One of the earliest successful applications of sialon and silicon nitride advanced ceramics was as a cutting tool or throw-away insert for cutting or machining nickel based alloys. For these metal forming applications, the cutting tips must have a unique combination of wear, corrosion and thermal properties, which the silicon nitride and sialon ceramics offered by International Syalons exhibit.
Metal removal generates tremendous heat and even when a coolant is used, temperatures of 1000°C at the cutting edge are commonplace. If a cutting tip has poor thermal conductivity, then the heat generated cannot be easily dissipated. The thermal damage is exacerbated by high thermal expansion coefficient and crater wear develops leading to the rapid destruction of the cutting edge. This thermally induced wear is an important and neglected feature of metal removal.
Most turning operations involve ‘interrupted’ cutting, whether by design or accident. For example, in the turning of a roll of chill-cast iron the existence of pin holes and local asperities makes the cutting action intermittent. Many metal removal operations are by necessity discontinuous and as well as having suitable thermal properties, cutting tools must be tough.
In addition, work pieces are often hard and can be abrasive so the cutting tip should have a high hardness value. Finally, the metallurgical properties of the work piece may be such that at the high temperatures generated a chemical reaction takes place between the cutting tool and the work piece. So chemical stability is also important.
This demanding set of requirements is met by Syalon 050, a super hard advanced silicon nitride based sialon ceramic. It is thermally stable up to 1400 °C, thermal shock resistant, hard, tough and strong and chemically resistant to corrosion. In use, Syalon 050 cutting tools reduced by 75% the machining time for turbine discs for a Rolls Royce engine.