Effect of metal phases on microstructure and mechanical properties of Si3N4-based ceramic tool materials by microwave sintering

Abstract

Si3N4-based composite ceramic tool materials were fabricated by microwave sintering. The effects of Ni and Co on the mechanical properties, phase transformation and microstructure of the Si3N4-based composites were studied, and the toughening mechanism was analyzed. The optimum comprehensive mechanical properties with the relative density of 97.15 ± 0.2%, Vickers hardness of 17.28 ± 0.17 GPa and fracture toughness of 6.59 ± 0.12 MPa m1/2 were obtained at 1650 ℃ when the content of Ni was 2 wt%. Ni can promote the formation of grains with high aspect ratio more effectively than Co, but the hardening effect of Co was higher than Ni. Both of two metals would restrain the phase transformation of Si3N4 from α phase to β phase. The main toughening mechanism was the combined action of pulling-out of β-Si3N4 columnar crystals, crack bridging by columnar crystals and crack deflection.