Abstract
Piston rings (PR) are known for almost a quarter of the friction losses in internal combustion engines. This research work aims to improve the tribological performance of PR by a recently developed variant of Diamond-like Carbon (DLC) coatings deposited in a mixture of Ar and Ne plasma atmosphere (Ne-DLC) by high-power impulse magnetron sputtering (HiPIMS). For the benchmark, the widely used Chromium Nitride (CrN) and DLCs deposited in pure Ar plasma atmosphere (Ar-DLC) were used. The tribological tests were performed on a block-on-ring configuration under different lubrication regimes by varying temperatures and sliding speeds. The analysis of the results was performed by Stribeck curves corresponding to each sample. An improvement of the tribological performance was observed for Ne-DLC films by up to 22.8% reduction in COF compared to CrN in the boundary lubrication regime, whereas, for the Ar-DLC film, this reduction was only 9.5%. Moreover, the Ne-DLC films achieved ultralow friction of less than 0.001 during the transition to a hydrodynamic lubrication regime due to better wettability (lower contact angle) and higher surface free energy. Increasing the Ne up to 50% in the discharge gas also leads to an increase of hardness of DLC films from 19 to 24 GPa.
Highlights
The efficiency of an internal combustion engine (ICE) is an increasingly important concept nowadays, largely due to climate change and the need to reduce CO2 emissions into the atmosphere, trying, at all costs, to minimize the irreversible losses on our planet.the efficiency of an ICE is extremely important for the automotive industry, because the customers are looking for cars with less fuel consumption.It is estimated that a piston ring (PR) is responsible for about 24% of the friction losses in an ICE [1]
To reduce friction losses in PRs, studies have focused on the development of new materials, such as lubricants, surface textures or coatings to be applied to PRs, with the ability to reduce the coefficient of friction and improve the desired performance [3,4]
The grey cast iron’s maximum hardness can reach 250 HV (2.45 GPa) [25], which is much lower in comparison with the hardness of the coatings presented in this work
Summary
The efficiency of an internal combustion engine (ICE) is an increasingly important concept nowadays, largely due to climate change and the need to reduce CO2 emissions into the atmosphere, trying, at all costs, to minimize the irreversible losses on our planet. It is estimated that a piston ring (PR) is responsible for about 24% of the friction losses in an ICE [1]. Half of the friction losses from power cylinders are generated by PRs [2]. In this way, inevitably, the performance of an ICE is directly linked to the coefficient of friction generated by the contact of the PR with the cylinder liner [3]. To reduce friction losses in PRs, studies have focused on the development of new materials, such as lubricants, surface textures or coatings to be applied to PRs, with the ability to reduce the coefficient of friction and improve the desired performance [3,4]
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