Vol 39, No 5 (2017)

The structures and mechanical properties of materials based on α-AlB12 without additives and with additions of carbon and titanium carbide sintered under high (2 GPa) pressure and by hot pressing (30 MPa) in the contact with hexagonal BN. The light materials were obtained having high hardness, fracture toughness, ultimate strengths at bending, R_bm, and compression. The addition of 17 wt % C to α-AlB₁₂ and sintering at 30 MPa makes possible to achieve fracture toughness K_Ic (49 N) = 5.9 ± 1.4 MPa·m^0.5, hardness H_V (49 N) = 23.6 ± 2.8 GPa, bending R_bm = 310 MPa and compression R_cs = 423 MPa strengths and specific weight was γ = 2.7 g/cm³. The addition of 20 wt % TiC to α-AlB₁₂ and sintering at 30 MPa resulted in the formation of AlB1₂C₂ and TiB₂, increase of the hardness H_V (49 N) = 28.9 ± 1.9 GPa, R_bm = 633 MPa, R_cs = 640 MPa and γ = 3.2 g/cm³, the K_Ic(49 N) = 5.2 ± 1.5 MPa·m^0.5.

The study of the kinetics of aluminum oxidation process in the presence of modified nanodiamonds and diamond-containing soot (DND-TAN and DCS-boron, respectively) shows their impact on the growth and quality of anodic films: the film thickness and the current efficiency have increased by 13 % at 2 A/dm² and using DCS-boron; the number of pores has been reduced two-fold using nanodiamond additives; no pinholing has been detected; micro-hardness of the oxide coating has increased 1.5 to 1.6 times (up to 1020 kg/mm²).

Physicochemical characteristics of carbon nanotubes synthesized on Co₂O₃ and oxide Cu–Co–Fe catalysts on their base applied in the CO oxidation reaction have been investigated. It is shown that the deposition technology of the active mass, which, according to the X-ray phase analysis, is a mixture of the Cu₂(OH)₃NO₃ and CuO phases, strongly influences the activity of the Cu–Co–Fe/CNT catalysts. The greatest amount of the Cu₂(OH)₃NO₃ phase is observed in the catalysts produced by a single deposition of the active component on carbon nanotubes, which according to the thermodesorption mass spectroscopy, contributes to the formation of active centers with the lower activation energy of the CO₂ desorption and the reaction of the CO oxidation proceeds at a considerably lower temperatures. The TEMdata indicate that at the step-by-step deposition of the active mass in the surface layer the formation of the massive agglomerates, which are inhomogeneously located on the disordered structures of nanotubes, and this unfavourably affects the catalytic properties of Cu–Co–Fe/CNT catalysts.

Mechanical and tribotechnical characteristics of composite multilayered coatings Zr–ZrN in air at temperatures from 20 to 900°C have been determined. The coefficient of friction of the Zr–ZrN coating against steel 65G has been found to exhibit a tendency toward decreasing as the velocity is lowered and the load is raised from 10 to 30 kgf. A study of properties of the coatings in the range between 20 and 900°C has demonstrated that hardness under a load of 1 kgf goes down gradually from 19 to 3.2 GPa. Hardness along the friction trace has been found to grow from 23 to 25 MPa, while hardness of the counterbody has increased twofold (from 4.5 to 9.0 GPa). The coefficient of friction of the composite multilayered coating Zr–ZrN against diamond at a velocity of 16 mm/s has been determined to range between 0.26 and 0.28.

In this paper, a nano-scratch testing approach was used to measure and evaluate the abrasion wear resistance of high-chromium white cast irons in order to understand the wear mechanism in the interaction between the high-chromium white cast iron and the cBN cutting tool during the machining process. Scratch testing was performed on a nanoindentation instrument using a diamond indenter as the scratch tool. Linear multi-pass scratches in the same path were made on pre-worn surfaces of test materials. The correlation of the scratching resistance and tool wear measured from the machining is presented by the flank wear and maximum scratch depth. The appearance of the cutting edge on a cBN tool suggests that the abrasion wear is mainly related with a combined effect of the carbides and the matrix during machining the high-chromium white cast iron.