Structure and properties of powder gas-plasma coatings based on nickel

Abstract

Problem. The development of modern technology requires a constant increase in reliability and durability of products. Widely used in the practice of domestic and foreign engineering coatings from electrolytic chromium for several hundred hours are triggered, they are unsatisfactorily working on friction and wear at high temperatures. The subject of the study were powder materials based on nickel PG-SR 3 and PG-SR 4. The work is devoted to the study of the formation of gas-plasma coatings on parts of the cylinder-piston group of internal combustion engines using self-fluxing powders based on nickel, as well as the structure and properties change after coating sputtering, its reflow, subsequent hardening. Goal. The purpose of this work is to study powder materials applied to the working surfaces of piston rings by gas-thermal spraying. The object of the study are processes of formation of the structure and properties of coatings from powder materials. Methodology. Plasma sputtering modes were carried out with the following constant parameters: sample rotation speed - 45 rpm, linear speed of sample movement relative to the plasma jet - 18.4 m/min; the diameter of the charge line in the anode nozzle is 2 mm; the distance from the place of introduction of the powder to the cut of the nozzle is 4 mm; the axis of the plasma jet is perpendicular to the axis of rotation of the sample. Radiographically, a multiphase structure is registered in the initial powder. The most fully presented solid solution lines based on nickel and carbide phase Cr23С6 type. But many lines cannot be clearly identified. A match can be found with the main lines of chromium and nickel borides, chromium silicides. The X-ray pattern of the fused layer quite completely coincides with the X-ray pattern of the powder. Chromium carbide lines and the strongest lines of other phases are preserved on the radiograph of the unmelted layer. Preservation of phase lines in the deposited layer without reflow and the layer after quenching indicates that these phases are formed during primary crystallization. This is confirmed by the metallography of the original powder and the original layer. In the structure of the powder, crystals are visible, as well as a dispersed mixture of phases between them. Electron microscopic studies show that in the area of coarse mixtures, oriented areas are observed, in the area of fine mixtures - non-oriented, less dispersed. Results. The presence in the deposited layer of a solid solution based on nickel, carbide phase, borides of chromium and nickel, chromium silicides is established. The greatest macro- and microhardness is possessed by fused layers containing the greatest number of strengthening phases. Originality. Gas-thermal sputtering of powder materials applied to the working surfaces of piston rings is used, which significantly increases their operational properties in comparison with other methods. Practical value. The conducted researches and industrial tests allowed to introduce the coating into production. Conclusions. As a result of the conducted researches on surfacing and heat treatment of coatings made of PG-SR powders, it was confirmed that the best properties have fused coatings. For coatings made of PG-SR powders, heat treatment is undesirable, as it deteriorates the structure and properties of the coating.