Ceramic Matrix Composites (CMCs)

Plane ascending into the sunset thanks to its ceramic matric composites (CMCs) construction.

The word ceramics often summons visions of cups, plates, or pots molded into a shape then fired at a high temperature to harden. Perhaps it is time we start thinking about a different kind of ceramic. Ceramic matrix composites (CMCs) aren’t as instantly recognizable in name as the umbrella term of ceramics, but the related material is just as fascinating.

CMCs are regarded as a subgroup of both composite materials and ceramics. “Ceramic matrix composites combine a ceramic fiber embedded in a ceramic matrix to produce a finished CMC part.” CMC material is lightweight while still maintaining an important durability for the process it is often used for. The material has so much potential for use that the US Department of Energy started a program to support the development of CMCs over 25 years ago.

This versatile material is particularly useful in aviation. General Electric Aviation recently opened a factory in Alabama that will produce this material. CMCs are even catching the attention of NASA for their properties that could potentially help withstand greater amounts of heat than the metal materials currently being used. According to NASA, CMCs “can withstand temperatures up to 2700˚ F and beyond with the help of specially designed ceramic coatings called environmental barrier coatings.” An engine is more efficient when it is hotter.

The first engine to commonly use CMC material is called LEAP. In this engine, there is a CMC component, “a turbine shroud lining its hottest zone.” The LEAP engine started use in 2016. From there, the engines, using the CMC material, have continued to be manufactured and used.

Plane gliding through the sky thanks to its CMC material.

As with all scientific breakthroughs, safety should be considered when the object in question is employed. There are a number of safety standards regarding ceramic matrix composites. For example, ISO 18608:2017: Fine Ceramics (Advanced Ceramics, Advanced Technical Ceramics) – Mechanical Properties Of Ceramic Composites At Ambient Temperature In Air Atmospheric Pressure – Determination Of The Resistance To Crack Propagation By Notch Sensitivity Testing describes a method for the classification of ceramic matrix composite (CMC) materials with respect to their sensitivity to crack propagation using tensile tests on notched specimens with different notch depths.

ASTM C1525-18 Standard Test Method For Determination of Thermal Shock Resistance For Advanced Ceramics By Water Quenching is mostly for dense monolithic ceramics, but is also usable for particulate-reinforced ceramic matrix composites that are macroscopically homogeneous.

There are more standards on ceramic matrix composites from ASTM as well as ISO.

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