机械工程系

Dept of Mechanical Engineering

Breakthrough in extreme pressure lubrication has been achieved in Prof. Yu Tian’s group at Department of Mechanical Engineering

Frictional heat is a universal phenomenon. People utilized frictional heat from the ancient drilling wood to make fire to modern friction welding in aerospace industry. In industry, friction usually dissipates lots of energy and might cause the damage of friction pairs and machines. Sliding between two objects under very high load generally involves direct solid–solid contact at molecular/atomic level, the mechanism of which is far from clearly disclosed yet. Those microscopic solid–solid contacts could easily lead to local melting of rough surfaces. At extreme conditions, this local melting could propagate to the seizure and welding of the entire interface, called scuffing, which may lead to catastrophic results to mechanical systems. Therefore, the mechanism and its control of the energy dissipation in friction have been widely and profoundly explored.

Traditionally, the microscopic solid–solid contact is alleviated by various lubricants and additives based on their improved mechanical properties. In a standard four-ball test of the extreme pressure lubrication property of general lubricants, they can usually stand a load of about 2-3 kN, a few can reach 5 kN. In this work, Prof. Tian’s group realized the state-of-the-art of extreme pressure lubrication by utilizing the high thermal diffusivity of liquid metal, 2 orders of magnitude higher than general organic lubricants. The extreme pressure lubrication property of gallium based liquid metal (GBLM) was compared with gear oil and poly-α-olefin in a four-ball test. The liquid metal lubricates very well at an extremely high load (10 kN, the maximum capability of a four-ball tester) at a rotation speed of 1800 rpm for a duration of several minutes, much better than traditional organic lubricants which typically break down within seconds at a load of a few kN. Our comparative experiments and analysis showed that this super-extreme pressure lubrication capability of GBLM was attributed to the synergetic effect of the ultrafast heat dissipation of GBLM and the low friction coefficient of FeGa3 tribo-film. The present work demonstrated a novel way of improving lubrication capability by enhancing the lubricant thermal properties, which might lead to mechanical systems with much higher reliability.

The results have been published on ACS Applied Materials & Interfaces 2017, 9, 5638-5644, titled as” State-of-the-Art of Extreme Pressure Lubrication Realized with the High Thermal Diffusivity of Liquid Metal”. Post-doc Haijiang Li, and Dr. Pengyi Tian are the co-first authors of the paper. Collaborator of this work, Prof. Qunyang Li is the co-corresponding author.

This research is sponsored by the Natural Science Foundation of China with Grant Nos. 51323006 and 51425502.

Web link of this paper:http://pubs.acs.org/doi/abs/10.1021/acsami.6b15825

Fig A Temperature rising at the bottom of four-ball test under the same friction power generation; B The simulated maximum temperature evolution of steel balls.