Study On The Sintering Of CBN-AlN Composites At The HPHT

The developments and applications about synthetic cubic boron nitrogen (cBN) , Polycrystalline cubic boron nitrogen (PcBN) and the related materials were narrated in this paper. As new superhard materials continued with diamond, Cubic boron nitride has a high hardness and high thermal conductivity ranking next to diamond, and is superior to diamond in thermal stability. Because of those superior properties, cBN sintered compacts are widely used as cutting tools for cutting of hardened steel, cast iron, ferrous powder metal and heat resisting alloy.Conventional cBN sintered compacts are different with the solid sintering of cBN for themechanis of sintering, the performance of physics and chemistry. The binder materials, their content and distribution can directly affect the mechanical and thermal properties, thus have remarkable influence on cutting performance of the compact. Nowadays, the superior mechanical characters and high thermal conductivity of high content cBN composites with AiN-based binders have caused extensively attention.The effect of temperature on sintering of cBN-AIN composites at 5GPa and 1400℃～1700℃are studied in this work. The hardness, microstructure, and phase composition of the sintered cBN-A1N composites are found to be varied with the sintering temperature and the content of A1N. The recovered specimens are polished and investigated by hardness testing, scanning electron microscope (SEM), energy dispersive X-ray analysis (EDXA), X-ray diffraction(XRD), resistance of bend strength test and cutting test. It shown by the results of analyzed:The AIN aggregated in the sintering of cBN-AIN composites at the low temperature, the number and area of the aggregative AlN zone decrease gradually with increase of the sintering temperature. The pyknosis of cBN-AlN composites at 1700℃is better than other sintering temperature.The hardness of the sintered cBN-AlN composites increases with the sintering temperature, and reaches the maximum 3000kg/mm² at 1600℃in the sintering temperature range.The binding admixture of AlN took part in the chemical reaction at the HPHT sintering, and the new reaction phase is Al₂O₃, and the content increased with the higher sintering temperature.The resistance of bend strength test shown, the toughness of the sintered cBN-AIN composites related to the sintering temperature, and it increased at high temperature. There were intercrystalline fractures and transcrystallinefractures by the fracture analysis diagram. The intercrystalline fractures existed at low sintering temperature, and the transcrystalline fractures existed at the high sintering temperature.The cutting test shown that the cutting length of the composites of cBN-AIN for content of AlN was 15% and the sintering of 1600℃were propitious to other composites, and the cutting length up to 4000m, and the hardness isn't related to the life performance of cutting, the tools cut the chilled hardened steel if the hardness of tools come to certain quantity value;According the results of comprehensive analysis and test, the over-all properties of the composites of cBN-AlN for content of AlN was 15% and the sintering of 1600℃was best, and the cutting performance was propitious to other composites.