Investigation On SiC/Si₃N₄ Bond Polycrystalline Diamond/cubic Boron Nitride Toughened With Y-ZrO₂

Y-ZrO2 toughened SiC bond polycrystalline diamond (PCD) and SisNt bond polycrystalline cubic boron nitride (PCBN) were prepared via high temperature and high pressure sintering. The effect of Y-ZrO2 powders preparation process, the compositions of the powders and the sintering process on the fracture toughness, the tension strength and the grinding-ratio was investigated by the use of mechanical tests. The microstructures of PCD and PCBN were analyzed by means of XRD, TEM and SEM. The toughening mechanism of them was discussed.The experimental results confirm the toughening effect of Y-ZrOi particles homogeneously distributed in the ceramic bond of PCD or PCBN. The toughening result depends on the stabilizing additive content in Y-ZrO2 powders, the powders preparation process as well as the sintering process of PCD and PCBN.Y-ZrO2 powders prepared through chemical co-precipitation (CP) are loosely floccule agglomerates with inhomogeneous sizes, while the powders prepared through boiling hydrolysis (BH) are composed of uniform particles (about O.lm in diameter). The density of BH zirconia compact sintered at 1350癈, 5GPa for 10~99s approaches its theoretic value. With prolonging sintering time, the volume fraction of tetragonal phase increases but Ct/a,-ratio decreases. It is thus evident that the stabilizing effect of Y2O3 on t-ZrO2 under the high pressure sintering is similar to that under the pressureless sintering.Y-ZrO2 toughened SiC bond PCD has been obtained via sintering at the temperature of 1350癈 and the pressure of 5GPa. The chemical reaction between ZrO2 and SiC doesn't take place. The particles of BH Y-ZrO2 disperse homogeneously in the bond of PCD. The volume fraction of tetragonal phase increases with the content of Y2O3 in ZrO2 powders and 100% tetragonal is reserved at room temperature as the powders is with above 2mol%Y2O3- The transformation of tetragonal to monoclinic phase is introduced by applied stress. The volume fraction of transformable tetragonal phase increases with the Y2Os content increasing and reaches the maximum at 2mol%Y2O3. The addition of Y-ZrO2 improves the fracture toughness of PCD and the grinding ratio also increases with the Y2O3 content increasing. The optimum comprehensive properties of PCD can be achieved as the Y-ZrO2 powders contain 2mol%Y2O3.Aluminum addition in Si3N4 or Si3N4 bond PCBN can prevent Y-ZrO2 powders from forming the nontransformable tetragonal phase. As a result the stress induced transformation toughening related to the addition of Y-ZrO2 is realized in nitrogen-containing ceramic matrix. In PCBN compact sintered at the temperature of 1400 and the pressure of SGPa using Si3N4 as bond and aluminum as sintering aids the optimum transformation volume fraction from tetragonal to monoclinic phase has been obtained at 2.0mol% Y2O3 in Y-ZrO2 powders that also corresponds to the optimum comprehensive properties including high level of fracture toughness, tensile strength and wear resistance.The toughening mechanism of Y2O3 stabilized ZrO2 in SiC bond PCD and SiaN4 bond PCBN includes the stress induced transformation toughening and the microcrack toughening.