accommodation before solidification, thereby preventing crack formation in the final environmental barrier coating
2Reliability
If environmental barriers are formed by sintering rare earth silicate particles, then protective properties are achieved, but stresses during sintering cause cracking that reduces effectiveness
Solution Approach 1:
The patent modifies the chemical composition of the coating by incorporating boron-containing compounds at optimized concentrations. This parameter change enables the material to undergo stress relaxation mechanisms during sintering through enhanced creep behavior, allowing the environmental barrier to maintain integrity and protective properties without cracking
Solution Approach 2:
The boron-containing compounds are distributed throughout the coating composition to create localized regions of enhanced stress relaxation capability. These localized modifications allow different regions of the coating to accommodate stresses differently during sintering, preventing crack propagation while maintaining overall structural integrity and protective function
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 produces a dense and crack-free environmental barrier that effectively protects CMCs from high-temperature corrosion, maintaining mechanical properties and gas tightness even on irregular surfaces, thereby extending the lifespan of CMC components.
Implementation Method 1
Boron is a fluxing agent for silicates and increases the creep of the coating at high temperatures and makes the system viscous in order to accommodate the stresses and prevent cracking
Implementation Method 2
Boron is a fluxing agent for silicates and increases the creep of the coating at high temperatures
Implementation Method 3
sintering the first and second powders in order to obtain the environmental barrier on the part
Data Source
AI summary
A method for coating a ceramic matrix composite part with an environmental barrier, includes a) applying, to the surface of the part, a coating composition including a first powder of a rare earth silicate and a second powder including boron, the coating composition having a ratio R=[mass of the second powder]/[mass of the first powder] of between 0.1% and 5%, wherein the second powder includes a boron powder, and b) sintering the first and second powders in order to obtain the environmental barrier on the part.