作者: Zhi Hong Li, Y.M. Zhu, Xia Wan Wu, Q.M. Yuan, Zheng Fang Yang
33
作者: Mikinori Hotta, Takashi Goto
摘要: SiAlON-cubic boron nitride (cBN) composite was prepared by spark plasma sintering (SPS) using -SiAlON and cBN powders as starting materials, and the effect of holding time on densification, phase transformation and hardness of the composite was investigated. The SiAlON-cBN composite containing 20 vol% cBN sintered at 1650oC for 60s was densified to >97% of theoretical density. cBN phase transformed to hexagonal boron nitride (hBN) in the SiAlON-cBN composite with increasing holding time at 1650oC. Vickers hardness of the SiAlON-20vol%cBN composite sintered at 1650oC for 60-300s was 17.7GPa, and the hardness decreased with increasing holding time.
241
作者: B. Zhang, Wen Feng Ding, Jiu Hua Xu, Q. Pan, Y.J. Shi
摘要: Abrasive composite bulks consisting of polycrystalline cubic boron nitride (PCBN) grains, Cu-Sn-Ti alloy and graphite particles were sintered at the heating temperature of 920 °C for the dwell time of 30 min. The bending strength of abrasive composite bulks was measured. The interfacial microstructure and the phases were characterized. In addition, the dressing experiment was carried out to detect the self-sharpening behavior of the composite bulks. Results obtained show that the abrasive composite bulks in this investigation give higher bending strength than that of the vitrified abrasive wheels. The compounds of TiN, TiB2 were formed and the PCBN grains were embedded firmly. Strong fixing of the bulks to the PCBN grains led to the breakage of the PCBN grains when the abrasive composite bulks fractured. The intergranular fracture mode of the PCBN grains ensured the self-sharpening effect of the grains.
220
作者: Wen Feng Ding, Jiu Hua Xu, J.L. Huang, Z.Z. Chen, H.H. Su, Y.C. Fu
摘要: Self-lubrication CBN abrasive composite blocks and corresponding grinding wheels were made through the sintering process of CBN grains, graphite particles and Cu-Sn-Ti alloy at 920° for 30 min. The mechanical strength of the composite blocks was measured by means of the three-point bending experiments. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) were employed to characterize the fracture morphology and the interfacial microstructure of the composite blocks. Dressing experiments were carried out and the graphite film on the CBN grain surface was observed. The results obtained show that the bending strength of the composite blocks with 5 wt.% graphite particles reached 116 MPa, which met the mechanical requirements of the working layer of the grinding wheels. Chemical joining has taken place at the interface of CBN/Cu-Sn-Ti and graphite/Cu-Sn-Ti during the sintering process. Graphite film has been formed and spread to the grain surface after dressing.
85
作者: Ana Lúcia Diegues Skury, Shirlene Chagas, Guerold Sergueevitch Bobrovinitchii, Sérgio Neves Monteiro
摘要: Compositions of cutting tools based on cubic boron nitride phase added with different ceramics as binders have been the subject of several works. A major problem of these tools during machining of steel is the loss of cutting efficiency due the "chemical weathering" generated by the reaction between iron and cBN at the high temperatures reached by the machining operations. Aiming to eliminate these problems, this paper presents results on the development of composites obtained by sintering process at high pressures and high temperatures in association with a cyclic operation. Si3N4 was used as the binder agent. The compacts were analysed by x-ray diffraction as well as optical and scanning electron microscopy. The mechanical properties were evaluated by means of microhardness and fracture toughness tests. The degree of phase transformation of the Si3N4, the chemical reaction during the cyclic sintering process, and the sintering mechanism of the additive were discussed.
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