I. V. Uvarova

Manufacture of composite electrophoretic coatings using very finely divided Mo and Mo2C powders

An electroplating-electrophoretic procedure for producing composite coatings using a combination of electroplating and electrophoretic methods, followed by liquid phase sintering at the eutectic formation temperatures, has been studied. Finely divided Mo and Mo2C powders produced by low-temperature catalytic reduction of molybdenum trioxide and subsequent molybdenum carbiding were employed, and the main electrophoretic deposition mechanisms have been estabished. Electrophoresis parameters have been examined in terms of their effect on the precipitates formation rate and their structure. This procedure enables components operating under corrosion-erosion wear conditions to be protected and their service life increased by a four or fivefold factor.

Mechanosynthesis of Nanodispersed Titanium Diboride

Structural and morphological changes of titanium during intensive milling of titanium and boron powder mixtures in an AIR-015M planetary-ball mill are investigated. It is shown that the structural transformations in titanium lead to the formation of cluster precipitates (like Guinier–Preston zones) of titanium and boron atoms that are regularly oriented with respect to the titanium lattice and coherently associated with it. Cluster precipitates are very effective nuclei for the further reaction and provide an explosive transition to the almost single-phase titanium diboride. It was found that, in the investigated mechanosynthesis conditions, nanostructured titanium diboride forms in the form of flat and spatial polycrystalline particles, composed of oriented nanograins no larger than 20 nm.

Synthesis and Properties of Si-Modified Biogenic Hydroxyapatite Ceramics

The paper examines the production of Si-modified biogenic hydroxyapatite ceramics. The introduction of methylsilicic acid hydrogel in amounts converted to 2 and 5 wt.% Si and subsequent sintering at 600°C increase the specific surface area by 10 times, from 6.1 to 59.8 m2/g. The porosity of ceramics increases from 43.0 to 62.3% when the modifying addition reaches up to 5 wt.%, the compressive strength being equal to 27–33 MPa. The modifying addition also influences the structure and reduces the minimum grain size of the material from 0.65 to 0.1μm

Mechanical activation of the reactive sintering of titanium carbide

This paper describes the mechanical alloying of Ti and C powders by intensive grinding in a planetary mill. The effect of milling conditions and initial composition on the compositional homogeneity and properties of powders and samples consolidated by hot-pressing was studied by x-ray diffraction, scanning electron microscopy, and surface area measurement. The diffraction patterns indicated that a powder mixture ground for 24 hours transforms to TiC after sintering for only one minute at 600°C under a pressure of 3 GPa.

Formation of Diborides of Groups IV–VI Transition Metals During Mechanochemical Synthesis

Fine powders of diborides of groups IV–VI transition metals (TiB2, HfB2, NbB2, TaB2, CrB2, Mo2B5, and W2B5) were produced by mechanochemical synthesis and low-temperature heat treatment of activated charges. The particle size of the powders was ≤1 μm. It is revealed that processes of formation of diborides of groups IV–VI transition metals differ within period and group. Diborides Ti and Nb formed discontinuously. Diborides Hf and Ta formed after the formation of lower boride phases, whereas higher borides Cr, Mo, and W formed in almost a single-phase state only after a low-temperature treatment of preliminarily mechanoactivated charges. The differences were analyzed from the point of view of the donor-acceptor capacity of the atoms of boron and diboride-forming transition metals.

Combined Functional Biocoatings on the VT-6 Alloy

Electrochemical oxidation of spark-deposited coatings from intermetallic TiAl3 and TiN–3AlN nitride ceramics in 3% NaCl solution leads to a nanosized surface layer composed of titanium oxides of various composition: from higher to lower oxides toward the substrate. The highest corrosion resistance is shown by the intermetallic coating, which is confirmed by anodic oxidation polarization curves and layerwise Auger spectroscopy of protective titanium and aluminum oxide films. A combined biocoating is produced as follows: electrospark deposition of TiAl3 layer onto VT-6 alloy—electrochemical oxidation in 3% NaCl solution—deposition of hydroxyapatite layer—laser fusion. Energy-dispersive X-ray spectroscopy has revealed a wide adhesion area at the interface between the spark-deposited coating and hydroxyapatite, which agrees with smooth variation in microhardness in this area. The coating shows strong adhesion to the substrate and biocompatibility with the bone tissue.

Diffusion Chromizing of Molybdenum-Based Plasma Coatings

Thermochemical treatment (chromizing) of compacted steel parts on molybdenum-based plasma coatings was studied. The effect of heat treatment parameters on the structure and size of parts was examined. The sintering and diffusion hardening are recommended to be combined into one stage to simplify the production process and improve the performances of parts.

Use of Binary Titanium–Chromium Diboride for Producing Protective Coatings on a Nickel Substrate

The production of composite electrolytic coatings on a nickel substrate using binary titanium–chromium diboride obtained by mechanical synthesis was studied. The influence of heat treatment parameters on the phase composition and structure of the coatings was examined. It is shown that these coatings substantially increase the wear resistance of structural medium-carbon steel.

Physicochemical Stability of Hydroxyapatite–Low-Molecular Polyethylene Glycol 400 Composite Systems in Biological Media

The physicochemical stability of the composite system consisting of hydroxyapatite (HAP) including 10, 25, and 50% polyethylene glycol (PEG) with a molecular weight of 400 in different physiological solutions has been studied. In the interaction of HAP + PEG 400 composite systems with physiological solutions, the amount of Ca in the filtrate changes versus the PEG content of the composite and the salt composition of the reaction media. The rate of calcium release in Ringer and Ringer–Lokk solutions, whose chemical composition is close to that of the tissue fluid of living organisms, is almost twice as high as in a 0.9% NaCl solution. Chemical analysis has shown that the HAP +10% PEG 400 composite system interacts with physiological solutions and is likely to promote calcium interchange between the experimental material and tissue fluid. Infrared spectroscopy has demonstrated that polyethylene glycol is present in the HAP + 10% PEG system over 120 h of interaction with biological media of living organisms, which will promote the restoration of nervous impulses in the treatment of bone defects. The HAP + 10% PEG 400 composite system can be recommended for further study in the development of novel composite materials for rehabilitation orthopedics.

Highly Dispersed Powders in Boride–Silicide Systems

Nanosized composite powders with a composition of titanium diboride–silicides of group IV–VI transition metals are obtained in boride–silicide systems by mechanochemical synthesis for 5–30 min. The initiation effect of TiB2 on the formation of silicide phases during joint mechanochemical synthesis is shown. It is established that the powder particles are 40–70 nm in size. The powders tend to agglomerating. The properties of hot-pressed compacted TiB2–20 wt.% MoSi2 samples are studied: ultimate bending strength 421 ± 29 MPa; microhardness 25 ± 0.8 GPa. Electrolytic Ni–TiB2–MoSi2 coating possesses high wear-resistance in sliding friction and can be recommended for hardening and recovering the surfaces of machinery and mechanical parts.