9:30 AM - 9:45 AM
[20a-H103-3] Boron-doped Nano-Polycrystalline Diamond: Development & Properties
Keywords:diamond,boron-doped,nanopolycrystal
For the first time, we developed binder-less boron-doped nano-polycrystalline diamond (B-NPD) by direct conversion of boron-doped graphite into nano-polycrystalline diamond under high pressure (16 GPa) and high temperature (2000 K). Grain sizes of B-NPD specimens were lower than 200 nm. Although, obtained grain sizes were related to the initial concentration of boron in the starting graphite, we have controlled grain sizes down to 40 nm. Grainsizes of B-NPD were estimated by XRD. XRD and Raman spectroscopy indicated that B-NPD is a bulk polycrystalline material without sp2 component which is commonly found in nano-crystalline films. Therefore, the hardness of B-NPD surmounted boron-doped nano-crystalline diamond films (NCD). We selectively synthesized B-NPDs, the boron concentration was in range from 0 ppm to 6000 ppm identified by secondary ion mass spectrometry measurements. The representative Knoop hardness of the B-NPD was around 125 GPa for B-NPD containing 300 ppm boron. This is comparable to that of conventional, non-doped, nano-polycrystalline diamond (NPD). B-NPDs containing 4000 ppm boron could be machined by an electro-discharge processing method. Because of the conductivity, B-NPD prevented microplasma effect which could be caused by tribocharging in a gap of sliding contact with insulating materials. In contrast, conventional, non-doped, NPD was damaged significantly by microplasma-caused wear. Single crystal diamond was also severely damaged by microplasma-caused wear. Beside this, the oxidation durability was improved. The mass of B-NPD started to be lost at around 1070 K whereas conventional NPD started to lose its mass at around 870 K in the atmospheric air. We regard this as a formation of boron oxides on the surface of the B-NPD. Beside this, tribological friction property was improved due to not only formation of lubricative boron-oxides but also non-charging property whereas electric charging often contributes to friction resistance.
Finally, we have prototyped some cutting tools made of B-NPD, the results of cutting tools indicated the B-NPD tools can be applied to alumina (Al2O3), quartz (SiO2). Furthermore, we have found that B-NPD is suitable for machining of polycarbonate which is a known difficult-to-cut material for diamond because of its electrostatically charging property. Besides, precision micro-tools with edge-line accuracy < 0.1 um and Ra = 30 nm were fabricated from B-NPD with 4000 ppm boron by electric discharge machining.
In summary, newly developed B-NPD has outstanding potential as a materials for high-performance and high-precision cutting tools, especially for applications regarding cutting tools for hard insulating materials and difficult-to-cut molded resins.
Finally, we have prototyped some cutting tools made of B-NPD, the results of cutting tools indicated the B-NPD tools can be applied to alumina (Al2O3), quartz (SiO2). Furthermore, we have found that B-NPD is suitable for machining of polycarbonate which is a known difficult-to-cut material for diamond because of its electrostatically charging property. Besides, precision micro-tools with edge-line accuracy < 0.1 um and Ra = 30 nm were fabricated from B-NPD with 4000 ppm boron by electric discharge machining.
In summary, newly developed B-NPD has outstanding potential as a materials for high-performance and high-precision cutting tools, especially for applications regarding cutting tools for hard insulating materials and difficult-to-cut molded resins.