Solid superlubricity of diamond-like carbon films: a review

Abstract With the origin of life and the advancement of human society, friction has become an integral part of human civilization’s development. Approximately one-third to one-half of the world’s energy consumption is attributed to friction. Lubrication plays a crucial role in reducing friction and wear, enhancing resource efficiency, and promoting a green industry. Achieving superlubricity, where friction approaches zero, is one of the primary research objectives in lubrication science. The evolution of superlubricity has progressed from theoretical to experimental validation, transitioning from atomic-scale superlubricity on perfect crystal planes to various macro-scale applications today. Unlike two-dimensional materials, diamond-like carbon (DLC) films can be deposited onto metal substrates and exhibit high hardness (10–80 GPa), enabling better resistance to local deformation and wear, and reducing material loss. This allows DLC films to maintain performance under high loads. Together with the elastic modulus, hardness determines the deformation behavior of DLC films under load. DLC films with high hardness typically have a high elastic modulus, making them less prone to plastic deformation under normal load and enhancing their load-bearing capacity. These characteristics make DLC films one of the most promising candidates for engineering superlubricity applications. By carefully choosing suitable testing environments, element doping methods, or subjecting carbon films to hydrogen plasma treatment, superlubricity has been successfully achieved across various conditions. This paper comprehensively sums up the current understanding of superlubricity of DLC films. The discussion follows a logical sequence: starting with the superlubricity of hydrogenated DLC films, then moving on to element-doped DLC films, followed by special structure DLC films, and finally exploring the synergy superlubricity of DLC films. The paper concludes with an in-depth analysis of the industrial prospects of macro-scale superlubricity for DLC films.