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Molecular orientation of the lubricating film will affect the lubrication state, especially in boundary lubrication. In this work, electrical field was used to affect the orientation of liquid crystal molecules during friction. We demonstrated that the use of an electric field applied between the steel ball and the chromium film on the surface of the glass plate provided an effective method for controlling the orientation of the liquid crystal molecules in a sliding point contact. The coupling effects of shear and electric field on friction were investigated with an in situ Raman spectrometer. This work shed new light on the influence of the adsorbed film on sliding friction coefficient, especially in thin-film lubrication regime. [ABSTRACT FROM AUTHOR]

• Images of vapor plume in high-speed laser welding are captured through high-speed imaging. • Influences of laser power and welding speed on the behavior of vapor plume are analyzed. • Humping occurrence are predicted with the random forest and a sliding time window. The increase of welding speed can improve the productivity of laser welding. The behavior of vapor plume is an important indicator reflecting the state of the laser welding process. However, the behavior of vapor plume in high-speed laser welding (whose welding speed is higher than 10 m/min) has not been studied adequately. In this research, images of the vapor plume in high-speed laser welding of SUS304 austenitic stainless steel are captured through high-speed imaging for the monitoring of the welding process. Characteristics of the vapor plume are extracted with image processing, and the influences of laser power and welding speed on these characteristics are analyzed. The relationships between the behavior of vapor plume and melt pool are discussed, and three ejection regimes of the vapor plume are proposed. In order to predict the occurrence of humping, which is a typical defect in high-speed laser welding, samples are built by applying a time sliding window and then a classification model is built with the random forest. In addition, the importance of features in the classification is analyzed. The test results show that the proposed method can predict the humping defect in high-speed laser welding accurately. [ABSTRACT FROM AUTHOR]

• The mechanism of action of thermal bubbles at the solid–liquid interface was studied for the first time. • Unveiling the underlying mechanisms of liquid metal droplet ejection. • The potential of utilizing this technology to achieve multi-orifice liquid metal jetting was demonstrated. In this work, we introduced the pulsed laser-driven liquid metal arrayed printing technology. This study harnesses sub-millimeter-sized rapidly expanding bubbles generated by nanosecond pulsed laser irradiation at the solid–liquid interface as the power source for liquid metal printing, enabling efficient arrayed jetting printing of liquid metal. Utilizing high-speed imaging technology, this study investigates the expansion process of bubbles induced by nanosecond pulsed lasers at the solid–liquid interface and the jetting process of liquid metal, thereby revealing the mechanism of liquid metal jet ejection. The study systematically examines the influence of laser parameters on the jetting behavior of liquid metal, laying a theoretical and technical foundation for applications such as patterned printing in the field of liquid metal. This technology holds significant engineering implications for further advancing the application of liquid metal in fields such as flexible electronics and printed electronics. [ABSTRACT FROM AUTHOR]

• Inconel 617 Ni-based superalloy sheets were joined using a laser-welding process under four different welding positions. • When using high-heat input parameters, the welding position has an obvious effect on the laser weld's quality. • Different welding positions generated different levels of hydrostatic melt pressure on the keyhole surface. Inconel 617 Ni-based superalloy sheets were joined using a laser-welding process. The welding experiments were conducted on four different welding positions (i.e., flat, horizontal, vertical-up, and vertical-down), using two sets of welding parameters with different heat inputs. Then, the geometry, internal defects, mechanical properties, and molten-pool dynamics of the laser joints were evaluated. The results showed that, when using high-heat input parameters, the welding position has an obvious effect on the laser weld quality. The top surface of the flat weld and the root surface of the vertical-down weld are both slightly concave. Moreover, the horizontal weld and vertical-down weld have serious keyhole-induced porosity defects, which lead to relatively worse mechanical properties. The analysis shows that the stability of keyhole differs for different welding positions; keyhole-induced porosity is easily generated in the horizontal and vertical-down positions. Moreover, solid metal blocks escape routes of the bubbles, resulting in more serious porosity for these welding positions. However, when using low-heat input parameters, the welding position has less influence on the laser weld quality because there is less molten metal, which makes the keyhole more stable in different welding positions. [ABSTRACT FROM AUTHOR]