image: To develop a wide-temperature-range superlubricity system, researchers first fabricated a uniform boronized layer via electrochemical boronizing. Based on the synergistic effect of the boronized layer and polyol lubricants, a superlubricable surface was constructed in-situ during the running-in stage, which was essentially a –(CH2–CH2)n– passivation tribofilm. At this stage, within the well-constructed superlubricity interfaces, a sufficiently thick lubrication film forms to support the friction pairs, which effectively reduces direct contact between the friction pairs and thereby achieves superlubricity behavior. Finally, an important factor in enhancing the extreme-temperature performance of superlubricity is the incorporation of a larger number of hydroxyl groups in the lubricant molecules, which leads to thicker lubrication films and reduces contact between the friction pairs, facilitating superlubricity at high temperatures.
Credit: ©Science China Press
Superlubricant materials and technologies can achieve near-zero friction and wear, attracting attention for their potential to reduce frictional losses. Since the concept of superlubricity was introduced in the early 1990s, it has evolved from atomic-scale structural superlubricity to macroscale liquid superlubricity. Liquid superlubricity at room temperature has gained significant attention, especially in water-based, glycerol-based, and ionic liquid systems that form ultra-low shear boundary layers under specific conditions. However, existing superlubricants fail to meet the demands of high-temperature applications, such as in aviation piston pumps where temperatures can reach 200 ℃. The stability of liquid lubricants is a key limiting factor, as higher temperatures reduce viscosity, weaken intermolecular forces like hydrogen bonds, thin the lubricating film, and increase friction. Additionally, current superlubricity technologies are typically limited to materials like diamond-like carbon films and mica, which are brittle and have poor adhesion, restricting their industrial applications.
The recent work published in Science Bulletin provides a novel interface-engineering design approach for achieving macroscale superlubricity over a broad temperature range, from room temperature to above 200 ℃, and offers an effective strategy for achieving superlubricity on steels. By deliberately engineering a boronized surface that forms in-situ passivating tribofilms during the running-in period, and by pairing it with lubricants rich in hydroxyl groups, researchers unlock robust superlubricity whose upper temperature limit scales directly with the number of –OH groups. MD simulations reveal that at 200 ℃, polyglycerol-10 (with 12 –OH groups) has an oil film thickness 3.6 times greater than that of pure glycerol (with 3 –OH groups), with the hydrogen bond count increasing by 1.6 times. The stronger intermolecular cohesive forces in polyglycerol-10 result in a higher superlubricity failure temperature, which increases from 100 ℃ (for glycerol) to above 200 ℃ (for polyglycerol-10). These interactions help prevent direct asperity contact between friction pairs, maintaining superlubricity even at high temperatures.
This advancement provides theoretical and technical support for the innovative material design and industrial-scale application of high-temperature superlubricity. As macroscale superlubricity continues to develop, this interface-engineered and in-situ friction-induced superlubricity system shows great potential for future applications in aviation mechanical systems, such as aircraft engines and hydraulic pumps.