Том 41, № 3 (2019)

Microcrystalline diamond powders are deposited directly by a HFCVD apparatus with adding amounts of trimethyl borate in gas mixture. The study establishes the relationship between the boron concentration and growth behaviors of microcrystalline diamond particles. The results present that the addition of boron and oxygen atoms increases the growth rate of diamond crystals by a factor of 1.2–1.7, moreover, does not influence the morphology and grain density of diamond particles significantly.

The present study investigated the effect of the temperature, at which a new matrix material was produced via hot isostatic pressing (HIP) method by adding certain rate of Co and Ni elements into CuSn (85/15) bronze alloy, and Co and Ni elements wear resistance of the samples produced. One of major advantages of HIP method is that heat and pressure are applied simultaneously during the sintering process. Thus, all or almost all of the pores are eliminated during the manufacturing and a denser material is obtained. During the study, sintering pressure and sintering time were kept constant as 15 min, and also sintering temperature was selected to be 700 and 800°C as the variable parameter. Sintering process was carried out under vacuum starting from the first burn. The produced samples were then prepared metallographically and SEM and EDS analyses were performed for microstructure examinations. Microhardness of the samples was taken to investigate mechanical behaviors of the samples and they were subjected to wear test. Finally, density test was applied to samples and their experimental and theoretical densities were calculated. In conclusion, it was seen that more homogenous samples were obtained as sintering temperature increased. As Co amount and temperature increased in the study, wear resistance increased.

Established were the regularities of variations of the temperature, cutting tool force and roughness of the machined surface for different cutting rates at the precision turning of aluminium and brass alloys using a cutter with the diamond-hard alloy plate.

Distribution characterization of geometry shape and size of abrasive grits with high quality in tight size band and exact pattern is crucial for modern tool manufacturer to make fine powder abrasive tool and other powder tools, but complex to be classified and evaluated accurately due to the lack of scientific method. In contrast to industrial methods with sieving mesh size or simplified projection criteria with circumscribed (inscribed or escribed) circle or rectangle, a set of new systemic criteria is developed and validated by measuring three representative grits samples in micron scale under 2D/3D microscopy platform. The features of micron abrasive grits under morphology classification include total four groups, six subgroups and eighteen sub-types in consideration of spatial geometry and statistical size distribution. For grinding performance analysis and simulation, it would be better to use a set of dominant volumetric geometries rather than use single simple geometry. Furthermore, the significance of abrasive grits geometries in grinding performance is discussed.

Presented are the results of the investigations of the structure and mechanical properties of consolidated MgB₂-based superconducting materials produced under high pressures and temperatures and hot pressing. It is established that the formations of inclusions of higher borides of phases with stoichiometry, close to MgB₁₂, considerably influenced on the level of the density of a critical current and mechanical properties of superconductive materials, in particular, leads to increase of the microhardness. The presence of additions of the Ti and SiC (10%), which positively influences the level of superconducting properties, accompanies by the change of mechanical properties, which are testify to the influence of the additions on the formations of MgB₁₂ inclusions.