| Resumo : |
The electrification of propulsion systems has attracted attention due to its potential to mitigate environmental impacts. Therefore, gear systems face challenges such as high torque and speeds, low noise, and low friction due to the critical role of torque efficiency in vehicle autonomy. However, there remain knowledge gaps regarding the influence of substrate surface integrity on coating behavior. The objective of this study is then the comprehension of the interaction between MoS2-based coating and substrate surface integrity for application in low-friction gear systems. The investigation begins analyzing the impact of adding coating-related processes to the gear manufacturing chain in terms of the surface integrity state. Properties of substrate surface integrity state that affect coating behavior are then explored. Finally, the findings obtained in both approaches are extended to fatigue testing of coated gears. Surface preparation methods prior to deposition showed significant differences in the resulting surface integrity state. Coating deposition preserved the initial topography and induced compressive residual stresses in the substrate, counteracting the expected relaxation due to the thermal input of the process. Substrate topography played a crucial role in coating behavior, with rougher surfaces improving adhesion and exhibiting a lower and more stable coefficient of friction. However, coatings deposited on substrates with high compressive residual stresses showed poor adhesion, likely due to stress mismatches at the substrate-coating interface. Fatigue tests revealed increased lifetimes for coated gears. A detailed analysis suggests these results are more closely associated with the surface integrity state induced by surface preparation and deposition methods rather than the coating itself. These processes promoted lower roughness in both coated conditions and high compressive residual stresses in one, contributing to higher durability. The obtained findings confirm the potential of coatings for low-friction applications, such as electric mobility gears, as well as the key role of substrate surface integrity state in adequate coating behavior. As a next step, these results should be validated in industrial environments. |