Katsuko Harano

Ultrahard diamond indenter prepared from nanopolycrystalline diamond.

Knoop indenters were prepared from nanopolycrystalline diamonds (NPDs) synthesized by direct conversion sintering from graphite under high pressure and high temperature. Owing to the fine structure (grain size: 10-100 nm) of NPD, high-accuracy sharp edges could be formed at the indenter tips. The indentation tests demonstrated that the NPD indenter can form normal (measurable) indentations on NPD samples without fracture or chipping even at high temperatures of up to 1000 degrees C, while conventional indenters made of single-crystal diamonds break easily above 600 degrees C. This suggests that the NPD indenter has greater potential in high-temperature hardness tests than the conventional single-crystal diamond indenters.

Optical Characteristics of Nano-Polycrystalline Diamond Synthesized Directly from Graphite under High Pressure and High Temperature

Optical properties of nano-polycrystalline diamond (NPD) synthesized by direct conversion from high-purity graphite under high pressure and temperature were investigated by infrared (IR), ultraviolet (UV), and photoluminescence (PL) spectroscopy. IR spectroscopy revealed that NPD has no large lattice strain and very few impurities, but possesses an absorption band attributed to a trace of hexagonal diamond. UV spectra displayed a continuous absorption wing due to structural defects and secondary absorption edge attributed to electron transitions from aggregated nitrogen. PL spectra exhibited peaks of N3 centers and broad bands related to dislocations.

Performance of Newly Developed Single-Point Diamond Dresser in Terms of Cutting-Point Rake Angle

A cutting-tool-type single-point diamond dresser, the tip of which has a given rake angle, was developed and its dressing and grinding performances were investigated. It was found that the dressing mechanism changes its mode from a ductile mode to a brittle mode with increasing back rake angle in the negative direction and that the cutting-tool-type dresser exhibits good robustness owing to the fact that its ground surface roughness is not markedly affected by the dressing conditions.

Note: Evaluation of microfracture strength of diamond materials using nano-polycrystalline diamond spherical indenter

Ultra-hard and high-strength spherical indenters with high precision and sphericity were successfully prepared from nanopolycrystalline diamond (NPD) synthesized by direct conversion sintering from graphite under high pressure and high temperature. It was shown that highly accurate and stable microfracture strength tests can be performed on various super-hard diamond materials by using the NPD spherical indenters. It was also verified that this technique enables quantitative evaluation of the strength characteristics of single crystal diamonds and NPDs which have been quite difficult to evaluate.

Cutting Performances of Nano-Polycrystalline Diamond

Single-phase (binder-less) nano-polycrystalline diamond (NPD) has been synthesized by direct conversion sintering from graphite under high pressure and high temperature. NPD is characterized by extremely high hardness compared with single crystal diamond (SCD), even at high temperature. In addition, NPD has high wear resistance, no anisotropic mechanical properties, no cleavages, and high thermal stability. These characteristics suggest that NPD has high potential for use in precision cutting tools for various hard works. In order to evaluate the cutting performance of NPD, cutting tests for various cemented carbides were conducted under various conditions and the results compared with those of single crystal diamond (SCD) and conventional polycrystalline diamond containing metal binder (PCD). The results revealed that NPD has outstanding potential for precision cutting and processing of diverse hard and brittle materials.

Wear Characteristics of Various Diamond Tools in Cutting of Tungsten Carbide

Face cutting of tungsten carbide was conducted using two monocrystalline diamond tools and three polycrystalline diamond tools to investigate the wear characteristics in terms of the crystal structure and composition of the diamond. It was found that the wear of the monocrystalline diamond tool depends on the crystal planes that form the rake face and flank face of the cutting tool, and a cleavage fracture occurs when the cutting force acts as a shear force on the (111) crystal plane. The binderless nano-polycrystalline diamond tool exhibits excellent wear resistance beyond those of the sintered polycrystalline diamond tool and chemical vapour deposition polycrystalline diamond tool, as well as better wear resistance than the monocrystalline diamond tool.