Investigation of the electrospark coating, alloying and strengthening technology

Introduction. The work objectives were the analysis and application of the technology of electrospark deposition of wear-resistant metal coatings on cutting tools or machine parts for their hardening or dimensional restoration.Materials and Methods. The technology, device and principle of operation of the modernized installation intended for electric spark application of wear-resistant metal coatings with composites T15K6, VK8 and VK6 are considered.Results. To determine the parameters of the upgraded electrospark alloying plant, experiments were carried out on hardening of polished samples made of steel 45 with hard alloy T15K6 with dimensions of 25×25×25 mm. As a result of using the experiment planning method, the possibility of selecting and adjusting the installation parameters was confirmed. The following parameters were selected for hardening samples made of steel 45 with hard alloy T15K6: current I = 1-2–A, voltage U = 40-75 V, capacitor bank capacity = 60–100 µF.Discussion and Conclusions. The use of carbon dioxide as a protective medium enables to increase the number of passes and, accordingly, the number of coating layers to twenty, to obtain a total thickness of up to 0.3 mm with a dense structure without oxides. Coatings of this thickness make it possible not only to strengthen, but also to restore the dimensions of worn machine parts. The parameters of the technological modes of electrospark alloying significantly affect the intensity of coating application and the quality of the resulting surface. A rise in the electrical parameters causes an increase in the intensity of each individual discharge and, within certain limits, contributes to an increase in the amount of the transferred coating material, as well as to deeper transformations of the coated surface in the discharge zone. Thus, an electrospark alloying plant equipped with monitoring and diagnostic tools, as well as with a protective gas supply system, can be used for hardening and restoring machine parts and cutting tools.

DEVELOPMENT OF DEVICE FOR RESTORATION OF PLACES FOR BEARINGS

Defects of case details include operation of openings under bearings within 0,2 - 0,4 mm on the party, operation of landing belts under sleeves. When restoring them, traditional methods are used: installation of repair bushings, application of polymer and electrolytic coatings, micron smelting, electrospark treatment, etc. Restored parts must have hardness and wear resistance with the parameters of the material of the reducing part (deviation 10 - 15%), have sufficient adhesion to the base metal, corrosion resistance in a humid environment, provide maximum contact area with the conjugate part, no pores, slag, foreign inclusions . The method of restoration must eliminate the thermal impact on the part and be cost-effective. Polymer compositions are usually brittle, subject to breakage and leaching. Surfacing causes warping of the part, bleaching of cast iron, the formation of slag and pores in the deposited layer. The electrospark coating method does not provide sufficient contact area with the conjugate part. The use of electrolytes for iron seats in some enterprises is aggressive, unstable, requires heating or the use of expensive thyristor power supplies, followed by machining, as the microhardness of precipitation reaches a large value depending on the composition of the electrolyte and process modes, have high internal voltage. The proposed device for restoring the bearings simplifies the existing method and meets the technical requirements of manufacturers in terms of machining accuracy (ovality, taper, coaxiality and surface roughness), provides high productivity (2 times higher than the productivity of specialized machines horizontally). and low cost (60 times lower than the cost of specialized machines).

RESEARCH OF EROSION RESISTANCE OF SOLDERED JOINTS WITH PROTECTIVE COATINGS

Presents results of studies of the erosion resistance of soldered joints with various types of coatings. It was established that a coating based on tungsten carbide, applied by the electrospark method, has the greatest positive influence on the erosion resistance of VPr4 solder. At the same time, preliminary machining of the solder surface also increases resistance to the effects of erosion flow. The possibility of using an electrospark coating as an erosion-resistant sublayer for composite protective coatings was shown.

Microgeometrical characteristics of electrospark coatings in the initial state

Microgeometric parameters of the effect of discrete electrospark coatings on their stress-strain state have been evaluated for the case of using a combined technology of modification of duralumin D16, which includes the technique of electrospark alloying with subsequent surface plastic deformation of coatings formed. According to the profilograms of discrete electrical coatings, the curves of the bearing surface (Abbott curves) were constructed and the parameters that drastically affect tribological characteristics of the coatings were determined. It was shown that modification of duralumin D16 with a combined electrospark coating VK-8 + Cu reduces the arithmetic mean height of peaks in the top portion of the profile by 4.4 and 3.2 times, doubles the arithmetic mean depth of the profile core irregularities, increases the arithmetic mean depth of profile valleys by 1.8 and 1.1 times, in comparison with electrospark coatings from hard alloy VK-8 and copper, respectively. These parameters help to reduce the period of running-in of the contact surfaces strengthened by the combined electrospark coating VK-8 + Cu, increase their bearing capacity, contact durability and specific oil consumption. On the basis of the finite element analysis method of the Nastran software complex, a model of the stress-strain state of a discrete coating/base was designed and distribution of the main normal stresses was determined for a coating compactness of 60% under a normal load of 600 N. The performed modeling revealed advantages of a combined technology for formation of wear-resistant electrospark coatings, which consists in turning residual tensile stresses into compressive ones. When modifying the duralumin D16 with a VK-8 + Cu coating, on the coating surface and in the base material, compressive stresses (-93 MPa and -20 MPa, respectively) are formed, which provides a decrease in wear of the modified surface by two times compared to unmodified duralumin D16.

ELECTROSPARK COATING PROCESSING WITH METHOD OF ULTRASONIC PLASTIC DEFORMATION

In the paper there are shown results on roughness parameter decrease on the electrospark coatings of 20H13 and 30 steel surfaces by means of smoothing with the use of the plant for non-abrasive ultrasonic finishing (NUF). For the coating formation there were used Ni, Cu and an intermetallic alloy based on Ni3Al phase. At the NUF increase of coatings formed with the use of Cu there is a roughness growth caused with material “pickup” upon an indenter. It is determined that for smoothing the surfaces with electrospark coating with the assurance of roughness considerable decrease a six-fold NUF processing is required. A microstructure of the coating obtained with the use of anode material based on the Ni3Al alloy consists of columnar crystal grains the cross-section dimensions of which change from some mkm to several tens of nm. Crystal grains are directed mainly normally regarding a cathode surface. By means of micro-X-ray spectrum analysis there is defined an elementary composition of columnar crystal grains corresponding to the alloy of the Nix-Aly-Fez system which is alloyed with Cr and contains admixtures of Si and Mn. By means of the microstructure investigation of the coating smoothed surface in a number of areas there are revealed crystal grains with the signs of plastic deformation.

The Study of the Electrospark Coating Effect on the Heat Removal Property of Hard Alloy

The effect of a protective coating on the heat removal properties of a cutting plate made of VK8 tungsten-containing hard alloy has been studied. The article provides a sequence of measurements made by a thermal imager and a thermograph to install a mechanism for heat removal by a protective coating. The factors affecting the fault in temperature measurements in a static experiment by means of a thermal imager are described. The time to maximum temperature transferred from the heated counterbody to the hard alloy with and without coating has been obtained. The exposure time of the maximum temperature transmitted from the counterbody to the alloys under study has been fixed. It has been demonstrated that a multilayer electrospark coating based on Ni, Cu, Fe, Cr, W reduces the maximum temperature under the same test conditions by 42%, while the surface cooling rate at the point close to the cutting edge increases by 53%. The data obtained show the effect of the protective coating on the heat removal property of the hard alloy. The time of heat propagation over the entire surface of the test sample and the cooling time have been studied by means of a thermograph. There is a temperature difference of 103°С for the alloy without coating that has been calculated simultaneously between the points on the cutting edge and at a distance of 2 mm lower along the front surface, while for the alloy with a protective coating the difference was 79°С, it is less by 24%. The thermograms of alloys with and without coating are clearly shown at time to maximum temperature on the surface. The work of the coating to remove heat from the point of contact with the heated counterbody has been proven, and the heat removal property is explained by the composition of the coating obtained by electrospark alloying with electrodes based on Cu, Ni, Fe, W, and Cr

Influence of structural graphite surface electrospark machining conditions on erosion resistance

The study deals with the erosion resistance of graphite samples with an electrospark coating surfaced in different conditions. The purpose of the study was to identify the coating of better quality. During the experiment, three metals were used as the anode: tungsten, titanium, and vanadium. For erosivity, plasmatron was used

Evaluation of Wear Resistance of Copper at Sliding against TiC Based Coatings under Load

An evaluation of the adhesion interaction of copper and TiC-based coatings formed by electrospark deposition using TiC based electrodes (SHIM mark) was carried out. Tribological tests of the samples were carried out using Pin-on-Disk testing machine. It is established that the least (0.07) coefficient of friction has a electrospark coating deposited of electrode material contained tungsten additives. After tests on the optical profilometer, it was found out that some coatings do not have adherence of the wear products of the copper counterbody. So, it was found two different types of interaction of the copper counterbody with the coatings - with adherence and without adherence (so called wear less sliding behavior) which is perspective to develop novel deforming tools.

Study of erosion resistance of graphite MPG-7

The study focuses on the erosion resistance of graphite samples with an electrospark coating. To compare the experimental results, we chose titanium, tantalum, tungsten, stellite as a hardening coating. For erosion, we used an installation to obtain high-enthalpy gas flows, the installation combining a plasma gun and an aerodynamic device, by means of the latter a gas flow is formed.