Silicon nitrides (Si3N4) have an excellent combination of material properties. They are almost as light as silicon carbide (SiC), but due to their microstructure they have very good thermal shock resistance and are insensitive to knocks and impacts, which they owe to their very high fracture toughness.
Very low density (3.21 g / cm3) Very high fracture toughness (7 MPam1 / 2) Good flexural strength (850 MPa) Very good thermal shock resistance: high thermal stress parameter (569 K) Maximum operating temperature in an oxidizing atmosphere 1300 ° C Maximum operating temperature in a neutral atmosphere 1600 ° C
The structure consists of stem-shaped crystals that interlock as micro rods.
One application in which this combination of properties has proven particularly successful is the machining of gray cast iron or cast iron with ceramic indexable inserts.
In contrast to hard metals or other cutting materials, when using ceramic indexable inserts, the processes can be carried out at the highest speed and free of coolant.
The combination of good tribological properties and very good fracture toughness also makes silicon nitride ceramics ideal for use as balls and rolling elements for lightweight and extremely precise bearings. Highly stressed tools for metal forming and robust and resistant components in automobile construction are further areas of application for Si3N4 ceramics.
The good thermal shock resistance and high temperature resistance is used in welding processes.