With the current use of bio-renewable fuel, the application of Ethanol in Flex-Fuel vehicles presents a very low CO2 emission alternative when the complete cycle, from plantation, fuel production, till vehicle use, is considered. In Brazil more than 80% of the car production is composed of Flex-Fuel vehicles. Due to the lower heating content of the Ethanol, more aggressive combustion calibrations are used to obtain the same engine power than when burning gasoline. Such Ethanol demands, associated with the continuous increase of engine specific power has lead to thermo-mechanical loads which challenges the tribology of piston rings.The ethanol use brings also some specific tribological differences not very well understood like fuel dilution in the lube oil, especially on cold start, corrosive environment etc. Under specific driving conditions, incipient failures like spalling on nitrided steel top rings have been observed. When running with Ethanol, Flex-Fuel engines present higher PCP and this peak occurs in a crank angle closer to the Top Dead Center. Such condition increases ring wear, scuffing risk and tribological conditions that may lead to cracks on the nitrided case and later spalling.This paper covers the top ring performance on flex-fuel engines on the tribology perspective. It is discussed how the ethanol use on Flex-fueled engines affects the top ring in terms of wear, scuffing, spalling and friction. For the evaluation of wear and spalling resistance, dyno engine tests are presented. On scuffing, block on ring tests were performed and a rank of ring coatings is presented. Top ring friction behavior and its impact on fuel consumption are also discussed. Test results on engine floating liner are presented. Finally, ring technical solutions to overcome these challenges are discussed. Among them, steel piston ring with an improved nitriding treatment for increased toughness and a PVD coating to improve wear resistance and friction.It is presented several rig and engine tests to support the discussed technical solutions. Engine tests are based on an abusive procedure to evidence/anticipate the effects on performance caused by the unique characteristics of flex-fueled engines running with Ethanol.

Usually bainitic microstructures exhibit good toughness and austempering is typically the preferred heat treatment when toughness is the primary requirement of the component. Several reports have shown such characteristics when compared to tempered martensite. High-carbon steel may exhibit brittle characteristics but it is a good steel with respect to mechanical properties and wear resistance. The objective of this study was to compare the impact properties of AISI O1, a high-carbon tool steel, designated VND in Brazil. This was done by comparing Charpy impact strength under different heat-treatment cycles. Steel test specimens were quenched from 820°C and tempered at 450°C to obtain tempered martensite, then austenitized, cooled, and held at 350°C to obtain bainite by holding at temperature for 20, 40, and 60 min. Because hardness influences impact behavior, comparative studies were performed at the same surface hardness level. The austempered samples with bainite microstructures obtained at a constant temperature and, by varying holding times, exhibited lower impact properties as compared to the quenched and tempered condition.

This study investigates the influence of iron dilution on the microstructure and corrosion behavior of Inconel 625 weld overlays deposited on carbon steel. Different deposition strategies were employed to control dilution and to evaluate its effect on elemental segregation. The overlays were characterized in terms of microstructural evolution, chemical distribution, and corrosion performance under standardized testing conditions. The results show that increasing iron dilution enhances chemical segregation within the dendritic structure, which governs the initiation of localized corrosion. A critical dilution condition associated with the onset of pitting was identified. These findings advance the understanding of dilution-controlled corrosion mechanisms in nickel-based alloy overlays.