Fabrication Of Al₂o₃/ti(c, N) And Si₃n₄ Cutting Tool Materials

The advanced ceramic cutting tools have excellent characteristics such as high hardness,high melting point,good chemical stability and mechanical stability at high temperatures,and good machinability. They have excellent protential to be used widely in the field of machining.However, the brittle nature of ceramic materials restricts their applications.Recently, extensive work has been done on the strenthening and toughening of ceramic cutting tool materials.This work,aiming at improving the fracture toughness and bending strength,investigates the fabrication and properties of high performance Al2O3/Ti(C,N) and Si3N4 ceramic cutting materials.Al2O3/Ti(C,N)-TiNi composites were synthesized using hot-pressing method by adding TiNi in order to improve the toughness of the materials.The effect of content of TiNi on properties of the composites and the toughening mechanism were analyzed.The results show that the fracture toughness of Al2O3/Ti(C,N)-TiNi composites increases with increasing content of TiNi.The main toughening mechanism is particle dispersion strengthening and crack bridging. The optimum mechanical properties were achieved for the composite with 5wt% TiNi hot-pressed at 1550℃for 15 minutes under 30MPa pressure with Ar protection.The bending strength,hardness and fracture toughness of the composite are 523 MPa,18.23 GPa and 7.9 MPa·m1/2,respectively, higher than those for the pure Al2O3/Ti(C,N) ceramic composites.In order to investigate the effect of size of the initial powder on the microstructure and mechanical properties,Si3N4 ceramic materials were made by hot pressing at 1750℃for 60 min using Si3N4 powders with particle diameters of 0.5μm and 1μm,and powder mixtures of (95wt%0.5μm+5wt%1μm), respectively.3wt% Al2O3 and 7wt% Y2O3 were used as sintering aids.The results show that the hot-pressed Si3N4 specimens were composed of overlapping of rod-likeβ-Si3N4 grains with various aspect ratios. the fracture surface was rough and grain pull-out was clearly visible. The specimen made by 95wt% 0.5μm+5wt%1μm Si3N4 initial powder have the highest fracture toughness(14.2 MPa·m1/2).The most frequently observed toughening mechanisms in the specimens are crack bridging and crack deflection.