Vol 55, No 6 (2019)

The results of experimental and theoretical studies of the creation of experimental and calculation methods are presented for the determination of the value of a distributed external load, which affects a wire during electrical discharge machining of certain groups of steel and hard alloys. The reliability of the results and the working efficiency of the obtained equations and models are supported experimentally. Their application in the technological process of design allows the true shape of the wire electrode to be calculated, which makes it possible to develop machining technology and the relevant patterns of motion of machine drives.

In the present work, a new type of wear-resistant coatings obtained on steels by contactless electro-spark deposition using a rotating electrode and by electrical discharge deposition with a vibrating electrode has been studied. Electrodes have been obtained by pressing and sintering multi-component powder mixtures of hard metal WC-Co with additives of super-hard and refractory compounds of B₄C and TiB₂ and semi-self-fluxing alloys Ni-Cr-B-Si. High density coatings, with a thickness up to 80 μm and micro hardness up to 17.0 GPa, have been obtained. The roughness, thickness, composition, and structure of the coatings thus obtained have been studied by X-ray diffraction, scanning electron microscopy, and electro-spark deposition. The influence of micro-geometric parameters, composition and structure of coatings on their tribological properties and wear resistance were studied by comparative tests of friction and abrasion wear. The friction tests showed that the wear of the coated steel surfaces is up to 5 times lower compared to the uncoated those. On the base of the experimental data, a comparative analysis of the coatings obtained by the two methods have been made. Appropriate regimes and conditions for deposition of coatings with optimal properties have been defined.

A composite material (DTD) consisting of titanium dioxide (TiO₂) nanoparticles deposited into the diatomite matrix is synthesized by a modified method based on the heterogeneous hydrolysis of titanium tetrachloride as a TiO₂ precursor. The initially prepared DTD samples are annealed at temperatures of 200 to 1000°C. The structure of resulting composite materials and TiO₂ nanoparticles residing on the surface are investigated by X-ray powder diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), X-ray energy-dispersive spectroscopy (EDS), Fourier-transform IR spectroscopy, and low-temperature nitrogen adsorption. It is shown that the TiO₂ deposited into the diatomite matrix exists in the anatase form and mainly lines the walls of macropores. The thermal stability of the prepared composites is studied, and it is found that, as the annealing temperature is raised, the size of TiO₂ nanoparticles increases, while the specific surface area and sorption pore volume diminish due to densification of the mesoporous structure of diatomite. The mesoporous structure exists to temperatures as high as 800°C, meaning that the thermal stability is improved compared to initial diatomite. The diatomite matrix in its turn improves the thermal stability of TiO₂ crystals and inhibits the anatase-to-rutile phase transition. The samples consisted of only anatase phase (i.e., no rutile is formed) up to 800°C. Annealed at 1000°C, the composites lose their porous structure and contain a mixture of crystalline anatase and rutile nanoparticles with a mean diameter of 5 to 10 nm.

Polyethylene (PE) composites containing montmorillonite are studied. The incorporation of nanoparticulate montmorillonite into the polymer is shown to affect its electret, electric, and rheological properties. We find that the observed enhancement in the electret properties of PE samples containing 2 or 4 vol % of the filler is related to changes in the chemical structure (namely, oxygen-containing functional groups are formed in PE macromolecules as a result of mechanochemical destruction) and the electric and dielectric properties of PE itself, but the emergence of new type of traps for injected charge carriers at the polymer−filler interface has a greater contribution to the observed effect.

In the design of a working operation with a multicriteria estimation of results a stage in the procedure is selecting technology regulations for the implementation. A modified optimization algorithm is proposed that simplifies the content of the factor space by eliminating critical values in searching for an optimum processing mode. The influence of these values is compensated by changing the strategy of the working operation, in particular, by using the method of fitting the critical index to the required level with a decreasing controlled increment of the value. To implement various operations with an adaptive form of their organization (precision hole machining, formation of dimensional slits, and surface heating with a normalized depth of the zone), a number of process installations and devices have been developed, whose circuits are presented in this work. Their application improves the reproducibility of the processing results in the case of a simplified procedure for selecting the regulations by which the technology is operated.

Corrosion inhibition performance of 5-(3-Pryridyl)-4H-1,2,4-triazole-3-thiol on aluminium alloy AA6061 in 0.1 M HCl solution was tested by the weight loss method, potentiodynamic polarization and electrochemical impedance spectroscopy. The effect of an increase in temperature and a change in the concentration of the inhibitor were studied. The results indicated that with an increase in the concentration of the inhibitor and temperature the inhibition efficiency also increased. The inhibition efficiency as high as 94.1% was found at 60°C for 40 ppm of the inhibitor. By the perusal of thermodynamic and activation parameters, it is found that adsorption of the studied inhibitor takes place through chemisorption. The inhibitor agrees the Langmuir adsorption isotherm and acts as a mixed type inhibitor. Thermodynamic parameters also unveiled that the process of adsorption on the metal surface takes place through chemisorption. The formation of a protective film on the metal surface was confirmed by scanning electron microscopy. From the mechanism of corrosion inhibition, it is possible to deduce the formation of a coordination bond between the inhibitor and the metal surface. The inhibition nature of the molecule was explained by theoretical studies.