Variation of the coefficient of thermal expansion with the volume ratio of TiB2-Sialon and its influence on the overall performance of PcBN

Abstract

In this study, the primary factors affecting the performance of PcBN (Polycrystalline cubic boron nitride) tool materials were investigated by high temperature/high pressure sintering through the variation of TiB2-Sialon volume ratio, the strength of TiB2-Sialon binder itself, as well as the matching of the average coefficient of thermal expansion (CTE) with cBN (Cubic boron nitride). The effects of TiB2-Sialon on the phase composition, microstructure, and mechanical properties of PcBN composites were studied by X-ray diffraction (XRD), universal testing machine, scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the properties of TiB2-Sialon binder are analogous to those of the corresponding composites. The phase composition of PcBN composite is not affected by the change of volume ratio. It was found that prepared composite, have TiB2 rod crystals growing along the (100) plane and Sialon rod crystals growing on the (001) plane. The influence of the volume ratio of TiB2-Sialon on the mechanical properties of the composites is principally concerned with the density, mechanical properties, and thermal expansion coefficient of the used binder. The extent to which the binder matches the coefficient of thermal expansion is favorable to the strength of the composite. When the volume ratio of TiB2 to Sialon was 1:3, the hardness (25.21 GPa, 37.44 GPa) and toughness (7.09 Pa m1/2 and 7.48 Pa m1/2) of TiB2-Sialon binder/TiB2-Sialon-cBN composites reached the maximum value, and the optimal impact resistance was also achieved. The density of the binder and the composite material was maximized when the volume ratio is 1:4. The average thermal expansion coefficient of the binder hoc tempore matches comparatively with cBN, and the interface bonding is better, displaying the best flexural strength (805.30 MPa and 1059.60 MPa) and wear ratio (2005). Therefore, adjusting the volume ratio of TiB2-Sialon within a certain range is beneficial to further enhance the binder's strength and mechanical properties.