Papers by Keyword: Superhard Material

Abstract: In this thesis, elastic properties of three BCN superhard materials with different structures are computed by using CASTEP software developed according to the first principles which are based on density functional theory (DFT) and plane wave method. CA-PZ of local density approximation (LDA) and PBE of generalized gradient approximation (GGA) are adopted to describe the exchange-correlation effect between electrons. The results are compared with other findings and c-BN data. Through analysis, it is found that the spatial anisotropy do exist in the Young's modulus of single crystals all three BCN compounds.

Abstract: Diamond-like B-C-N compounds have the excellent potential properties like diamond or cubic boron nitride. In this paper, diamond-like B₂(CN)₃ compound has been studied by first principle calculations. After geometry optimization, hexagonal and monoclinic B₂(CN)₃ models were obtained. According to the band structure and density of state calculated, they are conducting. The relative stability was proved using elastic constants calculated by Born criterion. The monoclinic B₂(CN)₃ is one of hard material with theoretical Vickers hardness 38 GPa.

Abstract: Boron carbide-based materials B4C-MexBy were densified by pressureless sintering in a vacuum furnace. Some transition metal carbides (TiC, ZrC, HfC, Cr3C2 and WC) from groups IV-VI were used as sintering aids. The optimal sintering temperature in the range 2220-2250oC was used for any composition. Here we show the possibilities to activate the mass transport of the B4C by the mechanism of liquid phase sintering. The method of reactive sintering of B4C in the presence of additives of some transition metal carbides allows in situ synthesis of dense B4C-MexBy materials. Structural properties and fracture toughness of the B4C-based composite materials were discussed. The properties of some of these materials and the possibilities for their application are also discussed.

Abstract: The recent attempts to design new super- and ultrahard materials concentrate predominantly on those with high elastic moduli. This approach neglects the fact that elastic moduli describe the reversible, elastic response to small strain near equilibrium, whereas hardness is related to plastic deformation, the measurement of which involves substantial plastic strain, where the electronic structure becomes strongly distorted and can often result in structural transformations to softer phases. In the superhard nanocomposites consisting of 3-4 nm size randomly oriented nanocrystals of hard transition metal nitrides joined together by about one monolayer of silicon nitride variant, which is strengthened by negative charge transfer, the nanocrystals are free of defects and therefore reach ideal strength. Because of the strengthening of the interface and of the random orientation of the nanocrystals, these nanocomposites reach hardness of more than 100 GPa as shown experimentally. We provide a simple theoretical explanation why these materials can exceed the hardness of diamond, and outline a possible way how to design new nanocomposites with even higher hardness when reduction of Friedel oscillations of the valence charge density, which weaken the strength of the transition metal nitride, can be accomplished.

Abstract: In order to further improve machining quality of superhard materials, it was presented that adds a squeeze film damper on the wheel spindle of ultrahigh speed grinder as a assistant elastic sustain to attenuate the vibration of the wheel spindle. Work principle of squeeze film damper was analyzed; the squeeze film pressure distribution was researched through simulation and damper parameters effect on damping coefficient was studied. Base on the theory research the damper was designed and experiments was done. Experimental result shows the amplitude of the grinding wheel spindle can be reduced 20% and machining quality of superhard materials can be improved 10%～20%. Research works provides a new method for superhard materials machining.

Abstract: In modern industry time, more strict requirement on dimension precision, geometry shape and surface roughness of holes have been set to meet the continue advent of superhard materials, the interchanges requirement under batch production, and the application of precision and super-precision machining technique. The super hard material precision reamers have great advantages in dealing with these problems. This paper presents a new process in designing and manufacturing of the superhard material precision reamers, which is called inside-holding electroplating technique. The new process adopts inside-holding electroplating process, eddy flowage electroplating device, extracting pattern process and etc.. Comparing with traditional process, the new one has such advantages as low production cost, high precision, long service life, undressed, and so on.