HIGH-TEMPERATURE OXIDATION, MECHANICAL, AND TRIBOLOGICAL PROPERTIES OF ELECTROPLATED Cr COATING ON STEEL AFTER ANNEALING IN 700∘C
Abstract
Although electroplated hard chromium coatings were extensively studied and applied in industry, the properties of the coatings after annealing at different temperatures were investigated insufficiently. In this work, the influence of heat treatment on the mechanical, tribological, and structural properties of chromium coating, electrochemically deposited on 38HN3MFA steel were investigated. A specific bath composition and deposition parameters were selected, which has been compared to the literature data. Parameter selections were based on data from military research industry and contain noticeably lower amount of sulfuric acid (1.2g/L), CrO3 (180g/L) and lower current density (25A/dm2). Coefficient of friction and coatings wear rate were measured by means of ball-on-disc method at the temperature of 30∘C, 200∘C, 500∘C, and 700∘C. The coefficient of friction has decreased from 0.71 for the temperature of 30∘C to the value of 0.5 for 700∘C due to the change of wear mechanism. Hardness of the as-received coating reaches the value of 11.4GPa and 9.5, 8.3, 6.4GPa for the samples after annealing in the temperature of 200∘C, 500∘C and 700∘C, respectively. The influence of heat treatment on structural properties of electroplated Cr coatings was studied by X-ray diffraction. Scratch test showed that layer is characterized by excellent adhesion with no adhesive rupture. Cr-coated 38HN3MFA steel exhibits reduced susceptibility to high-temperature degradation by 25%, basing on the mass lost measured at 900∘C.
