A. A. Radyuk

The shear strength of three-dimensional capillary-porous titanium coatings for intraosseous implants

A plasma spraying process for the deposition of three-dimensional capillary-porous titanium coatings using a wire has been developed. In this process, two additional dc arcs are discharged between plasmatron and both the wire and the substrate, resulting in additional activation of the substrate and the particles, particularly by increasing their temperature. The shear strength of the titanium coating with 46% porosity is 120.6 MPa. A new procedure for estimating the shear strength of porous coatings has been developed.

The influence of three-dimensional capillary-porous coatings on heat transfer at liquid boiling

The process of heat transfer at pool boiling of liquid (Freon R21) on tubes with three-dimensional plasma-deposited capillary-porous coatings of various thicknesses has been experimentally studied. Comparative analysis of experimental data showed that the heat transfer coefficient for a heater tube with a 500-μm-thick porous coating is more than twice as large as that in liquid boiling on an otherwise similar uncoated tube. At the same time, no intensification of heat exchange in the regime of bubble boiling is observed on a tube with a 100-μm-thick porous coating.

The Effect of Resistance Spot Welding on Plasma Sprayed Coatings

The processes of thermoplastic treatment of plasma sprayed coatings made of 10R6M5 high speed steel, Kh20N80 nichrome, FBKh6-2 cast iron, and WC-Co and TiC-NiMo cermets upon resistance spot welding are investigated. Consolidation and deformation (up to 56% in the center of the spot weld) of the coating materials, reduction of the number of structure defects within the boundaries between the sprayed particles, and an increase in the cohesive strength and microhardness of coatings (up to 2.5 times for the 10R6M5 high speed steel) are shown to occur upon welding.

Structure and shear strength of implants with plasma coatings

Four types of three-dimensional plasma capillary-porous titanium coatings for model intraosseous implants are developed. By means of pulsed microplasma oxidation in solutions or plasma spraying of powders, additional bioactive coatings on the basis of calcium phosphates are deposited on the Ti coating surface. Shear strength values of the interface between the implants coated and osseous block after 16 weeks of implantation are 4.25–4.81 MPa, while for implants with additional plasma hydroxyapatite coating it exceeds 6.19 MPa after 4 weeks of implantation.

Structure and mechanical properties of three-dimensional capillary-porous titanium coatings on intraosteal implants

We developed a process of plasma wire spraying of three-dimensional capillary porous titanium coatings for intraosteal implants with the use of two additional arc discharges between the plasma gun and the wire and between the plasma gun and the substrate. By raising the temperature of sprayed particles and activating the substrate, we enhanced the shear strength up to 120 MPa for a titanium coating having the porosity of 46%.

Hydroxyapatite-based coatings for intraosteal implants

Using the buy-to-fly ratio for sprayed material, we optimized the method of creating nanostructured plasma coatings based on hydroxyapatite. After plasma spraying, the coating contains 67–83% hydroxyapatite phase. We studied several case of hydrothermal treatment of coatings for the purpose of strengthening them and in order to increase the hydroxyapatite phase content. After hydrothermal treatment of the coating at 650°C, we achieved the value of hydroxyapatite content around 98%. The size of coherentscattering regions grew from 95 to 122 nm. We proved that, after the treatment, the shear strength of hydroxyapatite-based coatings in relation to the titanium substrate is 22.3 MPa.

The shear strength of Ti–HA composite coatings for intraosseous implants

Plasma spraying of composite coatings is developed and investigated. Three-dimensional capillary porous titanium (3DCP Ti) coatings with a thickness of 1 mm are sprayed using a wire. Hydroxyapatite (HA) coatings with a thickness of 0.08–0.35 mm are sprayed on 3DCP Ti coatings at a temperature of 300–550°C. The joint between the coating and plastic is analyzed at shear. The plastic simulates bone tissue that grows into the coating surface. The heating of the 3DCP Ti coating to 550°С when the HA coating is being sprayed increases the shear strength of the coating with respect to the plastic to 9.8 MPa. Modeling approximations are proposed for the shear of the joint between the coating and the plastic.

Plasma coatings of mechanically doped Co-C-Mo and Co-C powders

X-ray structure analysis and metallography are applied for investigations into the phase composition and structure of powdered model alloys Co-9.2% C and Co-1% Mo-9.2% C after various treatments (mechanical doping, thermal treatment, sintering) and plasma coatings produced from these powders. It is demonstrated that carbides CoxCy are formed within mechanical doping and plasma spraying, which are absent in the equilibrium state diagram. High microhardness of plasma coatings (up to 8.3 GPa) is associated with formation of carbides and amorphous phase. Carbon losses at stages of plasma spraying of coatings are determined.

Variation of Contents of Carbon, Nitrogen, and Oxygen upon Formation of Plasma Cermet Coatings with Steel Matrix Reinforced with Titanium Carbide

This article describes comparative studies of a coating made of high-speed steel and cermet powder on its basis with 50 vol % of TiC strengthening carbide phase. Coatings are formed by Ar–N2 plasma with local protection by powders with particle sizes from 25 to 55 μm. It is demonstrated that the TiC content in the coating is retained, but the lattice constant of this phase decreases from 0.43212 nm for powder to 0.43035 nm in the coating because of variation of contents of carbon, oxygen, and nitrogen. After plasma coating of 50 vol % TiC–R6M5 powder, the average carbon content in the coating decreases from 7.83 to 6.74 wt %. The oxygen content in the cermet coating increases to 2.8 wt % in comparison with 0.8 wt % in the initial powder. The nitrogen content also increases from 0.05 to 0.89 wt %. The microhardness of particles of initial powders of high-speed steel is 8.91 GPa, and that of 50 vol % TiC–R6M5 cermet is 9.5 GPa. The microhardness of the cermet coating, 11.0 GPa, corresponds to the calculated value obtained by the mixture rule at microhardness of the R6M5 steel coating equal to 6.64 GPa.

Structure and Wear Resistance of Plasma Coatings Sputtered Using TiC + HSS Binder Composite Powder

The elemental and phase composition, macro- and microstructure, hardness, and abrasive wear resistance of coatings obtained via a plasma sputtering of a high-speed steel (HSS) P6M5 powder and a (TiC + 50 vol % of P6M5) powder obtained using a self-propagating high-temperature synthesis procedure are studied. The structural state of oxygen and nitrogen impurities and their effect on the properties of coatings are considered. It is established that the metal-matrix structure of the composite powder remains unchanged in the sputtered coating, which causes a 2.0-fold and 7.6-fold increase in the hardness and wear resistance of the composite coating, respectively, in comparison with the coating obtained via sputtering of steel powder.