Study On Preparation And Properties Of Si₃N₄Matrix Ceramic Cutting Tool Materials

Si3N4matrix ceramics as the new cutting tool materials are suitable for cutting cast iron, superalloy and nickel-base alloy materials, especially for larger feed or interrupted cutting. Their main features are have higher bending strength and fracture toughness compared with Al2O3matrix ceramics. But the sintering of Si3N4matrix ceramics is difficult, and the hardness and wear resistance are lower compared with Al2O3ceramics. So the study on Si3N4matrix materials is backward compared with Al2O3matrix ceramics.Si3N4with particle diameters0.8m and0.35μm were used as initial powders,6wt%Y2O3and2wt%Al2O3were used as sintering aids. In order to improve the strength, toughness and service life of Si3N4matrix ceramic cutting tool materials, a small amount (1vol%～3vol%) of TiCo.7No.3were added as a hard second phase. The samples were hot-pressed at1650℃and30MPa in vacuum. The density, thrength, toughness and hardness were tested, scanning electron microscope (SEM) and x-ray diffraction (XRD) were used to analys the microstructure and the phases. The experimental results show that strength and tougheness are improved by addition of a small amount of TiC0.7N0.3. Because the growth of partial Si3N4grains were prevented, what makes β-Si3N4grains have different diameters and aspect ratios. The β-Si3N4grains staggered with each other. The bending strength and fracture toughness of the sample added1vol%TiC0.7N0.3are916MPa and9.47MPa-m1/2separately.The specimens of contains1vol%TiC0.7N0.3were hot-pressed at1650℃,1700℃and1750℃in vacuum separately. The results show that the microstructure are β-Si3N4grains with different diameters and aspect ratios staggered with each other. The average grain size of the specimens increased with increased hot-pressing temperature. The relative density, bending strength and fracture toughness increased with increased hot-pressing temperature and the value for the specimens of hot-pressed at1750℃are99.22%,993MPa and9.81MPa-m1/2separately. In order to improve the hardness and wear resistance of Si3N4matrix ceramic cutting tool materials, adding5wt%and10wt%CBN separately into the specimens of contains lvol%TiC0.7N0.3. The specimens were hot-pressed at1750℃and30MPa in vacuum. The results show that the CBN phase transformed from cubic to hexagonal BN during hot-pressing, and BN reacted with Y2O3to from YBO3what makes the content of liquid phases is too small. These two reasons lead to the properties of the specimen decreased with addtion of CBN.In this work, the Si3N4matrix ceramic cutting tool materials are strengthed and toughed by fine grain strengthening, particle toughening by the second Phase, crack bridging, crack deflection and pulling out of the β-Si3N4grains.