Engineered Matrix Self-Healing Composites
materials and coatings
Engineered Matrix Self-Healing Composites (LEW-TOPS-30)
Innovative approach for improved SiC/SiC ceramic matrix composites
Overview
Nickel-based superalloys have been used in high-temperature, high-stress applications (such as airplane turbine blades and vanes) for years. An increased effort to develop lightweight, high-temperature, creep-resistant substitute materials has led to the formulation and implementation of silicon carbide ceramic matrix composites (SiC/SiC CMCs). In current-generation SiC/SiC composites, the matrix tends to crack prematurely when stresses are applied, thus requiring the SiC fibers to carry almost the entire load. To remedy this deficiency, innovators at NASA's Glenn Research Center have successfully created an engineered matrix composite that offers increased resistance to cracking and "self-heals" the cracks that do occur, by converting oxygen into a low-viscosity oxide that acts as a sealant. This groundbreaking concept provides considerable flexibility in designing the composite matrix for a potentially wide variety of high-temperature applications.
The Technology
When a ceramic matrix cracks, the crack often occurs at the interface between the fibers and the matrix. Glenn scientists have invented a method to fabricate engineered matrix composites (EMCs) using slurry casting and melt infiltration techniques. These EMCs are designed to match the coefficient of thermal expansion (CTE) of the SiC fiber. With this technique, the matrix is better able to withstand loading conditions at high temperatures, and any cracks that develop are prevented from spreading or deepening. This important feature, called "crack tip blunting", should allow the matrix to carry some load before transferring to the reinforcing SiC fibers, thereby increasing the durability of the composite.
The other unique feature of this matrix is its ability to convert ingressed oxygen, which can lead to damaging oxidation of the fibers, to low-viscosity oxides. These oxides spread through capillary action and fill any fine cracks they encounter, thereby "self-healing" and protecting the fibers. The innovators at Glenn also modified the melt infiltration process so less free silicon remains after the process. Typically, the presence of free silicon limits the use of these composites to conditions under 2400°F, but composites made with this engineered matrix are designed to be used at or above 2700°F, further extending the possible properties and applications of this new design.
This is an early-stage technology requiring additional development. Glenn welcomes co-development opportunities.
Benefits
- Efficient: Self-healing enables increased load-carrying capacity and high thermal conductivity
- Reliable: Thermal plasticity helps matrix maintain integrity longer
- Cost-effective: Load-sharing and self-healing extends the life of the composite
- Versatile: Flexible design allows easy adaptation to specific conditions
Applications
- Jet turbine engines
- Land-based power generation
- Nuclear fission and fusion reactors
- Heat exchangers
- Furnace components
