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

Abstract

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.

Gas flow through a bore-piston ring contact

“…[28][29][30][31] Few works dedicated to this issue addressed the problem from a tribological point of view. [22][23][24][25] Figure 1 shows that the ring defects should also be taken into account since they can induce an aperture of several hundredths of millimeters. They shall certainly be considered as the main origin of poor conformity.…”

“…The flow is actually incompressible, as shown by equation (24), and in the creeping regime, as indicated by equations (22). The momentum equations can then be integrated.…”

“…Experimental observations confirm this assumption and clearly show that the mechanism is enhanced by excessive bore distortions. 20,21 Nevertheless, the literature dedicated to the analysis of the rings to bore conformity is mainly focused on tribological aspects [22][23][24][25] and the gas flow mechanism through the aperture field has not been enough reported with enough details.…”

Insights into the tribological behavior of IF-WS2 nanoparticle reinforced mild extreme pressure lubrication for coated chromium/bulk grey cast iron interface

“…24 Over past three decades, triaryl phosphates, phosphate additives and metal thiophosphates has been extensively used as EP additives in various lubrication formulations. 25 Phosphate esters, in particular Triaryl phosphates (TPs) have emerged as front runners in minimization of friction and wear subjected to boundary lubrication working. Phosphate esters demonstrate active chemical affinity to iron oxides rather to naive elemental state iron on steel substrates.…”

“…Phosphate esters demonstrate active chemical affinity to iron oxides rather to naive elemental state iron on steel substrates. 25,26 One tribo-counterpart i.e., grey CI liner surfaces are chemically susceptible to iron oxide formation under moist air suction charge and hence pave a stable oxidation reaction medium to TPs resulting Iron Polyphosphates. The oxidation reaction end products synergetically result in lubricant film formation with a considerable wear reduction and ultimately resulting in the intended EP lubrication action.…”