Papers by Keyword: Nanopolycrystal

Abstract: Wear characteristics of binder-less (single-phase) nanopolycrystalline diamond (NPD) and cubic boron nitride (BL-PcBN) were investigated by rubbing them against various ceramics such as SiO₂, Si₃N₄, Al₂O₃ and SiC. The wear rates of NPD and BL-PcBN against SiO₂ and Si₃N₄ at high speed rubbing (280-360 m/min) at a loading pressure of 55 MPa (starting condition) were considerably high, indicating the main wear process is a chemical reaction. BL-PcBN specimens were found to be worn at much higher (more than ten times) rates than NPD, suggesting that cBN highly reacts with these ceramics in comparison with diamond under the experiment condition.

Abstract: Binder-less nanopolycrystalline cBN (BL-PcBN) synthesized by direct conversion under high pressure and high temperature has a fine texture consisting of small cBN grains (<100nm), high hardness (40–50 GPa) and high transverse rupture strength (1.3–1.6 GPa). Their mechanical properties strongly depend on their starting materials and synthetic conditions. In this study, Ball-end mill tools prepared from several kinds of BL-PcBN synthesized under various conditions (8–20 GPa, 1500–2300oC) were examined for precision cutting of high-strength hardened steel comparing with conventional sintered cBN. A fine mirror-finish surface with Ra of 20 nm could be produced by precision BL-PcBN tools, while not by conventional sintered cBN tools. The tool wear of BL-PcBN synthesized from hBN at 10 GPa and 2200°C was four to five times less than that of conventional cBN. These results revealed that the BL-PcBN tools have excellent potential for precision cutting on ferrous materials.

Abstract: Well-crystallized nanopolycrystalline thin films of cubic strontium titanate, SrTiO3, have been prepared on the TiNi-deposited Ni substrate in Sr(OH)2 aqueous solutions at temperatures between 130 and 200°C under saturated vapor pressures. The microstructure and morphology of the films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photoelectrochemical properties of SrTiO3 thin films on TiNi-deposited Ni substrate were investigated on a three-electrode assembly. The grain sizes increased from 30 nm to 300 nm and the relative crystal intensity in XRD pattern increased with the reaction temperature. Its photocurrent increasesdfirst with the grain size, then decreased. When the grain size of the film is about 200 nm, the photocurrent is highest.