Friction is a phenomenon observed ubiquitously in daily life, yet its nature is complicated. Friction between rough surfaces is considered to arise primarily because of macroscopic roughness. In contrast, interatomic forces dominate between clean and smooth surfaces. “Superlubricity”, where friction effectively becomes zero, occurs when the ratio of lattice parameters in the pair of surfaces becomes an irrational number. Superlubricity has been found to exist in a limited numb...

The transition from atomic stick-slip to continuous sliding has been observed in a number of ways. If extended contacts are moved in different directions, so-called structural lubricity is observed when the two surface lattices are non-matching. Alternatively, a “superlubric” state of motion can be achieved if the normal force is reduced below a certain threshold, the temperature is increased, or the contact is actuated mechanically. These processes have been partially demonst...

The term “structural lubricity” denotes a fundamental concept where the friction between two atomically ?at surfaces is reduced due to lattice mismatch at the interface. Under favorable circumstances, its effect may cause a contact to experience ultra-low friction, which is why it is also referred to as “superlubricity”. While the basic principle is intriguingly simple, the experimental analysis of structural lubricity has been challenging. One of the main reas...

Superlubricity refers to a sliding regime in which contacting surfaces move over one another without generating much adhesion or friction [1]. From a practical application point of view, this will be the most ideal tribological situation for many moving mechanical systems mainly because friction consumes large amounts of energy and causes greenhouse gas emissions [2]. Superlubric sliding can also improve performance and durability of these systems. In this paper, we attempt to provide an over...

Friction tests have been carried out on bearing steel friction pairs coated with a-C:H and ta-C under lubricated conditions with 1-hexadecene and pure oleic acid, respectively. Main results show that ta-C leads to the super-low regime with oleic acid (friction coefficient below 0.01) and that a-C:H is quite well lubricated by 1-hexadecen. Surface analyses by coupling X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) have been carried out in the case of oleic ac...

In this study, we address the superlubricity behavior of sapphire against ruby (or sapphire against itself) under phosphoric acid solution lubrication. An ultra-low friction coefficient of 0.004 was obtained under a very high contact pressure, with a virgin contact pressure up to 2.57 GPa. Related experiments have indicated that the load, sliding speed, and humidity of the test environment can affect superlubricity to some degree, so we tested variations in these conditions. When superlubrici...

In this work, a super-low friction coefficient of 0.003 was found between a silicon nitride ball and a sapphire plate lubricated by phosphoric acid solution. The wear mainly occurred in the running-in period and disappeared after superlubricity was achieved. The friction coefficient was effectively reduced from 0.3 to 0.003 at a constant speed of 0.076 m/s, accompanied by a 12-nm-thickness film. The lubrication regime was indicated to change from boundary lubrication in the running-in period ...

Superlubricity, or structural lubricity, is a state that has two contacting surfaces exhibiting no resistance to sliding. This effect has been theoretically described to be possible between two completely clean single crystalline solid surfaces. However, experimental observations of superlubricity were limited to nanoscale and under high vacuum or inert gas environments even after twenty years since the concept of superlubricity has been suggested in 1990. In the last two years, remarkable ad...

Tetrahedral amorphous carbon coatings have the potential to significantly reduce friction and wear between sliding components. Here, we provide atomistic insights into the evolution of the sliding interface between naked and hydrogen-passivated ta-C sliding partners under dry and lubricated conditions. Using reactive classical atomistic simulations we show that sliding induces a sp³ to sp² rehybridization and that the shear resistance is reduced by hydrogen-passivation a...