Tribological characterization of a bearing coated with UHMWPE/GNPs nanocomposite coating

Abstract

Polymer nanocomposite coatings with low friction and high wear resistance are being developed to protect aluminium surfaces against wear and tear during dry and boundary lubrication. In the present study, pure and graphene nanoplatelets (GNPs) reinforced ultra-high molecular weight polyethylene (UHMWPE) nanocomposite coatings are deposited on aluminium thrust bearings. Each bearing makes an ROD contact with a metallic disc counterface to simulate the contact configuration in an actual bearing. A set of tests involving pure and reinforced UHMWPE coatings under dry and liquid contact lubrication is conducted. The wear test results reveal that UHMWPE/1 wt-% GNPs performs better than the reference sample significantly. It reduces the friction and wear of aluminium both in the dry and boundary lubrication conditions at different conditions. The 1 wt-% GNPs reinforcement increases the load-bearing capacity of UHMWPE by 440% in the presence of base oil.

Recent Advances in UHMWPE/UHMWPE Nanocomposite/UHMWPE Hybrid Nanocomposite Polymer Coatings for Tribological Applications: A Comprehensive Review

“…Ismaila et al [ 69 , 70 , 71 ], used different concentrations (0.25, 1 and 2 wt.%) of graphene nanoplatelets (GNPs) to reinforce UHMWPE and deposited the nanocomposite coating on air plasma treated aluminum substrates using electrostatic spraying technique. Pin-on-disk wear tests were conducted using a hardened tool steel pin to optimize the loading of GNPs.…”

“…The optimized coating was further tested at different loads and different sliding speeds to determine the operating limits of the coating, which was found to be 4 MPa m/s [ 69 ]. Further to this study, Ismaila et al [ 70 ] proceeded to coat aluminum thrust bearings in the form of a ring, to simulate the actual conditions and tested the coatings using a ring-on-disk tests against a steel disk. The tests were carried out under dry and base oil lubricated conditions.…”

“…Substrates were placed in a Harrick Plasma Cleaner/Sterilizer under vacuum at an RF power of 30 W for approximately 5 min. Air-plasma treatment has been found to be an effective pre-treatment method, which is environmental friendly, easy to use, very flexible/adaptive, cost effective and less time consuming [ 60 , 61 , 62 , 63 , 64 , 66 , 67 , 68 , 69 , 70 , 71 , 72 ]. Air-plasma treatment helps in cleaning the surface by carbon cleaning effect and at the same time functionalizes the surface with carboxyl and hydroxyl groups which in turn increases the wettablility/surface free energy of the surface leading to an improved adhesion between the coating and the substrate.…”

“…Nanopowders for electrostatic spray coating : The electrostatic spray coating technique has been used by [ 68 , 69 , 70 , 71 , 72 ], to deposit the coatings on steel and aluminum substrates. The nanopowders were prepared by ultrasonicating the required amount of fillers in 50 mL of ethanol using a probe sonicator with an amplitude of 30% and a cycle on/off time of 20/5 s for 10 min followed by magnetic stirring for 2 min to ensure uniform dispersion.…”

“…Electrostatic spray coating process : Electrostatic spraying is excellently suitable for conductive materials. It’s a very efficient, cost effective, simple and a flexible/adaptive technique, used by researchers to deposit UHMWPE coatings on metallic substrates [ 68 , 69 , 70 , 71 , 72 ]. The basic principle of electrostatic spray gun is that negatively charged powder particles are deposited on positively charged substrate.…”