This study reports a novel synergetic approach combining nano-lubrication and conventional extreme pressure additivation, to explore the tribological performance of piston ring/cylinder liner conformal contact. Three typical lubricating formulations, viz, (i) PAO (poly-alpha-olefin) base oil (ii) base oil with mild extreme pressure (MEP) additive, and (iii) base oil with composite blend of mild extreme pressure (MEP) additive and WS2 nano-particles, were investigated using an ASTM G-99 Standard customized universal tribometer for evaluating friction and wear behavior of coated chromium/bulk grey cast iron (CI) tribopair. The lubricant formulations were tested at engine working temperature of 200 °C, reciprocated under a normal load of 30 N, stroke length of 10 mm and a constant sliding velocity of 0.2 ms−1. Wear attributes were evaluated by employing non-contact based 3 D optical profilometry. For assessment of tribo-surface morphology and associated surface characterization, Elemental Dispersion Spectral (EDS) incorporated Scanning Electron Microscope (SEM) was utilised. Green Laser Raman spectroscopy investigated tribo-chemistry, synergetic interactions and tribo-film formations. A state approaching super-lubricity and ultralow friction was achieved by sliding grey CI (Plateau Honed) cylinder liner against electroplated chrome stainless steel top compression ring with PAO10 base oil ultrasonically dispersed with 1 vol% of Isopropyl phenyl Phosphate (IPP), a mild extreme pressure (MEP) triaryl phosphate additive & 1 wt.% of WS2. Results obtained therein demonstrated four dominating forms of wear on the cast iron surface, i.e. plowing wear, abrasive wear, adhesive wear and oxidative wear. Counterpart chromium surface exhibited plowing and abrasive wear only. This substantial friction and wear reduction are attributed to the coalesced intrinsic characteristics of MEP and IF-WS2 additives, thus improving the overall lubrication characteristics of base oil.

This research reports the scuffing failure phenomenon of piston ring-cylinder liner in pilot state bench tests. Initially, microhardness evaluation of chromium sprayed piston rings of functionally graded Aluminium A390 piston was conducted using a Vickers hardness Indenter following ASTM E-384 standard. The tribological characterization for dry sliding, simulating lubrication starvation was evaluated using reciprocating Universal Tribometer. For surface morphology and allied surface characterization, Energy Dispersive X-Ray spectroscopy integrated Scanning Electron Microscope was used. Substantially large volumes of wear depicting abnormal wear have been observed on the tribo-conjugate grey CI cylinder liner surfaces in sliding with chromium coating on SAE9254 grade steel substrate. This can be attributed to the considerable hardness gradient of tribopair in conjugation. With chromium coating having a conspicuous hardness edge over the CI cylinder liner, the extrusion and ploughing of the liner surface depict the abnormality in wear. The Coefficient of Friction (COF) under dry sliding with stepped load increments showed an unsteady state of friction and this performance is underrated for operation of any tribological system.