Nanocomposites and nanomaterials

High quality cutting tools made from nanocomposite “diamond - tungsten carbide"
O.O. Bochechka, S.A. Klimenko, Т.О. Kuryljak, S.М. Nazarchuk, Ju.O. Melnijchuk, V.М. Тkach
V. Bakul Institute for Superhard Materials, Natl. Acad. of Sci. of Ukraine. Avtozavodska, 2, Kyiv-04074, Ukraine. 
E-mail: bochechka@ism.kiev.ua

It was found that in the presence of tungsten, the rate of oxidation of the diamond nanopowder decreases as a result of the chemical modification of the surface of diamond nanoparticles by tungsten - the formation of W–C bonds identified by IR spectroscopy.
To enhance the modification of the diamond nanoparticles surface by W–C bonds, ammonium tungstate (NH4)4W5O17 ×2.5H2O, soluble in water at elevated temperature, was used. The dissolved salt was used as a medium for preparing a mixture of diamond nanopowders and WO3. Intensification of the stirring process was carried out by the action of ultrasonic radiation. After drying, the mixture was heat-treated in a hydrogen atmosphere, degassed in vacuum, sintered in a high-pressure apparatus.
The above method of preparing the initial mixture improves the sintering of the diamond nanopowder of static synthesis. In the structure of the composite, sintered from this mixture for 20 s at a temperature of 1900 ° C and a pressure of 8 GPa, there are no sections in which agglomerates of diamond particles or tungsten compounds were present. The hardness of this composite under load 9.8 N on the Knoop indenter is 32 GPa, which is 1.2 times higher than the hardness of diamond-WC nanocomposites obtained without using a soluble tungsten-containing substance.
The cutting tool, equipped with manufactured samples of the composite, has a high working capacity when processing products made of aluminum-silicon alloys (such as AL25), silicified graphite, carbides. The roughness of the surface treated with diamond-WC composite cutters is Ra 0.35–0.80 depending on the material being processed and the cutting conditions. It is established that the created tools allow carrying out both unstressed processing and processing with dynamic loads during the turning of aluminum-silicon alloys products at high cutting speeds (500–700 m/min).  At high-performance turning (v = 30–40 m/min.) of carbide, the wear rate of tools from the developed composite is 30-35% lower compared to the tools equipped with diamond-carbide plates.