Determination of Adhesive and Cohesive Strength in Metal Coatings Deposited by Hypersonic Metallization

. It is known that at present, methods of thermal spraying are widely used to restore and strengthen various worn-out machine parts. As a rule, metal coatings applied by thermal spraying have lower strength characteristics than solid materials. It is believed that the strength of coatings is proportional to their adhesive and cohesive strength. The value of adhesive and cohesive strength depends on various factors, including the nature of the materials and the technology of coating. An important factor characterizing the possibility of using metal coatings in various industries is the strength of adhesion of coatings to the base metal. The paper presents the determination of the adhesive and cohesive strength of coatings from different materials, applied by the method of hypersonic metallization. The results of testing the strength of metal coatings made of ER316LSi-grade wire, nichrome (Cr20Ni80) and molybdenum wire are given in the paper. Based on the results of metallographic studies, the proportion of the participation of cohesive and adhesive components in the strength of coatings has been determined, and some features of coating destruction have been described. It has been found that the participation of the cohesive and adhesive components of the coating strength differs depending on the material used. The cohesive component prevails in the strength of coatings made of high-alloy wire of the ER316LSi-grade, at which destruction mainly occurs along the coating-base boundary. For nichrome coatings and especially for coatings made of molybdenum, the cohesive component is predominant, in which the destruction of the coating occurs not along the coating-base boundary, but between the coating layers.

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.

Enhancing the Fire Resistance of Concrete Structures by Applying Fire-Retardant Temperature-Resistant Metal Coatings

The issues relating to an increase in the fire-resistance of concrete structures by applying (heat dissipating) fire-retardant and fire resistant metal coatings onto them was considered. The experimental investigation data obtained for the heating rate of the brick coated with the aluminum layer as heat dissipating coating were given. The investigation was carried out through the comparison of a time-dependent change in the temperature of the material coated with the aluminum layer with the temperature of uncoated material. The obtained research results proved a decrease in the heating rate of the coated brick exposed to the thermal irradiation.

New Technologies for Producing Multifunctional Reinforced Carbon Plastics

In this article we investigated properties of elementary carbon fibers after their activation and subsequent deposition of thin layers of metal coatings on their surface. For deposition we used copper, titanium and stainless steel. We investigated influence of various technologies of preliminary processing of the fiber surface on the value of the adhesion strength of the metal coating to the carbon tape and on the mechanical properties of elementary fibers. We established that the strength of carbon plastics at interlayer shear increases by 10-30% when using carbon tapes and fabrics with a metal coating.