Method of forming a wear-resistant coatings

 

(57) Abstract:

The invention relates to the formation of wear-resistant coatings on the aluminum parts of complex shape and large area and can be used in mechanical engineering. The method includes forming process of the insulating layer of inorganic compounds based on immersion in the electrolyte and microarc oxidation. Effect: increase the wear resistance of surfaces in friction, ensuring electric insulation surface, creating thermal barriers in nestacionarnog working nodes, providing corrosion protection.

Innovation refers to the electrochemical machining of metals, mainly valve, for forming on their surface insulating, corrosion-, heat - and wear-resistant coatings in the mode of electrical discharges, and can be used in various fields of engineering:

- to improve the wear resistance of surfaces in friction units;

- to ensure the electrical insulation of the surfaces;

- to create thermal barriers in nestacionarnog working nodes;

- to provide corrosion protection.

Known methods mi is i.i.d. shock with voltage up to 700 V or more, for different ratios of the cathodic and anodic current densities and the total anode-cathode current density of more than 5 A/DM2[1, 2, 3, 4, 5, 6, 7, 8].

These methods receive oxide coating, consisting of two major, substantially different mechanical properties of the layers - upper porous, so-called process, which is typically mechanically removed, and the highly rigid internal dense, carrying the main function.

The formation of the solid layer is preceded and caused the formation of "technological" layer, formed on accederemos metal surface mainly due to electrophoretic and thermal deposition of bath components (hydroxides, silicates, and others).

However, the specificity of the process is such that when the oxidation complex from the point of view of potential distribution (and hence current) surfaces, which include planes, cavities, and even long cylinders, due to the lack of equipotential bits forming the coating (as a porous, electrophoretic inflicted on his part, and the solid resulting from the oxidation bases), focus primarily on the protruding surface is the surface coating is formed from very rarely distributed random germinal zones, gradually growing together provided sufficient investment of energy, because energy installations. Given the limited capabilities of the source relative to the size of the coated surface, the process of accretion of the germinal zones stretched over time and generally may not be terminated. The thickness of the hard coating layer can vary from 100 microns to complete his / her absence up to a local protravel uncovered plots. Such a phenomenon at low current densities can occur on flat surfaces, spaced from the periphery of 10-15 mm, and especially in the hollows.

At the same time, due to the fact that first spark and microarc processes it is necessary to provide the starting current density of 1.5 to 2.0 times the working, when exceeding the size of the coated surface energy capacity installed spark or arc process does not occur, the process of dissolution of the Foundation, and the desired coating is not formed. Most revealing in this respect the process of microarc oxidation in alkaline electrolytes that do not contain silicates or other glioblastoma components necessary for the formation of the primary, "Techna part of energy is spent on creating a process layer due to the products of dissolution and oxidation of the underlying metal.

The known method (device) microarc oxidation, which consists in scanning accederemos surface, due to the gradual immersion of the object into the electrolyte with a parallel change in the electrical parameters mode [9].

This method in its aims are similar to the proposed invention, however, it requires additional rather complicated apparatus and equipment with a precisely calculated nonlinear synchronization of electrical parameters and mechanical movements. At the same time, in this method, oxidation of the surface initiated her spark discharge has contact with the air, which creates a constant noise from small explosions detonating gas bubbles released during the oxidation. All this can complicate the use of this invention on an industrial scale.

Known methods of alignment of current density on the surface of the workpiece used in electrochemical technology, in particular in galvanothermy, to provide conditions for obtaining a uniform coating layer on the surfaces of complex shape, consisting in the use of shaped electrodes [10] or insulating diaphragms - ekrana CLASS="ptx2">

The method using insulating diaphragms screens can be viewed as analogous to achieve uniform distribution of currents on the surface of the oxidation, but it does not give any advantage to reduce the magnitude of the starting current.

The disadvantages of these methods are, first, the necessity of experimental selection of the geometry of the additional devices, secondly, additional place and means of their mounting in the electrolytic third, unavoidable significant costs in the form of korrozionnostojkih materials for the manufacturing of devices.

Closest to the invention is a method of applying an electrolytic coating on the surface of metals and alloys (and electrolytic coating), which consists in immersing the processed material, which serves as the first electrode and the second electrode in the electrolyte, a voltage is applied between them in the form of a slave base load pulses to the ignition of a multitude of micro-discharges, evenly distributed over the surface of the processed material, and maintaining the voltage to obtain a coating of a given thickness, and in addition to the basic impulses on the LOI which have high hardness and density, and the surface of the porous layer qualifies as a technological and, if necessary, can be easily removed by machining for (up to) outcrop of the main solid layer.

Imposed triggering voltage pulses are intended to reduce the starting currents required for the excitation of micro-discharges at source (net, not yet closed technological layer) of the metal surface. However, the proposed reception is not possible to provide a uniform distribution of bits (by their number and cathode-anode ratio) in time over the entire treated surface outside of the shape and size of the presented samples, and therefore, to form a homogeneous process layer and eventually the coating as a whole.

The objective of the proposed method is obtaining a uniform thickness and quality wear-resistant insulating coating on all accederemos the surfaces of large area and complex forms of aluminum and other alloys with the barrier properties. The technical result is:

- uniformity (qualitative and quantitative) coating on all external surfaces and complex shapes;

- Nezavisimoe asked the same density and the anode-cathode ratios current from the size and shape of the parts;

- expanding the technological capabilities of the installation (the possibility of forming a wear resistant coating on the premises, in excess of 2 times the nominal, and minimum concentrations of glioblastoma electrolyte components);

- energy saving due to lower investment of energy in the formation of the outer porous layer and technological reduce starting currents.

The invention consists in that in the method of forming a wear resistant coating comprising immersing the base in an electrolyte and forming on the base layer with the participation of inorganic compounds microarc oxidation, before diving bases in the electrolyte on the surface of the forming process of the insulating layer of inorganic compounds.

The essence of the method lies in the fact that oxidarea surface by a method other than electrolytic, such as thermal spraying or slurry (by spraying, dipping or brush), apply technological coating of the inorganic insulating compounds with uniform end-to-end porosity. This technological coating electrically blocks a significant part of accederemos poverhnosti, like electrolytic membrane, the flow to the reaction (accederemos) metal surface a certain ratio of positive and negative ions. The result is provided to initiate the emergence and further accretion evenly distributed germs oxide coating over the entire surface using a very small current densities as in the initial (starting) stage and throughout the process with the fullest use of energy installations. Thus it is possible to reduce the peak current at the start of the process and further reduce the energy costs of the formation of the upper porous layer, which is the main process of formation of the solid layer. This allows formation of microarc oxidation is of uniform quality and thickness of the coating on the surfaces of awkward shaped area 2-3 times greater than the installation (source). When this pre-applied technology layer at the end part of the upper porous layer formed by electrolytic coating.

The coating was subjected to flat samples (objects) of the alloy D16 and AMG.6 size HH mm (two-sided p is and D16 previously subjected to etching in alkali for removal of the cladding layer.

Oxidarea the surface of the base was subjected abrasive-blasting grain abrasive 40-100 μm and then degreased by wiping with a tissue swab moistened with benzine.

On oxidarea prepared in this way the surface of the base layer applied technology coating thickness of 0.05-0.03 mm by methods of thermal (plasma) spraying of powders of inorganic compounds and atomization of the slurry.

Method of thermal spray applied layer or aluminum oxide (Al2ABOUT3), or aluminum oxide with additives of titanium oxide (up to 13 wt.%), or magnesia spinel (MgOAl2O3). Open (through) the porosity of the applied coatings were 10-20%.

The method of pulverizing the applied layer of the slurry on the basis of potassium or sodium liquid glass with oxide additives M5, or titanium oxide, or their mixtures, or magnesia spinel with grain size less than 10 μm at a ratio of liquid and solid phase of the slurry by weight of 1:1 when diluted suspensions with distilled water in the ratio (2 mass fraction of slip): (1.0 to 1.5 fraction of water). Thus formed coating was dried in a drying Cabinet at 50oC for 0.5 hours left 15-25%.

Technological coating was applied to the entire oxidarea the surface of the base or on the part of the surface, the most unfavorable from the viewpoint of oxidation conditions (potentially less loaded), namely for the processing of objects in the zone, located at a distance of 10-20 mm from the edge. On the control objects of technological coating was not applied.

The thus prepared base was immersed in the electrolytic bath using tokovodov, isolated from contact with the electrolyte and subjected to the microarc oxidation.

Oxidation was performed in an electrolyte consisting of an aqueous solution of sodium hydroxide (2.0 g/l) and liquid sodium glass (6 g/l) with an average total anode-cathode current density of the process 7 A/DM2when the ratio of the density of the cathodic and anodic currents from 0.9 to 1.1. The initial (starting) current density does not exceed a finite current density of more than 10%.

The exposure process was 6 hours, which corresponded to the total passage of electricity 40 Ah/DM2.

On the part of control objects size of 100x100 mm without technological coverage average total anode-cathode current process established 20-30 And/CLASS="ptx2">

Objects after oxidation were subjected to metallographic analysis with measurement of layer thickness and microhardness.

The results of the experiments.

1. The objects of the alloy D16 with all technology used by coating to a thickness of 200 μm thickness of the base layer having a hardness in the range 1300-1800 kg/mm2on the entire surface averaged 80 μm when the thickness difference between edge and middle zones of no more than 10%.

2. The objects of the alloy.6 with all the technology used by coating to a thickness of 200 μm thickness of the primary oxide layer having a hardness in the range 1000-1400 kg/mm2on the entire surface averaged 100 μm when the thickness difference between edge and middle zones of no more than 10%.

3. At sites with technology coating thickness of 250 μm or more as a result of oxidization under technological coating was obtained highly porous (>20%) of the oxide layer of low hardness thickness of 150 microns.

4. At the control sites, oxidized at current density of 7 A/DM2in the middle zone, located at a distance of 20 mm from the edge, formed mordant agent (ulcers protravel) in the absence of this area firmly Lina solid layer had a zonal in nature and differed between the regional and Central areas 2-3 times (80 μm - at the edges, 30 μm or less in the area of 40 mm from the edge), and in the center was the adhesion of the coating, until the complete absence of the dense layer.

Literature

1. Copyright certificate 1200591, CL 25 D 11/02.

2. RF patent 2019582, CL 25 D 11/00, 11/02.

3. RF patent 2026890, CL 25 D 11/02.

4. RF patent 2077612, CL 25 D 11/02.

5. RF patent 2081212, CL 25 D 11/02.

6. RF patent 2082838, CL 25 D 11/02.

7. RF patent 2110623, CL 25 D 11/02.

8. RF patent 2119558, CL 25 D 11/02.

9. RF patent 2010040, CL 25 D 11/02.

10. Century. And. Liner and N. T. Kudryavtsev. Fundamentals of galvanothermy, part 1. Metallurgizdat, 1953. Moscow. S. 254, 255.

11. A. M. Yampolsky and C. A. Ilyin. Quick reference electroplating. The motor cycle", 1962. Moscow, Leningrad. S. 151-153.

12. RF patent 2112086 C1 IPC 6 25 D 11/00.

Method of forming a wear resistant coating comprising immersing the base in an electrolyte and forming on the base layer with the participation of inorganic compounds microarc oxidation, characterized in that before diving bases in the electrolyte on the surface of the forming process of the insulating layer of inorganic compounds.

 

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