Aerospace and Defense

Alumina (Al₂O₃), zirconia (ZrO₂), silicon carbide (SiC), and silicon nitride (Si₃N₄) play an indispensable role in the aerospace and defense industry. They are key materials for achieving high performance, high reliability, and breakthrough technological advantages.

In the aerospace and defense sector, material selection is extremely demanding, often centered around the three core requirements of "weight reduction and range extension," "extreme environment resistance," and "ultra-high performance."

1. Alumina (Al₂O₃): "The economical and reliable guardian." It provides excellent electrical insulation, wear resistance, and corrosion resistance at a relatively low cost, and is used in a variety of basic but critical components.

2. Zirconia (ZrO₂): "The tough master of disguise." Known for its extremely high toughness, it is also an excellent thermal barrier coating material with unique applications in the defense and engine fields.

3. Silicon Carbide (SiC): "The king of high-temperature and radar applications." Its exceptional high-temperature strength, thermal conductivity, and ablation resistance make it a core material for next-generation engines and radar systems. Its lightweight and high-stiffness also make it an ideal optical structural material.

4. Silicon Nitride (Si₃N₄): The "pride of high-performance bearings." It boasts the best overall mechanical properties (strength, toughness, and low density), making it particularly suitable for high-speed, high-load, and corrosion-resistant bearings and engine components.

1. Alumina (Al₂O₃)
Advantages: High hardness, excellent electrical insulation, good chemical stability, corrosion resistance, and relatively low cost.

Specific Applications:

• Radar Windows and RF Radomes: Radomes for airborne and missile-borne radars must allow microwave penetration while protecting the delicate antennas within. Alumina has moderate dielectric properties and is used in radomes for certain frequency bands.
• Electronic Packaging and Insulators: Used in circuit boards, insulators, and vacuum feedthroughs in avionics equipment to ensure circuit reliability in high-vibration and wide-temperature environments.
• Wear-Resistant Components: Used in wear-resistant bushings and sealing rings in helicopter rotor systems and servo actuation systems.
• Protective Armor: As part of composite armor (typically combining alumina ceramic plates with a composite backing), it is used in attack helicopter seats, personnel body armor, and light armored vehicles, where its high hardness can fragment warheads.

2. Zirconia (ZrO₂)
Advantages: Highest fracture toughness among ceramics (excellent impact resistance), low thermal conductivity (excellent thermal insulation), and high coefficient of friction.

Specific Applications:

• Thermal Barrier Coatings (TBCs): This is its most important application. Yttria-stabilized zirconia (YSZ) is applied to the metal surfaces of aircraft engine turbine blades and combustion chamber inner walls through methods such as plasma spraying. It provides excellent thermal insulation, allowing the engine to operate at higher gas temperatures, significantly improving efficiency and thrust.
• Wear-Resistant and Friction Components: Utilizing its high toughness, it is used in certain wear-resistant gaskets, seals, and other components requiring high friction in aircraft engines.

3. Silicon Carbide (SiC)
Advantages: Extreme high-temperature strength (virtually no loss of strength above 1600°C), extremely high thermal conductivity (excellent heat dissipation), low thermal expansion coefficient (excellent dimensional stability), excellent ablation and creep resistance, high hardness, and suitability as a wide-bandgap semiconductor.

Specific Applications:

• Next-generation aircraft engine hot section components: Used in the manufacture of non-rotating parts such as combustion chamber liners, turbine outer rings, and guide vanes. SiC ceramic matrix composites (CMC-SiC) are lighter and more heat-resistant than nickel-based superalloys, making them a core material for reducing weight and improving efficiency in next-generation engines.
• Hypersonic aircraft: Used in the most demanding areas such as nose cones, leading edges, and wing leading edges. SiC and its composites can withstand aerodynamic heating exceeding 1600°C and the harsh ablation environment, ensuring the aircraft's external integrity and the safety of its internal equipment.
• Optical and Structural Parts: Due to its high stiffness, low density, and excellent thermal stability, it is used in the manufacture of large space telescope mirror blanks, satellite reflectors, laser mirrors, and other applications, ensuring imaging accuracy in space environments.
• Military Radar and Electronic Warfare: SiC, as a wide-bandgap semiconductor, is used in the manufacture of high-power, high-frequency microwave radio frequency devices and power modules. It enables longer-range and higher-efficiency radar detection, higher-power electronic warfare equipment, and greater resistance to high temperatures and radiation.
• Armor Protection: Used in high-end armored vehicles and pilot protection, its hardness and multiple-strike resistance surpass those of aluminum oxide.

4. Silicon Nitride (Si₃N₄)
Advantages: Excellent thermal shock resistance (resistance to rapid cooling and heating), high fracture toughness and flexural strength, low density (second only to carbon materials), self-lubricating, and corrosion-resistant.

Specific Applications:

• High-Performance Aviation Bearings: This is its classic application. Used in turbine engine main shaft bearings. Compared to traditional steel bearings, Si₃N₄ bearing balls have a 60% lower density, significantly reducing centrifugal forces, allowing for higher engine speeds (improving efficiency). They also offer high-temperature resistance, a longer lifespan, and the ability to temporarily operate even in the event of lubrication failure (fail-safe).
• Engine Components: Used in the manufacture of turbine rotor blades, fuel nozzles, and other components. Their high-temperature resistance and low density contribute to improved thrust-to-weight ratios.
• Missile and Spacecraft Components: Used in precision bearings for gyroscopes in missile guidance systems, ensuring high accuracy. They are also used in high-temperature structural components on spacecraft.