Yu. S. Borisov

Reactions in the Cr-SiC system under conditions of ordinary and plasma heating

Progress in new fields of technology is inseparably linked with the formulation of materials possessing specialmechanical and physicochemical properties as well as with the use of protective coatings for improving the quality of parts. A promising direction in research on coatings with special properties is the production of multiphase coatings consisting of mixtures of carbides and silicides of transition metals, in particular chromium. One way of producing mixed carbide-silicide coatings or materials is to utilize the reaction of chromium with silicon carbide.

Structure and properties of gas-thermal coatings of Fe-B-C and Fe-Ti-B-C alloys

This article presents the results of investigations of the structure and certain properties of gas-thermal coatings of Fe/sub 61/B/sub 37/C/sub 2/ and an alloy of similar composition with the addition of titanium which may be described by the formula Fe/sub 67/Ti/sub 7/B/sub 24/C/sub 2/.

Reaction of boron carbide with titanium under ordinary and plasma heating conditions

ConclusionsAs a result of an investigation, into the high-temperature solid-phase reaction of boron carbide with titanium under ordinary and plasma heating conditions, it has been established that the reaction, which begins at 1300°C, is slow in its final stage, which is due to the appearance of a zone of porosity and to disturbed contact between the reactants. Because of this, in spite of its being accompanied by an appreciable thermal effect, the reaction fails to proceed to completion under conditions of both continual ordinary heating (to 1600°C) and plasma heating. It is possible to obtain spray-deposited coatings of the required composition (TiC+TiB2) by employing preconglomerated or clad Ti -B4C powders and preheated basis plates.

Structure and properties of chromium-carbide composite materials and coatings

ConclusionsEutectic chromium-carbide composites show promise as materials for coatings applied by the plasma spray-deposition technique. Use of composite powdered mixtures of chromium and carbides enables coatings to be obtained having phase compositions identical with those of cast alloys. The plasma spray-deposited Cr-TiC, Cr-TaC, and Cr-NbC coatings investigated were found to be superior in wear resistance to sintered alloys of the same compositions and to both cast and plasma spray-deposited chromium. The chromium-carbide composite coatings retained their good wear resistance up to 1000°C. The best results were obtained with Cr-11% TiC and Cr-27% TaC materials. Coatings of this type would appear to be particularly suitable for service under conditions of high-temperature wear in an oxidizing atmosphere, such as are encountered in metallurgical and power generating installations and gas turbine engines.

Investigation of the thermal cyclic life of coatings for combustion chambers of gas turbines

We present the methods and results of an experimental investigation of the thermal cyclic life of five types of plasma heat-resistant thermal-barrier coatings on the combustion chamber of a gas turbine in a high-temperature gas flow. We analyze the thermal stressed and strained state of an element of the fire tube for three types of coatings by performing several variants of numerical calculations and study the influence of coatings on the thermal stresed and strained state of the composite and the character of its damage.

Contemporary achievements in the deposition of protective and hard coatings

Information is presented on the status of development of methods of gasothermal and vacuum deposition of coatings. Coating deposition for the protection of surfaces against wear and corrosion, or to provide specific useful properties (thermophysical, optical, electromagnetic) is one of the important trends in the development of new materials for machinery construction. The selection of different materials for the base and coating in order to combine mechanical strength with resistance to aggressive environments enables construction of more reliable components while conserving materials. A series of commercial methods based on gasothermic and vacuum technology permit the achievement of high output through the use of automation. Prospects for further development of these methods lie in devising combinations of techniques, the use of supersonic jets, high energy beams and impulses, and supplemental treatment of coated parts.

Effect of coating porosity on the process of heat transfer with gas-thermal deposition

Features are considered for the thermal state of layered-inhomogeneous systems of a multilayer coating—underlayer—base with plasma deposition of cladding composite powders. Typical results are presented for mathematical modeling of the quasistationary process of heat transfer for the system in question. Regularities of the effect of coating porosity on the temperature schedule for the system and the effect of coating thickness on porosity are studied.

Structural characteristics of flame-sprayed Fe-Ni-B alloy coatings

ConclusionsFlame-sprayed Fe40Ni40B20 alloy coatings have a mainly amorphous structure with a small amount of fine, 0.5- to 1-μm.crystalline inclusions. The crystalline phases are (Fe, Ni)3B and Fex Ni23-xB6. The structure of the precipitated crystalline inclusions in the amorphous matrix is not related to that of the eutectic of the starting alloy powder used for spraying. In the direction from the base to the free surface the coating structure varies: The volume concentration of the crystalline phases changes, which is reflected in the emission of secondary ions of the main components of the deposited alloy.

Production and structure of flame-sprayed coatings based on Ni-Ci-B-Si alloys

Hydroabrasive wear tests on coatings were conducted in a 333-US apparatus at the Mekhanobr Institute. The test specimens were 35-mm-diameter cylindrical bshings of 20Kh13 (0.2% C13% Cr) steel, to the side surfaces of which coatings were applied. The abrasive was En-1.25 electrocorundum. The test results obtained showed that the wear resistance of heattreated coatings of a self-fluxing alloy with a binary titaniumchromium boride addition and of untreated coatings from the VSNGN-35+ SNGN-55 + Ni-Al mechanical mixture was 1.5-2 times higher than that of 20Kh13 steel and 3-4 times higher than that of a spray-deposited coating of PG-SR4 self-fluxing alloy. The application of protective A1Y alloy layers has enabled the heat treatment of coatings of self-fluxing alloys to be performed in ordinary furnaces in air, without any detectable oxidation of the main layers.

Antifriction properties of thermal sprayed coatings from clad carbide powders

In the present work a study was made of the antifriction properties of sprayed coatings on VT-22 titanium alloy. Specimens were sprayed with titanium and chromium carbides clad with cobalt, copper, or nickel. Cladding was performed by an autoclave method consisting in reducing copper, cobalt, and nickel from salt solutions with hydrogen under pressure. The thickness of the cladding layers was 3-5 ~m, which was equivalent to 35-40 wt. %. For purposes of comparison, tests were carried out also on specimens of the titanium alloy provided with chromium electrodeposits and with oxide coatings (Table 1).