Assessment of Tribological Properties of Oil-Based Flake WS2-Oleic Acid Lubricant on Steel-Brass Sliding Contact

Abstract

The current research focused on the tribological properties of flake-like WS2 particles dispersed into PAO4 base oil with oleic acid as surfactant. Various concentrations of 0.2 mass%, 1 mass% and 3 mass% were applied in the preparation of WS2-OA lubricant. The wear tests were carried out using a ball-on-plate reciprocating sliding test configuration. It was found that the highest COF of 0.578 was obtained using PAO4 base oil with significant fluctuations. The COF could be reduced to approximately 0.34 and stabilized after adding the OA. When introducing the WS2 articles, the COF was around 0.158 under 0.2 mass%, 0.143 under 1 mass% and 0.145 under 3 mass%, and became almost constant after 4 min. In addition, the highest wear rate in width of 61.5 µm/m and in depth of 2.2 µm/m was found using PAO4 base oil. The wear rate can be reduced to 51.6 µm/m in width (16.1%) and 0.9 µm/m (59.1%) in depth under 3 mass% OA. While using the WS2 particles, the wear rate in width could be further reduced to 45.2 µm/m using 1 mass% but with slightly higher wear rate in depth than that of OA. Based on the analysis in SEM and EDX, the abrasive grooves became less after introducing the OA, some dark spots composed of carbon acted as tribo-films on the worn area. While using WS2 particles, it could be found that WS2 flakes were adhered on the surfaces to reduce the friction and wear.

Keywords

• flake ws2 particles
• oleic acid
• steel-brass contact
• friction reduction
• anti-wear behavior