Papers by Keyword: Cubic Boron Nitride (CBN)

Abstract: Nanocomposite WC-10Co powder produced by spray pyrolysis-continuous reduction & carbonization technology and cubic boron nitride (CBN) plated with titanium by vacuum vapor deposit were used, and this paper adopted spark plasma sintering (SPS) process to prepare CBN enhanced ultrafine WC-10Co cemented carbide cermets composite material. The microstructure and mechanical properties of CBN-WC-10Co composites were investigated. The results show that CBN-WC-10Co composites consolidated by spark plasma sintering can reach 95.0 % relative density, and transverse rupture strength (TRS) is 1050 MPa, the average grain size of cermets matrix is less than 420 nm, and CBN-WC-10Co composites with excellent properties are achieved. The CBN still remains very good crystal shape after 1240°C spark plasma sintering, and there is not obvious clearance between CBN plated with titanium and the cermets matrix, the coated titanium layer can not only improve the thermal stability of CBN, but also increase the properties of CBN-WC-10Co composites.

Abstract: In this paper, the performances of CBN abrasives with and without Ti coatings and their changes during heat treatment were investigated under the same conditions. The results showed that the single particle compressive strength and the impact toughness for CBN abrasives with Ti coatings were lower than these of CBN abrasives without Ti coating. Ti coating on the surface of CBN abrasive particles oxidized and formed TiO2 with discontinuous structure at above 650°C during the firing process. The poor oxidation resistance of Ti coating and the discontinuous structure of its oxidation product could not protect CBN abrasives from heat damage, therefore could not improve properties of CBN abrasives.

Abstract: Cubic boron nitride(CBN) is a superhard materials with many advantages and many uses. Vitrified bond CBN grinding tool is a promising abrasive tool of high performance used for high speed, high efficiency, high precision grinding with lower grinding cost and less environment pollution. Sintering of vitrified bond CBN grinding tool was investigated in this paper. The results showed that practical sintering temperature of this tool was much lower than the initial oxidation temperature of CBN particle measured by comprehensive thermal analysis. The upper limit of sintering temperature should be determined by taking account of the thermal analyzing results, heating process of CBN and its change in strength and structure. Within the sintering temperature range of the vitrified bond, relatively higher sintering temperature was beneficial to the strength of bond bridge and the holding strength between bond and CBN abrasive particles. CBN tool sintered at relatively lower temperature tended to fracture through the bond bridge, while the one sintered at higher temperature tended to fracture along the boundary between CBN abrasive grain and vitrified bond.

Abstract: Electroplated CBN grinding wheels are not normally trued on a grinding machine and therefore inherently have a degree of run-out. The effect of run-out on workpiece roundness has both been modelled and measured experimentally. As well as affecting roundness, run-out can result in intermittent grinding around the wheel periphery, which can then lead to preferential wear on the most eccentric part of the wheel. This intermittent effect has been investigated by modelling the variation of the normal grinding force around the wheel and by measuring the variation of acoustic emission around the wheel during grinding tests.

Abstract: The paper presents results of investigations on the application of glass-ceramic to bonding the CBN grains into abrasive composite. The application of the glass with specific chemical composition makes it possible to generate the designed crystalline phase in it. A type of crystalline phase has a significant influence on the elastic modulus E.

Abstract: Al-cBN cermets have been hot pressed at temperature between 800oC and 1100oC and pressure of 50MPa in vacuum. The effect of particle size of the starting powders as well as the effect of starting compositions and temperature was investigated. The materials could only densify up to 84-92% of theoretical density. After hot pressing at 800oC only Al and cBN could be observed by XRD, whereas higher hot pressing temperature result in the formation of AlN and AlB2 which retard the densification. The microstructure of the hot pressed material was studied using scanning electron microscopy. It was observed that oxide layers exist at the interface between Al and cBN phases. The presence of these oxide layers resulted in blocking the Al from spreading and therefore preventing full densification.

Abstract: High-purity, single-phase polycrystalline diamond and cBN have been successfully synthesized by direct conversion sintering from graphite and hBN, respectively, under static high pressure and high temperature. The high-purity polycrystalline diamond synthesized directly from graphite at ≧15 GPa and 2300-2500 °C has a mixed texture of a homogeneous fine structure (grain size : 10-30 nm, formed in a diffusion process) and a lamellar structure (formed in a martensitic process). The polycrystalline diamond has very high hardness equivalent to or even higher than that of diamond crystal. The high-purity polycrystalline cBN synthesized from high-purity hBN at 7.7 GPa and 2300 °C consists of homogeneous fine-grained particles (<0.5 μm, formed in a diffusion process). The hardness of the fine-grained high-purity polycrystalline cBN is obviously higher than that of single-crystal cBN. The fine microstructure features without any secondary phases and extremely high hardness of the nano-polycrystalline diamond and the fine-grained polycrystalline cBN are promising for applications in next-generation high-precision and high-efficiency cutting tools.

Abstract: In the paper, a new technology combining conventional CBN electroplating and thermal diffusion in vacuum to produce gear-honing-tool for hardened tooth is introduced. The two factors, such as planting CBN abrasives and combination between electroplating layer and matrix that can affect the quality of gear-honing-tool, are investigated. Experiments show that using suspension CBN abrasive electroplating combined with thermal diffusion in vacuum can ensure the quality of planting CBN abrasives of gear-honing-tool and obtain the semi-metallurgy binding layer between CBN abrasives and matrix that withstands the force of honing gears.

Abstract: Wheel structure has a critical influence on grinding performance especially active cuttingedge density. Experiments were carried out to find out the relationshipbetween active and staticcutting edge density. It was found that there are many more active cutting edges in grinding thanexpected based on chip thickness formulae mainly due to wheel deflection in grinding.

Abstract: In this work cBN-TiN composites were studied. The composites were prepared by the HPHT technique (p=8 GPa, T=1750 0C). A TiN binding phase was used in two forms: as micro and nanomaterials. Thermodynamic calculations showed that formation of new phases in the cBNTiN composites was not possible in the experimental conditions which was confirmed by XRD investigations carried out. The surface morphology of nanocomposites was studied by scanning electron microscopy. The structure of these composites was compact; a TiN phase was uniformly distributed between cBN grains. Hardness was measured by the Vickers method using an indentation load of 9.81 N. The hardness of the investigated samples was dependent on the volume and grain size of the binding phase. Young's modulus of elasticity was determined, but its value was found to be dependent on the grain size of the TiN phase.