EXPERIMENTAL SELECTION OF ELECTRIC SPARK TREATMENT FOR ELECTRODES OBTAINED BY VARIOUS METHODS

Electric spark surface treatment is widely used in repair production. Its high versatility is ensured by a wide range of electrical modes and the possibility of using all conductive materials as electrodes. The selection of optimal electrical modes of the electric spark processing installation is important for obtaining high-quality coatings when using a specific electrode. This problem is especially acute for new electrode materials obtained from machine-building waste, since such electrodes are still poorly studied. (Research purpose) The research purpose is in experimentally selecting optimal modes of electric spark processing of steel parts for each of the electrodes under consideration for using the obtained data in further research. (Materials and methods) The article presents electrodes made of bronze grade BrAZh9-4 according to GOST 18175-78 and from secondary bronze powder. The coatings were applied using the Vestron AI-007 electric spark treatment unit on steel samples. The analytical scales Acculab ALC-210d4 and the micrometer MG H25 GOST 6507-90 were used. (Results and discussion) All coatings were applied to samples with an equal area in three layers under different processing modes. The increase in the thickness and mass of the electrode material on the sample surface was measured. The article presents formulas and graphs based on the results of the work. (Conclusions) For each electrode, the optimal mode of electric spark processing was chosen, which would further help to compare the electrodes by the quality of the coating formed. The performance characteristics of sintered secondary bronze powder, almost similar to the characteristics of standard materials, prove the feasibility of obtaining such powders by the energy-efficient method described above.

Selection of electric spark processing modes for electrodes from sintered bronze

The method of electrospark machining has proven itself well in the technology of repair and restoration of parts. The operational properties of coatings obtained by this method depend on the microstructure, chemical and phase composition of the electrode materials. A significant improvement in operational properties, for example, wear resistance, is achieved by the formation of nanostructured coatings using electrodes with a certain content of alloying nanomaterials. It is possible to obtain such materials at the lowest cost by electro-erosion dispersion of machine-building waste. This article discusses the electrodes obtained by sintering bronze powder obtained by the method of electroerosive dispersion. Such materials are new for the process of electrospark machining; therefore, it is important to study and select the optimal application modes, since a qualitative characteristic of the process is the indicator of the transfer of the electrode material to the part, which depends on the processing modes and installation parameters. The aim of the study is to select the modes of the installation for electrospark treatment for optimal deposition of the material, as well as to study the degree of coating increment during electrospark treatment. Coating was carried out using an installation for electrospark treatment mod. «Westron» type AI-007, electrode material was obtained by the technology of spark plasma sintering of bronze powder, surfacing was carried out on steel samples 14 × 14 × 40 mm in size, the work also used an Acculab ALC-210d4 analytical balance and an MG micrometer Н25 GOST 6507-90. All coatings were applied to samples with an equal area in three layers under different processing conditions. After that, the increment in the thickness and mass of the electrode material on the sample surface was measured. Based on the results of the work, formulas were obtained and graphs were built. The most optimal mode of coating with an electrode made of sintered bronze obtained from machine-building waste by the method of electroerosive dispersion was determined, which proves the consistency of this method of obtaining electrode materials.

STRENGTHENING THE PORE WALLS OF Al FOAMS WITH SURFACE-ALLOYING TECHNIQUE

This paper describes a new method for surface-alloying treatment to strengthen the pore walls of Al foams using the powder metallurgy method. The advantage of this technique is that the pore walls of Al foams can be enhanced efficiently during the process of preparation. Spherical carbamide particles coated with bronze powder were employed as space-holder. The pore configuration depends mainly on the distribution of space-holder particles during the cold compacted process. The phase components of the modified Al foams were studied by X-ray diffraction Rietveld refinement. Results show that the strengthening effect on the mechanical property of Al foams is significantly related to both phase compositions and phase grain size among the pore walls.

ANALYSIS OF TRIBOLOGICAL PROPERTIES OF SELECTED PTFE-BASED POLYMER COMPOSITES IN A SLIDING INTERACTION WITH ALUMINIUM OXIDE (Al2O3)

The paper presents the microstructure and mechanical and tribological properties of polymer composites based on polytetrafluoroethylene (PTFE) intended for use in friction couples where reciprocating motion is performed, e.g., in compressors or actuators. Micromechanical tests carried out using the Oliver-Pharr method showed that the PTFE composite with a 40% bronze content (T8B) had the most advantageous mechanical properties (hardness H, Young’s modulus E). In turn, tribological tests that were conducted using a ballon- disc tester in the linear (reciprocating) motion showed that the polytetrafluoroethylene composite with a mixture of 25% bronze powder and 15% graphite (T4GM) had the lowest tribological wear. The tribological properties of composite T5W with 25% graphite content were not much worse. Despite the most favourable mechanical parameters, the tribological wear of composites T8B and PTFE with glassy carbon (T3Ws) was nearly twice higher due to the absence of grease formed by a graphite filling. The results show that the use of composites containing a bronze-graphite filling improves the service life of lubricant-free friction couples that perform reciprocating motion.

Properties of Sintered Bronze-Graphite Containing Natural Anhydrite

This study examined the effect of natural anhydrite (CaSO4) powder additions on the microstructure and frictional properties of a 95 Bronze - 5 Graphite composite prepared by a powder metallurgy process. Natural anhydrite powder, ranging in content from 2 to 8 weight percent, was added to a premixed bronze powder composed of copper and tin and mixed, before the graphite was added. The powder mixture was compacted into disc shaped samples under a pressure of 500 MPa. The compacted samples were sintered at 750 °C for 30 minute in a reducing atmosphere. The green and sintered densities of the samples were measured. A microstructural analysis of the sintered samples was also performed. It was found that the green density of the samples decreased with increased anhydrite content. The sintered densities were lower than the green densities due to sample expansion. A finer microstructure was observed in the samples containing anhydrite. The anhydrite additions resulted in the reduction of both the friction coefficient and wear of the bronze-graphite samples. The amount of anhydrite from 2 to 8 weight percent clearly altered the microstructure of the bronze-graphite samples, however, the level of reduction of the friction coefficient and wear were quite similar among the anhydrite containing samples.

Effect of Compaction Pressure and Sintering Time on the Properties of Sintered Cu-10Sn Bronze

Bronze-based composite materials are well known for use as friction materials. They are produced by powder metallurgy techniques from bronze powder, which acts as a matrix, and various friction modifying additives. The objective of this work was to study the effect of compaction pressure and sintering time on the properties of the unmodified bronze matrix. The bronze powder used was prealloyed with a composition of Cu-10Sn. The specimens were pressed by uniaxial die compaction with pressures of 282 to 339 MPa. The sintering experiments were conducted in an alumina tube furnace at 800 °C with sintering times of 30, 45, and 60 min under a vacuum pressure of 2.25x10-2 Torr. From the results, it was found that the density of the samples increased with increasing compaction pressure. A microstructural examination of the samples for the different sintering times showed them to look very similar. Finally, the highest sintered density of 7.30 g/cm3 was obtained at 800 °C for 60 min.