Silicon Carbide Ceramic Matrix Composite (CMC) is an advanced material used for high temperature applications like gas turbine engine hot sections. While traditional ceramics oxidize at higher temperatures, non-oxide CMC materials like Carbon/Silicon Carbide (C/SiC) provide good corrosion resistance and mechanical properties.
Long ceramic fiber reinforcements in these materials provide a regulated bridging effect that stops crack propagation when stress levels exceed their proportional limits, giving these materials high fracture toughness and preventing abrupt brittle failure that is often seen with monolithic ceramics.
Corrosion Resistance
CMC corrosion resistance largely depends on its interphase material and reinforcing materials, with CMCs boasting exceptional thermal, mechanical, dimensional stability as well as being capable of withstanding high temperatures – qualities which make them suitable for many aerospace industry applications.
CMCs are durable materials that can withstand both high temperatures and extreme pressures, making them suitable for aerospace applications such as turbines. Being lighter than their traditional aircraft components makes CMCs even more fuel-efficient for commercial jets.
CMCs consist of a ceramic matrix composed of silicon carbide (SiC), zirconium oxides, titanium nitride, aluminum nitride or other ceramic materials such as silicon carbide. To reinforce it, reinforcing fibers are attached either continuously or discontinuously and woven together into fabric to reinforce it further. Impregnating them with resin impregnation processes that either completely cure or partially cure prior to lay up makes up their first stage (prepreg fabrication process), before multiple layers stacked upon one another determine the final characteristics of CMC.
Interphase material acts to bond matrix and fibers together, increasing adhesion while efficiently transmitting stress. Furthermore, it limits crack formation and propagation while improving fracture toughness; CMCs with long fiber reinforcement typically incorporate either boron nitride or alumina material as the interphase material.
High Strength
Silicon carbide ceramic matrix composites (CMCs) offer significant advantages over metal alloys for gas turbine applications. Their ability to withstand dynamic loads and be made extremely thick without losing strength allows them to provide necessary stiffness and strength in hot sections of jet and other gas turbines, as well as being much lighter than their nickel superalloy counterparts, helping reduce weight and fuel consumption of such equipment.
CMCs possess a brittle behavior, yet are less prone to crack propagation within the material and critical failure. This is thanks to an interphase between fibres and matrix which acts as an effective mechanical fuse – deflecting matrix microcracks away from fibres thus avoiding fracture [102].
Interphase material typically comprises boron nitride; however, other materials suitable for its environment have also been utilized, including hafnium, zirconia and alumina – providing additional creep resistance properties to the product.
Liquid Polymer Infiltration (LPI), the main route of fabrication for these advanced ceramics, requires a unique type of furnace capable of providing excellent thermal uniformity across the melt pool as well as precise temperature control. L&L Special Furnace Co is one of the premier suppliers of such furnaces that are used to manufacture SiC CMCs for various applications.
High Modulus
Silicon carbide has many applications due to its exceptional mechanical properties at elevated temperatures. It is highly durable, has a low coefficient of thermal expansion and resistance against corrosion and oxidation.
Ceramic matrix composites can withstand the demanding environmental conditions associated with high-temperature applications, such as aerospace engines and reentry spacecraft. Ceramics matrix composites have proven themselves capable of withstanding thermal shocks and mechanical loads in oxidizing environments for extended periods, unlike metallic superalloys or monolithic ceramics which may degrade over time.
CMCs can achieve bend strengths exceeding 700 MPa and fracture toughness values exceeding 17 MN m-3/2 at room temperature and 1000 degC, respectively. Furthermore, their strength can remain unaffected even under high stresses for extended periods. This performance can be attributed to partial sintering or blunting of sharp defects where stress could concentrate and maintaining its strength and stiffness in this way.
Silicon carbide fibers and whiskers can enhance the mechanical properties of CMCs significantly, reinforcing them to stop cracks from propagating further and increase fracture resistance substantially.
Dispersed reinforcements such as platelets, particles, hafnia or zirconia may also improve the mechanical properties of CMCs; however they require additional processing steps for integration and cannot provide as high performance levels as continuous fibers.
High Durability
Silicon carbide ceramic matrix composite is an emerging technology with widespread application in high performance applications like aircraft engines and brakes. Due to its outstanding heat tolerance properties, silicon carbide ceramic matrix composite has become the material of choice for hot section components, safety-critical components and brake components in aerospace, energy and transportation sectors – although its brittleness and anisotropy present challenges when machined.
In order to address this challenge, various machining strategies have been created specifically for CMC manufacturing. Of these strategies, reactive melt infiltration (RMI) remains the most popular. RMI relies on capillary forces moving molten metal through porous preforms in reinforcing materials without applying pressure.
Infiltration creates a nearly-net shape for the ceramic, giving it superior failure strain capabilities when used as part of a ceramic matrix composite material.
Due to this being comprised of preceramic polymers that have been decomposed in an atmosphere containing nitrogen or ammonia (N2/NH3) at 800-1300 degrees Celsius pyrolytically decomposition produces a matrix made up of silicon nitride matrixes with ceramic particles as part of its final product.
Reinforcing monolithic silicon carbide with long fiber reinforcements can reduce its brittleness, increasing fracture toughness and making the material suitable for high mechanical stresses, making it suitable for applications such as aerospace engine hot area elements and nuclear reactor components.