This transformation is accompanied by a growth of elongated β phase at the expense of equiaxed α-phase, as shown in Fig. 1 below.
Sialon ceramics or Silicon Nitride and SiAlONs are the materials possessing unique combination of fracture toughness, hardness and strength and have potentials to be used in many industries.
A strive to further increase the reliability of these Sialon ceramics led to the use of many sintering aids and densification methods involving pressure and elongated pressureless sintering.
The problem associated with the fabrication of these ceramics has been how to impart high fracture toughness and, at the same time, retain high hardness and strength.
The key micro structural feature which controls the strength and toughness of Sialon ceramics is the α→β phase transformation which takes place during densification at high temperature.
This type of microstructure provides combination of high fracture toughness and hardness (Table I) not found in commercially available materials.
High fracture toughness and high hardness make this class of ceramics suitable for applications where only metals and composite are used, including cutting tools for machining steel and nonferrous alloys, engine components and parts in metals smelting industrie.
Tests have shown this ceramic to exhibit excellent performance in cutting operation against cast iron and steel and serves as a substitute for alumina-whiskers cutting toll with added advantage of having increased inertness in contact with iron during high speed cutting.
In addition to inadequate fracture toughness and hardness of classical silicon nitride ceramics, high reactivity with work-piece has been the main problem facing the existing silicon nitride-based ceramics in cutting operations.
Reaction-assisted wear of the tool during machining of steel was the largest impediment for the wider use of silicon nitride as tool material in machining steel and nonferrous alloys.
The new generation of SiAlON ceramics developed by www.sialon.com and partners has been shown to significantly improve the shock resistance and decrease wetting by molten aluminum, making it highly attractive for the fabrication of crucibles, tubes and fixtures used in metal smelting operations.