PVD Deposition of Nb-MoS2 Coatings on Gear Carburized Steel

Abstract

© 2023 the authors.In recent years, the automotive sector has shown a trend toward electrification in all segments. The introduction of the electric motor brings with it a set of new challenging requirements for the transmission system, which can potentially be addressed by coatings technology. Doping MoS2 coatings with transition metals have recently received great attention in many engineering areas due to their unique optical, electrical, and excellent lubricating properties. These novel composite coatings are acclaimed for improving tribology performance under sliding-rolling conditions, especially with Ti doping. The focus of this research will be the replacement of Ti as dopant element by Nb, which presents similar physical properties and promising results in terms of its application as self-lubricant coating, according to few previously reported studies. In this work, investigations of MoS2-based coatings innovative doped with Nb obtained via PVD magnetron sputtering process considering different deposition parameters and substrate surface integrity were studied for gear applications. A deposition system with independent high-purity targets was used to obtain coatings with tailored microstructural, mechanical, and tribological properties. Some tests were performed to determine the coating microstructural and mechanical properties, the adhesion on carburized SAE 8620 steel samples, commonly used for gear applications, and also the influence of the substrate residual stress state on coating behavior. Preliminary results suggest a significant influence of the metal doping content on the mechanical and tribological properties of the coatings. The obtained coatings showed lower coefficient of friction and proper adhesion on carburized SAE 8620 steels, also influenced by the substrate surface integrity. Moreover, the results suggest that further studies on Nb:MoS2 coatings for transmission systems applications are promissory to enhance the durability and efficiency of gears.