There are basically two types of ceramics. The traditional ceramics, also known as old ceramics, such as glass, pottery and chinaware, and new ceramics, also know as fine ceramics, that posses high heat and corrosion resistance properties. As a cutting tool material, new ceramics such as alumina (Al2O3, silicon nitride (Si3N4), sialon (SiAlON) and silicon carbide (SiC) are the most commonly used.
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Use of ceramics
Unlike cemented carbides and cermets, ceramics do not contain a binder metal. Therefore ceramics are extremely hard and posses high thermal stability. This allows ceramic tool grades to be used for high-speed machining applications. However there is one disadvantage with ceramics, and that is they do lack toughness and are prone to fracture. As a result, manufacturers have strived to develop ceramic grades with higher toughness.
Typical ceramics used for cutting tools are alumina based and silicon nitride based ceramics. Alumina based ceramics includes white, pure alumina ceramics (Al2O3 base, generally termed White ceramics), and black, Al2O3 TiC ceramics (generally termed Black ceramics) this type has carbide added to alumina to enhance the toughness properties.
Silicon nitride ceramics (Si3N4 base) posses both higher toughness and transverse rupture strength properties. However the silicon nitride ceramics do not posses the same hardness properties as the alumina ceramics. Therefore, to increase the wear resistance properties it is common practice to apply a coating to the silicon nitride ceramic grades.
Microstructure of ceramics