Improved lubrication and wear resistance of gallium-matrix liquid metal containing molybdenum diselenide nanoparticles under heavy load conditions

Abstract

Owing to their advantages of high load-carrying performance, efficient heat conduction, and low friction coefficient, liquid metal-lubricated spiral groove bearings are critical mechanical components in high-speed mechanical support systems including computed tomography X-ray tubes, machine spindles of multi-axis numerical control machining center, etc. Therefore, it is imperative to understand the tribological mechanisms between liquid metal lubricants and tribo-pairs aiming to improve their functional properties and extend the service life of spiral groove bearings. In this study, molybdenum diselenide (MoSe2) nanoparticles, a friction-reducing lubricant, were blended as an additive into the gallium-based liquid metal (LM, Ga64In24Sn12) using mechanical grinding techniques. Following lubrication with MoSe2/Ga64In24Sn12 LM lubricant, friction and wear characteristics of Si3N4 ceramics ball/AISI 52100 steel disk friction pairs were evaluated by a high-frequency linear reciprocating oscillation friction test machine with ball-on-disc configuration under a normal load ranging from 50 N to 1500 N. Experimental results demonstrate that as the MoSe2 dosage increases, the viscosity of MoSe2/Ga64In24Sn12 LM lubricant gradually rises. Both normal load and MoSe2 nanoparticles content have a notable influence on the lubrication properties of MoSe2/Ga64In24Sn12 LM lubricant at a light (50 N) or a heavy load (1500 N). Of all these LM lubricants, the best lubrication performance and wear resistance (f = 0.10, k = 1.93×10−8 mm3/Nm) was achieved for 5.0 wt% MoSe2/Ga64In24Sn12. The improvement in the lubrication characteristics of MoSe2/Ga64In24Sn12 LM lubricant under heavy load conditions originated from the generation of tribo-films from the Tribo-chemical reactions involving MoSe2 nanoparticles. The thickness of Ga-based tribo-films is 1.50 ± 0.10 μm. This kind of tribo-films is rich in various nanocrystals consisting of orthorhombic α-Fe2O3, monoclinic β-Ga2O3, cubic In2O3, tetragonal rutile SnO2, orthorhombic α-MoO3, and noncrystalline SiO2. Friction-induced lubricating films prevent adhesion wear of frictional pairs at heavy loads and consequently increase the load-bearing characteristics of LM lubricant, thereby improving the lubrication characteristics of LM.