Graphite as reinforcement phase in metal matrix composite ( MMC)

Graphite as
reinforcement phase in MMC


  • Graphite is an allotrope of
    carbon which is a most stable form of carbon under standard
    condition. 
  • Graphite can be found in a
    flake form of graphite which has crystalline structure and has honeycomb
    hexagonal structure when edges are unbroken. Sometimes very fine flake of
    graphite is called amorphous. 
  • Generally, the thermal
    properties of graphite are anisotropy in nature. 
  • Graphite has several layers and
    the individual layer of graphite is called graphene sheet and each
    graphene sheets are joined together by weak van der Waals by virtue of
    which low friction is created between adjacent graphene sheets this
    determine self- lubricating properties of graphite. 
  •  Each layer of graphene is
    arranged in a honeycomb lattice structure with a bond length of 0.142 nm
    and the angle between each bond is 1200. 
  • Graphite is rarely found in the
    form of mono-crystals, and mostly found in the form of flakes or lumps.
    Graphite is formed by hexagonally arranged layers of carbon atoms in a
    condensed planer ring system.

Graphite is commonly used as a reinforcement phase in Metal Matrix Composites (MMCs). MMCs are materials composed of a metal matrix that is reinforced with a secondary phase, which can be a ceramic, polymer, or carbon-based material like graphite.

The addition of graphite as a reinforcement in MMCs offers several advantages. Some of these advantages include:

Lightweight:

Graphite has a low density, which contributes to the overall lightweight nature of MMCs. This property is particularly beneficial in applications where weight reduction is essential, such as aerospace and automotive industries.

High strength-to-weight ratio:

Graphite has high tensile strength and stiffness, allowing it to enhance the mechanical properties of the MMC. The combination of the metal matrix and graphite reinforcement results in improved strength and stiffness while maintaining a relatively low weight.

Thermal stability:

Graphite exhibits excellent thermal stability, enabling MMCs to withstand high-temperature environments without significant degradation. This property is advantageous in applications where the material is exposed to elevated temperatures, such as in engine components or aerospace applications.

Lubricity:

Graphite has self-lubricating properties, which can be advantageous in applications where friction and wear need to be minimized. The presence of graphite in MMCs can reduce the coefficient of friction and improve the tribological performance of the material.

Thermal conductivity:

Graphite has a high thermal conductivity, making it an excellent choice for enhancing the thermal management properties of MMCs. The addition of graphite can enhance the heat dissipation capabilities of the material, making it suitable for applications that require efficient thermal conductivity.

Electrical conductivity:

Graphite is an excellent electrical conductor. When incorporated into a metal matrix, it can enhance the electrical conductivity of the composite material. This property is advantageous in applications that require efficient electrical conductivity, such as electronic components and power transmission systems.

Damping capacity:

Graphite has inherent damping properties, meaning it can absorb and dissipate mechanical vibrations and energy. Incorporating graphite into an MMC can improve its damping capacity, making it suitable for applications where vibration damping is essential, such as in structural components for aerospace or automotive industries.

Machinability:

Graphite is relatively easy to machine compared to many other reinforcement materials. It has low wear on cutting tools and can be machined with high precision. This makes it easier to manufacture complex shapes and components from MMCs containing graphite reinforcement.

Tailorable properties:

The properties of graphite-based MMCs can be modified by controlling factors such as the volume fraction and orientation of the graphite reinforcement. By adjusting these parameters, it is possible to tailor the mechanical, thermal, and electrical properties of the composite to meet specific application requirements.

Cost-effectiveness:

Graphite is generally less expensive compared to other reinforcement materials, such as ceramic fibers or carbon fibers. This cost advantage makes graphite-based MMCs an attractive option in applications where performance requirements can be met without incurring the higher costs associated with other reinforcements.

Compatibility with different metal matrices:

Graphite can be used with a variety of metal matrices, including aluminum, magnesium, titanium, and their alloys. This versatility allows for the customization of MMCs based on the desired combination of properties and the specific requirements of the application.

Improved wear resistance:

The incorporation of graphite as a reinforcement phase can enhance the wear resistance of the MMC. Graphite’s lubricating properties reduce friction and wear between the matrix and other surfaces, making the material more resistant to wear and extending its service life.


Corrosion resistance:

Graphite has inherent corrosion resistance, particularly in non-oxidizing environments. When used as a reinforcement in MMCs, it can help improve the overall corrosion resistance of the material. This is beneficial in applications where the composite is exposed to corrosive substances or environments.

Thermal expansion matching:

Graphite’s coefficient of thermal expansion is relatively low, which can help improve the compatibility between the reinforcement and the metal matrix in terms of thermal expansion. By matching the thermal expansion coefficients, the risk of delamination and cracking within the composite can be reduced.

Enhanced damping at high temperatures:

Graphite-based MMCs can maintain their damping properties even at elevated temperatures. This is particularly useful in applications that experience high-frequency vibrations or mechanical shocks at elevated operating temperatures, such as aerospace or high-performance racing industries.

Fabrication flexibility:

Graphite reinforcement can be introduced into the metal matrix using various fabrication techniques. It can be added as particles, fibers, or whiskers, or in the form of preforms or coatings. This flexibility in fabrication methods allows for the production of MMCs with tailored microstructures and properties.

Impact resistance:

The incorporation of graphite reinforcement can improve the impact resistance of the MMC. Graphite’s ability to absorb and distribute impact energy helps prevent crack propagation and enhances the material’s resistance to impact loading.

Environmental friendliness:

Graphite is a naturally occurring material and is considered environmentally friendly. It is non-toxic and can be easily recycled, making it a sustainable choice for reinforcement in MMCs.
Non-magnetic properties: Graphite is non-magnetic, which can be advantageous in applications where magnetic interference needs to be minimized, such as in electronic devices or sensitive measurement instruments.

Surface finish and aesthetics:


Graphite-based MMCs can exhibit desirable surface finishes and aesthetics due to the presence of graphite particles. This can be beneficial in applications where appearance plays a role, such as decorative or consumer products.


It’s important to note that the specific performance benefits and limitations of graphite as a reinforcement phase may vary depending on the manufacturing process, composite architecture, and the specific application conditions. Therefore, comprehensive testing and characterization are necessary to ensure the suitability of graphite-based MMCs for a particular application.

However, it’s worth noting that graphite also has some limitations as a reinforcement phase. It is prone to oxidation at high temperatures and may experience degradation in the presence of moisture or corrosive environments. Additionally, the anisotropic nature of graphite can affect the overall mechanical properties of the MMC, as its properties may vary based on the direction of load application.

Overall, graphite as a reinforcement phase in MMCs offers a unique combination of properties that can be beneficial in various applications, especially where lightweight, high strength, thermal stability, and lubricity are required.



Graphite as reinforcement phase in metal matrix composite ( MMC)

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