Migration-Lubrication Performance at Friction Pair Interfaces under Temperature-Velocity Fields

Thermally driven creeping (also known as creeping or migration) refers to the behavior in which lubricant spreads directionally from a high-temperature area to a low-temperature area at the friction interface without external forces. In the rolling bearings of space mechanisms and precision instruments, lubricant creeping and loss increase frictional resistance, which in turn affects the operational accuracy of the system. Friction and wear are inevitable in mechanical motion, and the heat generated by friction leads to the formation of a temperature gradient on the surface of the friction pair. In extreme operating conditions, liquid lubricants are easily affected by surface tension, and even a small temperature gradient can cause lubricant to creep and migrate. In modern mechanical industries, the problem of lubricant creeping loss is common in bearings. During operation, the high temperature of the bearing raceway causes the lubricant to creep and migrate to the lower-temperature outer regions of the raceway, significantly reducing the bearing’s lifespan, leading to lubrication failures in mechanical equipment, and lowering production efficiency. This study used point-to-surface contact friction pairs consisting of typical rolling bearing balls made of GCr15 and Si₃N₄ and a 304 stainless steel flat surface, exploring the thermally driven creeping behavior and lubrication characteristics of lubricants under the combined effects of temperature gradients and interface motion. The study examined the changes in friction force under horizontal and vertical temperature gradients, including dry friction, silicone oil lubrication and different temperature gradient directions. The impact of roller diameter, roller material, and temperature gradient direction on friction and lubrication performance was also analyzed. The study introduced gravity as a factor and investigated how friction force changed when the gravity direction aligned or opposed the temperature gradient direction. It also observed the variation in contact angle during friction motion. The results showed that under the same experimental conditions, the friction force variation pattern was consistent for balls of different diameters. When the temperature gradient was perpendicular or parallel to the motion direction or vertical, the friction force changed inconsistently during reciprocating motion, exhibiting “symmetric” and “asymmetric” phenomena. When the temperature gradient direction was the same as the gravity direction, it accelerated the thermally driven creeping of silicone oil. However, when the temperature gradient direction opposed the gravity direction, it inhibited the thermally driven creeping of silicone oil. Further analysis revealed the effect of the creeping direction on friction force and contact angle variation. This research uncovered the mechanisms behind the differences in interfacial thermally driven creeping and tribological behavior under the synergistic effects of temperature and velocity fields. The findings were expected to provide valuable insights for designing durable localized lubrication in special operating conditions for space mechanisms and precision instruments. Additionally, it was expected to support the miniaturization, efficiency improvement and reliability enhancement of complex mechanical equipment, offering important guidance for advancing the design standards of high-end aerospace equipment.