Ceramic Materials: What is the Importance of Fracture Toughness?

Due to their unique thermodynamic characteristics, high strength ceramic materials are pervasively used in demanding industrial applications. Characteristically, advanced ceramics display tightly bonded, semi-crystalline structures with a tremendously dense microstructural arrangement throughout. This communicates changeable levels of material strength and resistance to chemical attack, all of which is dependent on the distinct chemical makeup of the ceramic.

Silicon (Si), aluminum (Al), oxygen (O), and nitrogen (N) are the four constituent elements that are bound together in one of three distinct crystalline phases, meaning sialons are unique ceramic materials. They are often seen combined with rare earth oxide sintering additives and exhibit a wide range of high-performance thermomechanical properties. They are a direct competitor of alternative technical ceramics such as alumina (Al2O3) and zirconium oxide (ZrO2).

Fracture Toughness: What is it?

Mechanical property of materials, fracture toughness describes how able material can resist fracture. In relation to engineering, the definition of a fracture is explained as a form of material failure in which it is put under stress caused by an impact force and fails catastrophically.

Usually, it is linked to the propagation of established flaws within the product such as cracks, defects, and voids. Following the densification of the green body or machining of the net shape, it is impossible to guarantee that ceramic materials will be completely flaw-free. As a result, determining the linear elastic fracture mechanics of a material is vital to be able to determine its ability to resist fracture.

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Image Credit: International Syalons

Ceramic materials are characterized with consideration of fracture toughness. This is done by calculating the energy required for a defect of known dimensions to propagate and develop into a crack. It is necessary to have an understanding of the material’s Young’s modulus and the length of the defect to measure what is referred to as the stress intensity factor.

After these parameters have been attained, there is a possibility to determine the fracture toughness of ceramic materials. This is expressed in terms of force per unit of surface area (MPa m½).

Fracture Toughness and its Importance

In almost any engineering application, fracture toughness is a vital material property to consider so that a system or component can be designed to withstand the the expected impacts during its lifetime in service.

Although technical ceramics do not typically display fracture toughnesses as high as most metals, nevertheless, some sialons and zirconia ceramics exhibit good fracture toughness properties to guarantee excellent resistance to the propagation of cracks and voids.

Ceramic Materials from International Syalons

Known as the strongest sialon ceramic available, Syalon 101 from International Syalons boasts a fracture toughness value of 7.7 MPa m½. This is outshined only by Zircalon zirconia products. These products display the following fracture toughness qualities:

  • Zircalon 5 - fracture toughness of 8.0 MPa m½
  • Zircalon 10 - fracture toughness of 10.0 MPa m½
  • Zircalon 30 - fracture toughness of 14-15 MPa m½

Based in Newcastle, UK, International Syalons is a ceramic materials specialist that was established in the 1970s. This was after leading pioneering research into the practical development of sialon ceramics as an alternative to established silicon nitride materials.

This information has been sourced, reviewed and adapted from materials provided by International Syalons.

For more information on this source, please visit International Syalons.

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