Vol 39, No 1 (2017)

Application of diamond is determined by its oxidation behaviour in some measure. Oxidation process of single-crystal diamond prepared under high pressure and high temperature (HPHT) has been studied by the thermal analysis, scanning electron microscope (SEM) and Raman spectrometer. The result of a simultaneous thermal analysis indicates that single-crystal diamond is oxidized at ~ 818°C at a heating rate of 5°C/min in the flowing oxygen. Based on the data of the thermal analysis at different heating rates, the activation energy is calculated by the Kissinger method. A weight loss rate increases with the rising heat treatment temperature from 600 to 800°C. After the oxidation at 800°C, etch pits emerge on the {100} surfaces of single-crystal diamond, while the {111} surfaces are smooth. Shapes of the etch pits on the {100} surfaces are inverted pyramidal hollows, with edges direction parallel to the <110> direction.

The corrosion resistance of titanium-chromium-diboride-based ceramic materials and cermets in 3% NaCl solution (to simulate sea water) is studied by the method of potentiodynamic polarization curves. The composition and microstructure of oxidized specimen surfaces are examined. Adding small amounts of AlN (5 to 10 vol %) to TiCrB₂ provides an essential improvement of the corrosion resistance. Introduction of an NiAlCr metallic binder into the material composition results in a lower resistance to anodic oxidation.

In this paper the thermal properties of diamond composites with ceramic bonding phases, such as the Ti–Si–C system with nanometric Ti(CN) and TiB₂ are presented. The thermal conductivities of the materials were analyzed by the laser pulse method. In addition, computational simulations of the temperature dependence on the distance from the cutting edge were performed according to the finite element method for the investigated composites, commercial PCD, and hypothetical diamond monocrystal. Two cutting speeds were considered during the numeric computations: 100 and 200 m/min. To verify the simulations, the TNGA 160408 cutting insert, which was prepared from the investigated diamond composites and commercial material, was employed. Dry turning tests of titanium alloy were conducted. The temperatures during the machining processes were observed using a thermovision camera, and the surface roughness was measured after the tests. The computational simulations confirmed the strong dependence between the thermal properties of the cutting material and the temperatures within the cutting zone. The temperature measurements during the dry cutting tests reveal significantly higher temperatures than the temperature measurements achieved during the simulations.

Compressibility of boron subphosphide B₁₂P₂ has been studied under quasi-hydrostatic conditions up to 26 GPa and 2600 K using laser-heated diamond anvil cell and angle-dispersive synchrotron X-ray diffraction. 300-K data fit yields the values of bulk modulus B₀ = 192(11) GPa and its first pressure derivative B₀′ = 5.5(12). It has been found that at ambient pressure the thermal expansion is quasi-linear up to 1300 K with average volume expansion coefficient α = 17.4(1) × 10⁻⁶ K⁻¹. The whole set of experimental p–V–T data is well described by the Anderson-Grüneisen model with δ_T = 6.