Advanced Tribological Characterization of DLC Coatings Produced by Ne-HiPIMS for the Application on the Piston Rings of Internal Combustion Engines

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.

Improvement of corrosion resistance and mechanical properties of chrome plating by diamond-like carbon coating with different silicon-based interlayers

“…DLC films can be used in the magnetic data storage industry for the protective coating of magnetic storage disks and their read/write heads [6]. In the automotive industry, DLC films are applied to the piston ring and cylinder block to reduce the wear rate with constant abrasion and extend the service life [7]. Due to the high atomic density of DLC films, they are used in the food packaging industry as a coating on PET bottles, fresh and dry food packaging to act as a gas diffusion barrier and extend the shelf life of food [8].…”

A review on preparation process and tribological performance of coatings for internal combustion engine piston ring

“…In order to improve the tribological properties of piston rings, Vahidi et al 37 deposited DLC coatings by high-power impulse magnetron sputtering (HiPIMS). It was found that DLC coating had better tribological properties than CrN coating no matter under mixed lubrication or under hydrodynamic lubrication condition.…”

Tribological Behavior of Doped DLC Coatings in the Presence of Ionic Liquid Additive under Different Lubrication Regimes

“…The hydrodynamic and mixed lubrication regimes in internal combustion engines dominate the contact between the piston ring and cylinder liner for the most part, but a boundary lubrication regime is frequently found at the top dead center of the stroke, which necessitates the implementation of coatings. Polyalphaolefin (PAO) 8 was selected as the base lubricating oil because it serves as the base oil for various commercial engines [34,37,38]. Trihexyltetradecylphosphonium bis (2-ethylhexyl) phosphate [ P 66614 ] [DEHP] ionic liquid was used in this study.…”

“…As a counterpart, an AISI 3415 steel ring (often used for cylinder liners) with a diameter of 115 mm and width of 12 mm was used. The ring surface was polished with 2000 granulometry sandpaper to resemble the surfaces frequently employed in internal combustion engines [34]. Then, with the help of a profilometer, the surface roughness was measured.…”

“…PAO 8 is a highly branched lubricant used in the automotive industry, and a few investigations have been carried out to improve its tribological performance in lubricating DLC coatings (DLC coatings are also widely used in the automotive industry due to their favorable tribological properties) [33][34][35]. On the other hand, even though previous investigations have shown that lanthanides, including Eu (europium) and Gd (gadolinium), have a high affinity for ILs and, in some cases, ILs have even been used for the recovery of rare-earth metals [18,19,36], their potential advantage for improving the tribological interaction between lanthanide-doped DLC thin films and ILs has not been thoroughly investigated.…”