Industrial Gear Oils: Tribological Performance and Subsurface Changes

Abstract

This study examined the tribological performance of three gear oils (Oils A, B and C), in relation to surface and microstructural changes. Oil A contains molybdenum dithiophosphate friction modifier, Oil B contains amine molybdate combined with zinc dialkyl dithiophosphate antiwear additive, while Oil C contains phosphonate and a commercial gear oil package. Following sliding tests of a hardened AISI 52100 steel ball on a spheroidized AISI 52100 steel disc, the worn surfaces were chemically studied using Raman and energy-dispersive X-ray spectroscopy. The tribological performance for each oil was different, likewise the nature of the tribofilm formed. After a 5 min sliding test, the hardness-depth profile of the worn surfaces was measured; also the cross-sectional microstructure was examined using scanning electron microscopy combined with focused ion beam preparation and transmission electron backscattered diffraction (t-EBSD) techniques. With Oil A, there was a relatively small increase in surface hardness (33% greater than that of the unworn surface), whereas with Oils B and C, the average hardness near the surface was 100% greater than that of the unworn surface. The cross-sectional microstructure using Oil A also differed from Oils B and C, which were quite similar. The result shows that with Oil A refinement of the ferrite grains spreads deeper into the material (> 10 µm), whilst with Oils B and C it was largely limited to 2–3 µm below the surface. It is concluded that the lubricant formulations and their associated tribofilms influenced the extent of deformation in the subsurface layers and consequently influenced the wear performance.

Industrial Gear Oils: Influence of Bulk Oil Temperature and Contact Pressure on Tribological Performance and Subsurface Changes

“…Besides the general increase in surface hardening with temperature, hardness profile of Oil A appears to be distinct from that of oils B and C which was similarly observed in our preliminary study [20]. The unworn microstructure of the steel disc (speriodized AISI 52100 steel) consists of cementite particles (FeC) embedded in large ferrite grains (see Fig.…”

“…Fatigue of this layer can lead to the formation of wear debris. In a previous study [20] we studied the relationship between tribological performance of the industrial gear oils and subsurface mechanical and microstructural changes. The study concluded that the gear oil formulation and their associated tribofilm influenced the extent of subsurface deformation and consequently influenced the wear performance.…”

Classification of Lubricating Oil Types Using Mid-Infrared Spectroscopy Combined with Linear Discriminant Analysis–Support Vector Machine Algorithm

“…Lubricating oil mainly comprises basic oil, which governs its basic properties, and additives that enhance the performance of basic oil, providing certain new functions [7]. As seen from data shown in [8][9][10][11][12], lubricants with different types of additives are supposed to lead to different effects.…”

Tribological performance of organic molybdenum in the presence of organic friction modifier

“…Syngernistic tribological effect could be produced when MoDTC is mixed with zinc dialkyldithiophosphate (ZDDP). The research results indicate that the lubricant formulations and tribo-chemical reaction films could make a difference to the deformation of subsurface layers, which plays an important role in the anti-wear performance [ 9 ]. Syngernistic tribological effect could also be found when mixing sulfur- and phosphorus- free molybdenum amide (MA) with ZDDP [ 10 ].…”