Influence of Manufacturing-Induced Residual Stress of Substrate on Coating Performance for Gear Applications

The mobility sector has shown a trend toward electrification in all segments. The introduction of the electric motor brings a set of new challenging requirements for the gears of the transmission system. Coatings represent a promising technology for addressing these challenges, providing gear systems with higher torque efficiency, contact fatigue strength, wear resistance, and even NVH emission reduction. However, despite the potential benefits of coatings, there remains a significant knowledge gap regarding how substrate surface integrity influences the overall performance of the coated gear system. The objective of this study is then the comprehension of the interaction between MoS₂-based coating and substrate surface integrity. For this, case-hardened steel samples were manufactured with different grinding parameters, which induced different surface integrity states, followed by coating deposition with the same parameters. The substrates with different manufacturing-induced surface integrities were characterized in terms of residual stress state, topography, microhardness, and microstructure. Given its economic advantage at a national scale, Nb was used as MoS2 dopant, and the results showed that the strategic metal improves the coating properties. The virtually identical coatings, deposited on substrates with distinct surface integrity properties, were comparatively tested and showed different tribological behavior. Such results highlight that designing a PVD-oriented manufacturing chain can improve the coating performance, leading to gear mechanical systems with reduced energy losses.