M. G. Kovaleva

Effect of vacuum annealing on tribological behavior of nanosized diamond-like carbon coatings produced by pulse vacuum-arc method

Results of tribotests of nanosized carbon coatings formed on silicon surfaces by the pulse vacuum-arc method at various orientations of substrates with regard to a carbon plasma flow are presented; the tribotests were carried out for as-deposited coatings and coatings annealed in vacuum at 600 and 800°C. It has been shown that, among as-deposited coatings, the carbon coating deposited on a substrate perpendicular to the axis of the plasma flow has the highest wear resistance. An increase in the wear resistance of diamond-like carbon coatings after annealing at 600°C has been found.

Structure and properties of an Al2O3 powder coating formed by a cumulative detonation method

The strength of the Al2O3 powder coating formed by a cumulative detonation method on a steel St3 substrate is determined, and its structure is studied. The optimum conditions for deposition are chosen. They make it possible to form a dense high-strength coating with good adhesion to the substrate.

Properties, Peculiarities and Applications of Powder Coatings Formed by Multi-Chamber Detonation Sprayer

The paper describes the properties of Ti, Nickel-based, and Al2O3 powder coatings obtained through a new method of powder acceleration which allows to achieve the powder velocity of 1400m/s. The Ti-based coatings thus formed have nanocrystal and amorphous structure with nanodispersed ceramic compounds inclusions, and show the hardness of up to 16GPa, high plasticity and adhesion strength. The Nickel-based alloy coatings display both nanocrystal and amorphous structure. In ceramic Al2O3 coatings high spraying velocity allows filling in the space between the deformed oxide particles (about 0.053 microns in size) by nanocrystal and amorphous phases; thus, the coatings acquire a high degree of plasticity retaining high hardness of 1320 HV0.3 with the porosity below 0.5%. The Al2O3 coatings were tested and found effective for covering the surface of porous metal matrixes in burners.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALUMINA POWDER COATINGS BY A NEW MULTI-CHAMBER DETONATION SPRAYER

The dense ceramic coatings based on alumina with hardness of 1100±25 HV0.3 and porosity of less than 1% have been prepared by multi-chamber detonation sprayer (MCDS) with a barrel length of 500mm. The intermetallic compound of type FeAl was revealed in the area of the coating that adjoins the substrate.

Synthesis of Magnesium Oxide Nanopowder by Thermal Plasma Using Magnesium Nitrate Hexahydrate

Magnesium oxide (MgO) nanopowder was synthesized by thermal plasma in a novel thermal DC plasma torch using magnesium nitrate hexahydrate. Magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) was obtained from serpentinite (Mg3Si2O5(OH)4; lizardite) (Halilovskiy array, Orenburg region, Russia). The synthesized samples were characterized by analytical techniques including X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM characterization studies confirmed that MgO nanopowder obtained has periclase structure with high purity, and the particle sizes vary within the range of 100 nm to 150 nm. We believe that the present work will promote further experimental studies on the physical properties and the applications of MgO nanopowders in the fields such as high-densed ceramics, additives in bactericide, and refractory products.

Properties and Peculiarities of WCCoCr Coatings Formed by Multi-Chamber Detonation Sprayer

Multi-chamber detonation sprayer (MCDS) was applied for deposition of WC-Co-Cr powder coatings on corrosion-resistant steel. Powder AMPERIT®554.074 WC-Co-Cr was used to deposit of a coatings. The coatings microstructures and phase compositions were characterized using SEM, OM and XRD techniques. Measurement of the microhardness of samples was done with a micro-hardness tester DM – 8B using a Vickers’s indenter with load on of 0.3 N. It was established that MCDS has provided the conditions for formation of a dense layer with porosity of less than 1.5 % and microhardness 750±50 HV0.3.

Effect of the surface modification of titanium nickelide by nitrogen and titanium ions on the adhesion to a nanosized carbon coating deposited by a pulsed vacuum-arc method

The adhesion strength of nanosized carbon coatings deposited by a pulsed vacuum-arc method to the titanium nickelide substrate preliminarily modified by the irradiation of nitrogen and titanium ions is studied. Preliminary modification of the titanium nickelide surface is found to prevent the swelling and exfoliation of a carbon coating.

Properties of Coatings Based on Carbon and Nitrogen-Doped Carbon Obtained Using a Pulsed Vacuum Arc Method

Diamond-like carbon coatings on hard-alloy substrates, including coatings doped with nitrogen about 1.0 μm thick have been obtained using a pulse vacuum-arc method. Three types of coatings have been investigated: a carbon diamond-like coating (C), a carbon coating doped with nitrogen (C: N), and a composite coating based on (C: N + C) layers. The coatings have been annealed in atmospheric air at a temperature of 400°C. The tribological characteristics (wear resistance and friction coefficient change dynamics), the adhesion strength, and the microhardness of coatings in the initial state and after annealing have been studied. The composite coating consisting of C: N + C layers surpasses the constituent coatings in properties, both in the initial state and after annealing at a temperature of 400°C.

Structure and Mechanical Properties of TiAlSiY Vacuum-Arc Coatings Deposited in Nitrogen Atmosphere

The effect of a negative bias potential applied to the substrate on elemental composition, structure, and mechanical properties of vacuum-arc TiAlSiY nitride coatings is investigated by different methods. It is ascertained that applying a high (up to–500 V) bias voltage leads to a selective sputtering of target as well as significant microdeformation of the coating, small-sized growth of crystallites, and their preferred orientation along the [110] direction. In this case, the coating deposited has a low hardness H = 6.95 GPa and propensity to intense wear under scratch and tribological tests. Crystallites with stoichiometric composition ~140 nm in size and [111] preferred orientation perpendicular to the surface of growth are formed at the bias potential about–200 V, and superhard (H = 49.5 GPa) and wear-resistant coatings are grown under such conditions. The mechanisms of formation of the structure of multielement coatings are discussed. It is shown that formation of an amorphous phase and nanocrystal [110] texture takes place at a high bias potential owing to the process of radiation-stimulated selective spraying of the target. Formation of microstrained crystallites 10 nm in size caused by the weakening of interatomic bonds is observed in the coating under such deposition conditions, and it leads to the decrease in coating hardness and fast destruction during tribological testing. Substantial bias voltage dependence of deposited coating properties is established in our investigations.

Properties of Coatings on the Basis of Carbon, Tungsten, Boron, and Titanium Obtained by the Pulsed Vacuum-Arc Method

Results of an investigation of the properties of coatings on the basis of carbon, tungsten, boron, and titanium obtained by the pulsed vacuum-arc method are presented. It has been found that the adhesion characteristics of coatings based on boron and titanium may be improved using a composite carbon-based coating, doped with tungsten, boron, and titanium, which, moreover, has a microhardness greater than those of a coating based on titanium and boron.