Effect of grain growth in bimodal microstructure on cutting performance of self-toughening Dy-α-SiAlON ceramic tool inserts

Although significant increase in mechanical properties has been achieved in ?-SiAlON ceramics by introducing self-toughening bimodal microstructure, the bimodal microstructure may not always result in better cutting performance of ?-SiAlON tool inserts. Herein Dy-?-SiAlON ceramics were prepared by hot-pressing at 1900?C under 30MPa. Diameter and aspect ratio of the large elongated ?-SiAlON grains pivotal to formation of bimodal microstructures were regulated by using 0-5wt.% Dy2O3 as a sintering additive. Mechanical properties and cutting performance of ?-SiAlON tool inserts were evaluated. The results showed good Vickers hardness (19.0-19.7GPa) and fracture toughness (3.61-4.18MPa?m1/2) increasing with crack propagation length. However, transverse section of the large elongated grains was revealed as critical crack to cause premature fracture of the ?-SiAlON ceramics. Fracture rather than attrition wear was recognized as dominant mechanism for tool failure, indicating that for better cutting performance of the ?-SiAlON tool inserts a selftoughening microstructure consisting of thinner grains with large aspect ratio is required.