M. M. Student

Optimization of the Chromium Content of Powder Wires of the Fe–Cr–C and Fe–Cr–B Systems According to the Corrosion Resistance of Electric-Arc Coatings

We study electric-arc coatings of the Fe–Cr–C and Fe–Cr–B systems. It is shown that chromium content of 12 wt.% is insufficient to guarantee higher corrosion resistance of the coatings in neutral aqueous solutions (as compared with steels) caused by the formation of chromium-based oxides, carbides, and borides. Therefore, the indicated chromium content of the compounds should be taken into account and compensated in finding the chemical composition of powder wires. Its unjustified increase is not reasonable because powder wires are characterized by filling coefficients restricting the possibility of their filling with alloying elements. Therefore, the content of each alloying element in the charge of powder wires should be well justified and determined. For this purpose, we propose to use the relations taking into account the nonlinear distribution of chromium in the lamellas of the coatings caused by their high microheterogeneity and the depletion of their solid solution of the indicated element as a result of the formation of oxides, carbides, and borides on its base.

Corrosion Resistance of Plasma-Electrolytic Layers on Alloys and Coatings of the Al–Cu–Mg System for Various Modes of Heat Treatment

We study the influence of its microstructure of an Al–Cu–Mg alloy sprayed by the electric-arc method in the intact state and with oxide-ceramic coating on its corrosion resistance in synthetic weakly acid media. It is shown that the increase in the temperature of annealing the electric-arc coating results in the growth of Al2Cu intermetallic inclusions acting as cathodic inclusions and increasing the sizes of pores in the oxide-ceramic coatings. These changes promote a significant increase in corrosion currents both in the electric-arc coating and in the oxide-ceramic layer on it. It is shown that the corrosion currents formed in the electric-arc coatings without oxide-ceramic layer are stronger by an order of magnitude.

Improvement of the Anticorrosion Properties of a Working Emulsion of Mine Hydraulic Systems

We seek new efficient corrosion inhibitors for the protection of steel rods of mine hydraulic cylinders with electric-arc sprayed coatings against corrosion in the FMI-RZh working emulsion contaminated with chloride ions. A significant deceleration of the corrosion fracture of 45 steel is detected after the addition of sodium silicate and benzyl benzoate to the emulsion. The inhibiting effect of benzyl benzoate can be explained by the adsorption of its polar molecules on the steel surface and by the formation of sodium benzoate as a result of the reaction with hydroxyl ions near the cathodic sections. Both inhibitors provide the efficient corrosion protection of the “45 carbon steel–electric-arc sprayed powder-wire coating” system in a 3% solution of sodium chloride under the conditions of leakage of the inhibited emulsion through the porous sprayed layer.

Corrosion Resistance of the Metal Vibration Deposited from Flux-Core Wires Based on the FE–CR–B System

We study the corrosion resistance of coatings obtained by submerged-arc built-up welding. The fused metal is obtained from Fe-based flux-core wires of the Kh10R4G2S grade. On the basis of the results of phase analysis, it was discovered that the fused metal is formed by a FeCr matrix and a solid solution of Fe2B and (FeCr)B borides. This observation was confirmed by the data of spectral analysis. It is demonstrated that the application of horizontal vibration with an amplitude of 300 μm in the course of surfacing leads to the dispersion of the Fe2B and (FeCr)B boride phases down to 2–5 μm2, which increases the resistance of fused metal to abrasive wear. The mass losses in the cases of wear with fixed and nonfixed abrasives are made 2–2.5 times lower. It is also shown that the procedure of surfacing performed in the presence of vibration negatively affects the corrosion resistance of the welded metal obtained from Kh10R4G2S flux-core wires due to the increase in the fracture of cathodic inclusions.

Microstructure and Abrasive-Wear Resistance of the Vibration-Deposited Metal of Core Wires of the Basic Fe–Cr–B System

We investigate the microstructures of fused layers obtained by the welding from a core wire made of Kh10R4G2S steel. The presence of Fe2B and (FeCr)B inclusions distributed against the background of the matrix (solid solution of FeCr) in the microstructure of fused layers is confirmed by the phase and spectral analyses. If no vibration is used in the process of welding, then the sizes of borides vary from 10 to 150 μm2 (in the central part of the rollers) and from 50 to 300 μm2 (in the zone of overlapping of the deposited layers). The maximum effect of grinding of the (FeCr)B and Fe2B phases (up to 2–5 μm2 at the centers of the rollers and in the zone of their overlapping) was obtained by applying horizontal vibrations with an amplitude of ~ 300 μm in the course of welding. As a result, the microhardness of the fused layers increases and their abrasive wear resistance is also improved. The weight losses observed in the tests with fixed and nonfixed abrasives become 2–2.5 times lower.

Electrochemical Properties of the PEO Coatings on AZ31 Magnesium Alloy Produced by Different Technologies

We study the structure and electrochemical properties of AZ31 alloy obtained by the classical procedure of duo rolling as well as by the methods of extrusion and thixoforming in the intact state and with oxideceramic coatings synthesized in plasma electrolytes. It is shown that, for different technologies of the production of the alloy, the Mg17(Al, Zn)12 intermetallic inclusions formed in this alloy have different sizes and shapes. The largest inclusions pass into the plasma-electrolyte oxide-ceramic coating and play the role of cathodes in corrosion processes. The alloy produced by the method of thixoforming has the highest electrochemical properties both in the intact state and with oxide-ceramic coatings. Independently of the method of production, the plasma-electrolyte oxide coatings improve the corrosion resistance of the alloy by 2–3 orders of magnitude.

Influence of Vibration in the Course of Surfacing of a Protective Layer on Its Microstructure and Impact-Abrasive Wear

We study the microstructure of a Kh10R4G2S flux-cored wire surfaced under the conditions of vertical vibration with different amplitudes. The microstructure of welding beads is formed by the solid phases of FeCrB carboborides and the matrix in the form of a solid solution of FeCr. It is shown that the vibration promotes the grinding of solid phases and the homogenization of the solid solution. In the surfaced layers formed for an amplitude of vibration of 0.3 mm, the microhardness is uniformly distributed on a level of 900 HV. It is established that the impact wear resistance of these layers becomes 2–2.3 times higher.

Effect of Friction on the Structural and Phase Transformations in the Subsurface Layer of a FeCr + Al + C Gas-Thermal Coating

Under the conditions of frictional interaction, the structural and phase composition of the material of subsurface layers in the intact state and its changes in the course of friction are important factors largely determining the characteristics of wear resistance. In [1], we studied some specific features of the formation of some promising reconditioning coatings applied by the method of electric-arc metallization from powder wires of the FeCr + Al + C system as well as their cohesive, adhesive, and tribological characteristics. It was shown that these coatings are quite efficient both for the reconditioning of worn machine parts and for the enhancement of their wear resistance. In the present work, we study the influence of frictional interaction on the structural and phase state of the subsurface zone of the coatings and the parameters of the processes of friction and wear.