Mechanical properties and microstructure of Al2O3-SiCw ceramic tool material toughened by Si3N4 particles

Abstract

Al2O3-SiCw toughened ceramic tools play vital role in high-speed machining of nickel-based superalloys due to their superior mechanical properties. Herein, owing to synergistic toughening mechanism, α-Si3N4 particles are employed as reinforcement phase into Al2O3-SiCw ceramic composite to optimize mechanical properties of Al2O3-SiCw ceramic tools. Moreover, the influence of Si3N4 content and sintering parameters on microstructure and mechanical properties of Al2O3-20 vol%SiCw ceramic tool material is systematically investigated. Results reveal that appropriate amount of Si3N4 particles is required to effectively increase the density of Al2O3-SiCw ceramic composites. The presence of Si3N4 particles leads to formation of novel β-sialon phase during hot-press sintering, which effectively enhances fracture toughness and flexural strength of Al2O3-SiCw ceramic composites. It is observed that grain size of newly formed β-sialon phase is extremely sensitive to hot-pressing sintering conditions. The degree of chemical transformation of α-Si3N4 into Si6-zAlzOzN8-z (β-sialon) and z-value of Si6-zAlzOzN8-z are significantly influenced by sintering temperature. Overall, Al2O3-20 vol%SiCw-15 vol%Si3N4 ceramic tool material, with 1.5 vol%Y2O3-0.5 vol%La2O3-0.5 vol%CeO2 (YLC) sintering additive, rendered optimal mechanical properties after sintering at 1600 °C under 32 MPa for 30 min. Improved mechanical performance can be ascribed to synergistic toughening and strengthening influence of whiskers and particles.