Vladimir Koshuro

Superhard oxide coatings formed on titanium treated by high-frequency currents

We have studied the hardness and elastic modulus of rutile (TiO2) oxide coatings formed on the surface of commercial grade VT1-00 titanium treated by high-frequency current (HFC). The mechanism of formation of superhard oxide coatings with thicknesses within 2–3 μm and submicron-grained structure consisting of prismatic crystallites with dimensions of 200–400 nm. It is established that, at high temperatures (within 1000–1200°C) and short HFC treatment durations (30–300 s), the oxide coatings are characterized by hardnesses of about 61–78 GPa and elastic moduli within 330–680 GPa.

Morphology and microhardness of TiC coatings on titanium treated with high-frequency currents

The treatment with high frequency currents (HFC) is traditionally used to improve the mechanical properties of metal products, in particular hardness and wear resistance. A new method of carburization of titanium samples in a solid carburizer using HFC is proposed in the work. The temperature of the carburization is characterized by a wide range from 1000 to 1400 °C. As a result of thermochemical treatment, a hard coating of TiC (H ≥ 20 GPa) with a microstructure (d = 7-14 μm) consisting of nanoparticles (d = 10-12 nm) is formed on the titanium surface. These coatings are widely used in friction pairs for various purposes, including machinery, instrumentation and medicine.

Microstructure and hardness of carbon and tool steel quenched with high-frequency currents

In the course of high-temperature treatment with high-frequency currents (HFC) in the range from 600 to 1300 °C, carbon and tool steels are strengthened. After the heat treatment the hardness reaches 64-70 HRC for carbon steel (carbon content 0.4-0.5%) and 68-71 HRC for tool steel 1.3343 (R6M5 steel analogue with 0.9-1.0% C content, W – 5-6 wt%, Mo – 3.5-5.3 wt%, V – 1.3-1.8 wt%, Cr – 3.8-4.3 wt%, Mn+Si – 0.5-1 wt%, Fe – balance). The resulting structure is a carbide network, and in the case of tool steel – complex carbides around a high-strength martensitic phase.

The structure of Ti-Ta welded joint and microhardness distribution over the cross section

In order to create highly efficient medical systems and measuring biosensors, an approach is frequently used, in which the constructive basis of the product is made of a high-strength biocompatible material (titanium, stainless steel), and the functional layer is made of a more expensive metal (Ta, Zr, Au, Pt, etc.) or ceramics (Ta2O5, ZrO2, CaTiO3, etc.). For a strong connection, e.g. titanium with tantalum, it is proposed to use diffusion butt welding. The heat generated by passing electric current (I is not less than 1.95-2.05 kA, P – not less than 9 kW, t = 250-1000 ms) and applied pressure (30-50 MPa) ensure an integral connection. To improve the quality of the joint, i.e. to exclude cracks and tightness, it is necessary to choose the right combination of the thickness of the welded parts. It was established that when titanium (2 mm thick) and tantalum (0.1-0.5 mm) are combined, a better Ti-Ta welded joint is formed when tantalum foil is used (0.5 mm). Here the distribution of hardness over the cross section of the sample, including the welding areas, is uniform and has no extremely high residual stresses of the tensile type.

Surface morphology data of tantalum coatings obtained by electrospark alloying

The article presents the data of scanning electron microscopy of the surface morphology of tantalum coatings produced by electrospark alloying. To perform the statistical analysis of open porosity and morphological parameters of the coatings, raw digital images of the structure were studied. In this case, “AGPM” software for the analysis of geometric parameters of microobjects was used. When processing digital images of the surface morphology, open porosity, total quantity, average size and dispersion of the structural elements (particles and pores) were determined, and typical distribution patterns of structural elements were obtained from linear dimensions.

Peculiarities of structure formation of layered metal-oxide system Ti-Ta-(Ti,Ta)xOy during electro-spark alloying and thermally stimulated modification

The study focuses on high-performance combined electro-spark alloying of titanium and titanium alloy (VT1-0, VT16) surface and porous matrix structure oxidation. The metal-oxide coatings morphology is the result of melt drop transfer, heat treatment, and oxidation. The study establishes the influence of technological regimes of alloying and oxidation on morphological heterogeneity of biocompatible layered metal-oxide system Ti-Ta-(Ti,Ta)xOy. It was found that during electro-spark alloying the concentration of tantalum on the titanium surface ranges from 0.1 to 3.2 at.%. Morphology of the deposited splats is represented by uniformly grown crystals of titanium and tantalum oxides, which increase from nano- to submicron size.

Structural and chemical transformations on zirconium surface during machining and electrotechnological treatment with high-frequency currents

Research results on the chemical composition and surface morphological characteristics of zirconium products after machining and treatment with high-frequency currents are described. It was established that at the temperature range from 600 to 1200 °C and duration of heat treatment from 30 to 300 seconds oxide coatings consisting of nano-grains are formed.

Oxide-bioceramic coatings obtained on titanium items by the induction heat treatment and modified with hydroxyapatite nanoparticles

Prospective composite bioceramic titania coatings were obtained on intraosseous implants fabricated from cp-titanium and medical titanium alloy VT16 (Ti-2.5Al-5Mo-5V). Consistency changes of morphological characteristics, mechanical properties and biocompatibility of experimental titanium implant coatings obtained by oxidation during induction heat treatment are defined. Technological recommendations for obtaining bioceramic coatings with extremely high strength on titanium items surface are given.

Microtexturing and nanostructuring of the surface of titanium and its alloy using spark alloying with tantalum and subsequent oxidation

The study focuses on high-performance combined spark alloying of titanium alloy (VT1-0, VT16) surface and porous matrix structure oxidation. The coatings morphology is the result of melt drip transfer, heat treatment and oxidation. The study establishes the influence of technological regimes of alloying and oxidation on morphological heterogeneity.