Silicon Nitride – Engineering Ceramic Solutions
Silicon nitride (Si3N4) is a high performance advanced ceramic. Developed for extreme applications, it combines excellent strength, fracture toughness and thermal shock resistance. As such, it is often used to replace metal components, especially where high hot strength, creep resistance and oxidation resistance are required. It is also suited to performing in extreme operating conditions that can often lead to the rapid demise of even the most refractory alloys.
In applications where it has replaced metals and alloys, silicon nitride can often result in:
- Potentially higher levels of efficiency – Si3N4 can enable you to operate at faster speeds due to its high temperature stability
- Longer component lifespan
- Less downtime and maintenance
- More precise operation – due to higher wear resistance
Origins of Silicon Nitride
Silicon nitride was originally developed in the 1960’s and 1970’s in the search for fully dense advanced ceramics with high strength and toughness that could potentially replace metals in advanced turbine and reciprocating engines.
Types of Silicon Nitride
There are 3 main types of silicon nitride. They are:
- Reaction bonded Si3N4 (RBSN)
- Hot pressed Si3N4 (HPSN)
- Sintered silicon Si3N4 (SSN)
RBSN is produced by firing a silicon powder compact in a nitriding atmosphere. The need for nitrogen ingress to complete the conversion to silicon nitride means that full density is hard to achieve.
Hot pressing and sintering with carefully selected sintering aids are processes better suited to producing fully dense silicon nitride components. Fully dense components result in superior physical properties that are capable of higher levels of performance, especially in more demanding environments.
Due to the vastly different ways in which they are produced, the properties of each type differ.
Typical Properties if Silicon Nitride Advanced Ceramics
Silicon nitride is characterised by:
- Low density
- High strength over a wide temperature range
- Low co-efficient of thermal expansion
- Superior thermal shock resistance
- Excellent wear resistance (both impingement and tangential)
- Excellent fracture toughness – making it highly resistant to impacts and mechanical shocks
- Excellent mechanical fatigue and creep resistance
- Good oxidation resistance
- Good chemical resistance
- Normally grey to black in colour
Si3N4 ceramics can be polished to a high surface finish resulting in low friction surfaces for wear faces.
Silicon nitride was originally developed for automotive components subjected to the most severe operating conditions such as turbocharger rotors. Its increasing acceptance as a suitable alternative to metals and alloys have seen it used in far less exotic applications such as bearings in fidget spinners.
Other applications where Si3N4 has been used include:
- Metal cutting and shaping tools
- Hot metal handling e.g. spouts and nozzles
- Glow plugs in diesel engines
- Wear components e.g. high precision shafts and axles
- Turbine blades