To develop high-performance lubricants, this study investigates polyamide 6 (PA6) as a solid additive in urea-based greases (UBGs). The tribological performance of UBGs containing varying concentrations of PA6 was evaluated at different temperatures using an HSR-2 M high-speed reciprocating friction and wear tester. The structure and composition of PA6 and the worn surfaces were characterized using scanning electron microscopy, thermo-gravimetric analysis, Fourier transform infrared spectroscopy, 3D laser scanning microscopy, X-ray photoelectron spectroscopy, and focused ion beam techniques to elucidate the underlying friction and wear mechanisms. The results demonstrate that PA6 significantly enhances the lubricating performance of UBGs. At an optimal concentration of 0.2 wt% PA6 and 40 °C, the friction coefficient was reduced by 7.6%, and the wear volume decreased by 50.9% compared to base UBG. This improvement is attributed to the formation of a tribofilm on the steel surface, driven by interactions between PA6 microspheres and the grease matrix. Upon contact, PA6 adsorbs and deposits on the steel surface, promoting the formation of a continuous lubricating film. This film enhances the film-forming capacity of the base grease, minimizes direct ball–disk contact, and effectively reduces friction and wear.

Tribological behavior and mechanism of polyamide particles in urea-based grease at different temperatures
    Abstract
    1 Introduction
    2 Experiments
        2.1 Preparation of PA6/UBG additive
        2.2 Analysis methods
    3 Results and discussion
        3.1 Physicochemical characterization of PA6
        3.2 Tribological properties of PA6/UBG additive
        3.3 FESEM/EDS analysis of wear scars
        3.4 Friction and wear mechanisms
    4 Conclusions
    References

• Yijun Chen(Huangshan Shangyi Rubber and Plastic Products Co., Ltd, Huangshan 245500, China)
• Chuan Li(School of Chemistry and Material Engineering, Chaohu University, Hefei 238000, China, Huangshan Shangyi Rubber and Plastic Products Co., Ltd, Huangshan 245500, China)
• Wenqi Zhang(School of Chemistry and Material Engineering, Chaohu University, Hefei 238000, China)
• Zhilin Fang(School of Chemistry and Material Engineering, Chaohu University, Hefei 238000, China)
• Shike Chang(School of Chemistry and Material Engineering, Chaohu University, Hefei 238000, China)
• Xiaodong Wang(School of Chemistry and Material Engineering, Chaohu University, Hefei 238000, China)
• Xiaoyong Xu(School of Chemistry and Material Engineering, Chaohu University, Hefei 238000, China)
• Xu Tan(School of Chemistry and Material Engineering, Chaohu University, Hefei 238000, China, Department of Energy Materials and Chemical Engineering, Hefei University, Hefei 230601, China)
• Enzhu Hu(Department of Energy Materials and Chemical Engineering, Hefei University, Hefei 230601, China) Corresponding author