Tribological behavior of chrome-deposited SAE9254 grade steel top compression piston ring under lubrication starvation and mild extreme pressure lubrication

This article reports tribological studies of piston ring/cylinder liner tribo-contact to evaluate the scuffing failure under dry sliding conditions and its minimization with mild extreme pressure lubrication. The tribological conjugation tested employs a piston ring of SAE9254 grade steel substrate with plasma-sprayed chromium coating of 42 µm and ISO R185220 grade gray cast iron cylinder liner. A conformal, cylinder inscribed in cylindrical cavity contact was ensured to simulate actual dead center reciprocating between piston ring–cylinder liner interface. Tribotests were conducted under dry sliding, simulating lubrication starvation and sliding in extreme pressure additivation blend at a temperature of 200 °C with 10 mm stroke length and reciprocating velocity of 0.2 m s–1. The friction characteristics of the piston ring and cylinder liner samples in cited test conditions were studied as a function of load and continuously monitored throughout the tests. Optimal profilometry was employed for evaluating wear attributes. For surface morphology and allied surface characterization, energy-dispersive X-ray spectroscopy integrated scanning electron microscopy was used. For tribo-chemical interactions and film formation, the tribo-surfaces were further investigated with Raman spectroscopy. ASTM E-384 standard Vickers indentation microhardness and its precedence to tribological characteristics were evaluated. The extreme pressure lubrication is intended to potentially improve the scuffing résistance and optimization of coating material in achieving superior tribological characteristics. Superior lubricity, scuffing resistance and enhanced load-bearing capacity attributes were manifested by EP-PAO10 blend lubrication contrasting the surface deteriorations and scuffing failure ascribed to dry sliding.