Friction and wear usually lead to huge energy loss and failure of machine pairs, which usually causes great economic losses. Researchers have made great efforts to reduce energy dissipation and enhance durability through advanced lubrication technologies. Single-layer coatings have been applied in many sectors of engineering, but the performance of single-layer coatings still has many limitations. One solution to overcome these limitations is to use a multilayer coating that combines different components with varied physical and chemical properties. In addition, multilayer coating with alternating layers only containing two components can lead to improved performance compared to a coating with only two different layers. This paper systematically reviews the design concept and properties of different types of multilayer coatings, including transition-metal nitride coatings, diamond-like carbon-based coatings, and other multilayer coatings. The inherent functional mechanisms of the multilayer structures are also detailed and discussed.

Biomachine hybrid robots have been proposed for important scenarios, such as wilderness rescue, ecological monitoring, and hazardous area surveying. The energy supply unit used to power the control backpack carried by these robots determines their future development and practical application. Current energy supply devices for control backpacks are mainly chemical batteries. To achieve self-powered devices, researchers have developed solar energy, bioenergy, biothermal energy, and biovibration energy harvesters. This review provides an overview of research in the development of chemical batteries and self-powered devices for biomachine hybrid robots. Various batteries for different biocarriers and the entry points for the design of self-powered devices are outlined in detail. Finally, an overview of the future challenges and possible directions for the development of energy supply devices used to biomachine hybrid robots is provided.

It has been recognized that purposefully designed surface texturing can contribute to the improvement of tribological performance of elements and friction reduction. However, its optimal parameters may depend on the operating conditions. This paper investigated the effect of a triangle-shaped dimples array on the tribological performance of the lubricated point-contacts under different lubrication regimes, based on the rotational sliding experiment of a patterned steel disk against smooth steel balls. The dimples arrays were produced by laser process and characterized by the 3D profilometer. A series of tests were conducted with different dimple parameters including depth, coverage ratio, size, and direction. Stribecklike curves were obtained to depict the transition of lubrication regimes, and the electrical contact resistance was utilized to qualitatively characterize the lubrication status. The test results showed that the dimples arrays with different sizes, depths and coverage ratios had a distinct effect on the friction behaviors. Compared with the nontextured surfaces, when the dimple depth decreased from 30μm to zero with fixed coverage ratio and size, the friction coefficient firstly decreased, and then increased. The friction coefficient finally approached that of the nontextured surface, during which the lowest value appeared at the dimple depth of approximately 10∼15μm. The coverage ratio of texture showed the similar effect on the friction coefficient. Usually, the coverage ratio of approximately 10% resulted in the lowest friction coefficient. The dimple size and direction also had obvious effects on the friction coefficient. Thus, it can be concluded that there exists a set of optimal values for the dimple depth, coverage ratio, size, and direction to realize the friction reduction.