THE STRUCTURE AND PROPERTIES OF ELECTROPLATED CHROMIUM COATINGS WITH AN ULTRAFINE SUPERHARD FILLER
Problem Statement (Relevance): This paper discusses a method of increasing the resistance of electrolytic chromium. Objectives: The study is aimed at creating integrated electrochemical coatings. Methods Applied: The integrated electrochemical coating technology involves a coprecipitation of the metallic substrate and strengthening dispersion second-phase particles. The use of superhard materials, such as ultra-dispersed diamonds (UDD) and wurtzite-like boron nitride (γ-BN), as strengthening elements provides high-hardness, high-wear-resistance and low-friction integrated chromium coatings ensuring a longer part life. Originality: The article describes integrated electrochemical coatings with the thicknesses of up to 100 microns which have low fracture, high hardness and high wear resistance aimed at extending the service life of tools operating under severe load and wear conditions. This, in particular, refers to knife disks used for cutting sheet metal which have to be resharpened during the normal operation. Findings: The authors found that the UDD particles of up to 70 nm have the best penetration with regard to chromium coatings, with the predominant size of the boron nitride particles of 0.5 to 1 micron. The study shows that the UDD filler (6-70 nm) works more efficiently in coatings with the thickness of up to 50 microns, while the boron nitride filler, which is a coarser powder 0.1 to 10 microns in size, is more efficient in coatings with the thickness of 60 to 150 microns. The UDD nanoparticles show a better penetration in thin coatings producing a finer chromium crystalline structure. The gradual reduction of the hydrogen effect facilitates the integration of coarser strengthening particles, in particular the boron nitride microparticles. It was found that complex coatings comprising both UDD and γ-BN fillers offer a higher wear resistance. The combined effect of UDD particles and wurtzite-like boron nitride provides a 4-time increase in wear resistance compared with additive-free chromium coatings. Practical Relevance: The use of superhard materials, such as ultra-dispersed diamonds (UDD) and wurtzite-like boron nitride (γ-BN), as strengthening elements provides high-hardness, high-wear-resistance and low-friction integrated chromium coatings ensuring a longer part life [1-5].