Published on May 20th, 2014 | By: firstname.lastname@example.org
Ceramics & the MilitaryPublished on May 20th, 2014 | By: email@example.com
[Image above] Credit: Public Affairs Office Fort Wainwright; Flickr CC BY 2.0
A variety of ceramic materials are finding their way into military vehicles and other technologies. Engine components, missile radomes, and personal/vehicular armor are just a few of the applications. For the last half century, ceramics have been used for personnel and light vehicle protection against small arms and machine gun threats. Whether it is protecting Americans at home or abroad, ceramics are a key enabler for this mission.
Ceramic armor protects soldiers
The distinct characteristics of advanced ceramics, including light weight, the ability to withstand extremely high temperatures, hardness, resistance to wear and corrosion, low friction, and special electrical properties, offer major advantages over conventional materials such as plastics and metals. Because of this, advanced ceramics are the foundation for the lightest, most durable body armor used for small to medium caliber protection available. Hot pressed boron carbide and silicon carbide ceramic is integrated with optimized composite structures to produce rugged multi-hit body armor plates.
Complete aircraft armor systems that include ceramic armor seats, components, and panel systems are found in the Apache, Gazelle, Super Puma, Super Cobra, Blackhawk, Chinook, and other military helicopters. Armor tiles are also specified in many fixed wing applications including the C-130 and C-17 aircraft. Single, double and triple curve plates and multi-hit armor systems featuring boron carbide and silicon carbide advanced ceramics are also used for special operations forces as body, side and shoulder armor. Advanced protection for other vulnerable body areas including hips, legs and arms is under development.
The U.S. Army is developing metal-ceramic and metal-ceramic-composite hybrids for improved performance. The first type is metal-encapsulated ceramic armor that allows delay of ceramic failure for improved ballistic performance due to better metal-ceramic bonding. The second type, found on the Stryker-Interim Armored Vehicle, uses a polymer matrix composite to catch any spall off the back of the metal. Future applications for ceramic-based armor include the US Marine Corps Expeditionary Fighting Vehicle (formerly known as the Advanced Amphibious Assault Vehicle, or AAUV) and the US Army’s Future Combat System.
Seeing better with transparent ceramics
Because many ceramic materials are transparent to certain types of energy, light or otherwise, they can be used for infrared domes, sensor protection, and multi-spectral windows. In addition to these optical properties, such ceramics have the desired abrasion resistance, strength, and thermal stability. A special type of glass-ceramic material shows promise for electromagnetic windows for use in artillery projectile because of its suitable electrical properties and high temperature capability.
Silicon nitride (a non-oxide ceramic) is used as radomes for missiles in the latest air defense systems. It was specifically selected for missile radomes because of its mechanical strength and dielectric properties. The material allows microwave or other energy to pass through to locate incoming targets. Its mechanical strength allows the missile system to withstand erosion and large temperature excursions while flying at hyper-velocity through the atmosphere. Also under development are transparent infrared windows using nanocrystalline yttria (a type of oxide ceramic) for missile applications.
Improved glasses and glass ceramics are also being considered for armor windows with the desired ballistic performance. Glasses can be produced in large sizes with curved geometries, and can be produced to provide incremental ballistic performance at incremental cost. A fused silica glass is one material under development.
Other transparent materials are being considered for windshields, blast shields, and sensor protection in aircraft. A ceramic material called spinel (magnesium aluminate) has superior optical properties within the infrared region, which makes it attractive in sensor applications where effective communication is impacted by the protective dome’s absorption characteristics.
Improving turbine engine efficiency
Future Army helicopters will be able to fly farther and carry more payload thanks to ceramics. Turbine engine operational efficiencies can be increased through the use of ceramic matrix composites and ceramic thermal barrier coatings due to their high temperature capability. Ceramics have the potential to operate at temperatures above 1100 C with minimal or no cooling. Composites are also 30 to 50% lighter than the metallic alloys currently in use. When composite combustor liner and turbine vane applications are coated with ceramics, operating temperatures increase to 1650C and the components are protected from the combustion environment. A multi-component ceramic coating based on hafnium oxide has survived a 300 hour test at 1650C.
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