Gradient structures in SiAlON's for improved cutting performance

For a good cutting performance, hardness and fracture toughness are very important, particularly at heavy mechanical and thermal load. At the present time beta-Si3N4 or beta'-SiAlON ceramics are used in machining of cast iron and other difficult - to - cut materials. The presentation/paper deals with the possibility to combine the advantages of both SiAlON - phases by the controlled change of the outer region of a beta'-SiAlON insert to alpha' SiAlON in such a manner that a functionally graded structure is achieved. Microhardness measurements and different characterisations of the microstructure show this effect and the potential for practical use is outlined.