Influence of Sintered Low-Alloy Steel Microstructure on the DLC Coating Characteristics

Abstract

In this study, the effect of base steel microstructure on the white layer was obtained by plasma nitriding and DLC coating investigated. For this purpose, sintered iron-based steel containing molybdenum (based Astaloy Mo) was used. The steel powders were formed by the hydraulic press and sintered in the NH3 atmosphere. After that, samples were cooled with two different cooling rates (0.5 and 3 °C/s). Then, the samples were plasma-nitrided. After that, the DLC coating was applied and sliding tests were done under 60 and 90 N normal load. It was found that the microstructure differences were obtained because the cooling rate had a significant effect on the roughness, coating thickness, and ratio of the phases in the white layer, and these changes affected the DLC coating. So, the wear and mechanical behavior of the coating of the two samples had different properties. It was observed that mass loss approximately changed 75% by increasing the cooling rate. Pulling out, burnishing, cracking, and oxidation were the main mechanisms of the DLC coatings deposited on the substrate, while in sinter-hardened sample (cooling rate 3 °C), more surface damage was observed. Hardness test, SEM analysis equipped with EDS, RBS and nanoindentation test were used to evaluate DLC coating.