Tribological performance of high-strength cast iron in lubricated contact containing carbon black

Abstract

Abstract It is well-known that diesel engines generate soot during the combustion process, leading to a higher level of pollutant emissions and severe wear of contact surfaces in relative motion, resulting in worse engine performance. Carbon black has been used in laboratory wear tests to simulate soot in engine components such as piston rings and cylinder liners. However, there are still many questions to be answered, especially concerning the interaction between the particles, lubricants, and surface topography in contact. In the past years, compacted graphite iron (CGI) has been substituting grey cast irons in engine blocks because of its improved mechanical properties, resulting in thinner walls for lighter blocks and improving engines performance. However, CGI s tribological behavior of higher strength grades has been scarcely studied due to its production cost and complexity. In the present study, two CGIs of high strength (JV450 and JV500 – ISO 16112/2017) were used as cylinder liners on ring-on-cylinder lubricated wear tests a CETR-UMT-Bruker tribometer. The cylinders surfaces were honed to a plateau finishing, and the counterbody used was a commercial compression ring of nitrided stainless steel. Carbon black particles were added to commercial SAE CF-30 lubricant, simulating the presence of soot. The testing load and oil temperature were 175\xa0N and 100\xa0°C, respectively, creating a severe wear condition. Roughness measurements using interferometry were performed on the worn surfaces to compare with the plateau s topography and roughness parameters honing texture. The variation of structure height was used as the indicative of liner wear. Results showed almost the same coefficient of friction (COF) for all tested conditions. Still, the reason for each case was different, the ejection of graphite during sliding being more critical for JV450 iron. The carbon black was able to change the contact conditions. The high-strength GJV500 iron performed better, considering a tribological merit index (TMI), less sensitive to the presence of carbon black in the lubricant oil.