A. Yu. Ivannikov

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.

Experimental Study of Rewetting of a Superheated Plate with Structured Capillary-Porous Coating by Flowing Liquid Film

The experimental results on rewetting of the surface of a superheated vertical copper heater and a heater with a structured capillary-porous coating (applied by means of directed plasma spraying) by liquid nitrogen film are presented. It is shown that presence of the capillary-porous coating fundamentally influences the temperature variation and reduces the duration of overall plate cooling by more than three times. The high-speed videofilming of the transient processes was carried out and data on the character and structure of the rewetting front were obtained. Analysis of the synchronized measurements of the plate temperature and the high-speed video of transient processes shows that the higher cooling rate in the presence of structured capillary-porous coating is related to the development of intensive boiling in the rewetting front at sufficiently higher plate temperature.

Ultradisperse and nano structures in plasma coatings hardened by electromechanical treatment

For the example of PRFBKh6-2 alloy and P6M5 steel powders, the structure of plasma coatings after electromechanical treatment is investigated by scanning probe microscopy. After such treatment, ultradisperse and nano hardening phases are formed in the coating. These phases are formed by the decomposition of the coating’s initial fast-quenched structure in high-speed treatment. The formation of characteristic structural zones hardened by nanoparticles and ultradisperse particles is analyzed; the proportions of nanoparticles and ultradisperse particles are determined by the parameters of the sprayed powder and the conditions of plasma spraying and subsequent electromechanical treatment.

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.

Composite Coatings Based on Low-Temperature Calcium Phosphates for Intraosseous Implants

A method for obtaining apatite crystallization precursors via chemical transformation of plasma coatings based on α-tricalcium phosphate (α-TCP) into dicalcium phosphate dihydrate (DCPDH) with subsequent hydrolysis into octacalcium phosphate (OCP) is studied. X-ray diffraction (XRD) phase analysis, IR spectroscopy, and scanning electron microscopy (SEM) techniques are used for studying the phase composition and microstructure of the experimentally obtained samples depending on the process conditions. The approach described in this paper makes it possible to obtain two-phase calcium phosphates with different ratios between DCPDH-OCP and hydroxyapatite (HA).

The boundary between the hydroxyapatite coating and titanium substrate

The effect of the heating of a Ti substrate to 300 and 550°C on the microhardness of a hydroxyapatite (HA) plasma coating, Ti, and their interface is investigated in specimens in different states (as sprayed, after hydrothermal (650°C, 3 h) and vacuum heat treatment (800, 1000, 1100°C, 3 h)). It is shown that the preliminary heating of the substrate to 550°C leads to the interface microhardness increasing from 2.32 to 3.07 GPa, while the following heat treatment has a weak influence on that. After the heat treatment, the microhardness of the HA coating is increased from 3.0 to 3.8 GPa and the microhardness of the Ti substrate near the boundary is increased from 2.5 to 6.9 GPa. A slight effect of the heat treatment on the interface microhardness is explained by preservation of the interface structure formed under HA plasma spraying on the heated substrate. The distribution of chemical elements near the interface between the coating and substrate is studied by Auger electron spectroscopy (AES).