Surface-nitrided layers of Ti–6Al–4V alloy were fabricated using a diode laser in pure and mixed gas atmospheres of nitrogen and argon. The surface morphology, microstructure, hardness, and cracks of the nitrided layers were investigated. In all gas atmospheres, the layers showed smooth and humped regions, and consisted of planar nitrogen titanium (TiN), dendrites, and acicular martensite. The surface roughness was improved dramatically as the nitrogen concentration of the atmosphere was diluted with argon. Overall, the hardness of the nitrided layer was greatest for pure nitrogen and it tended to decrease as the concentration of argon in the atmosphere increased. However, the hardness of the layer for pure nitrogen also decreased rapidly, from the surface to matrix, in comparison to the diluted nitrogen atmospheres. It was shown that the number and size of dendrites, which determine hardness, are controlled by the nitrogen concentration. The dendrites of the nitrided layer were denser and smaller in a pure nitrogen atmosphere, than in diluted nitrogen atmospheres. Longitudinal and transverse cracks were observed in the nitrided layers. These two types of cracks were decreased or even eliminated as the argon concentration of the nitrogen–argon atmosphere was increased. Therefore, by diluting the nitrogen atmosphere with argon, the nitrided layer properties, in terms of surface roughness and cracks, can be improved, but this may also cause a reduction in the layer hardness.

Using pulsed double electrode-gas metal arc welding, aluminum wires are joined to copper plates with fillers of different fractions of silicon. Two layers of different microstructures are formed near the Al-Cu interface: one consists of a hypoeutectic microstructure of α (Al) + Al₂Cu, and the other consists of an intermetallic compound (IMC) of Al₂Cu. Increasing the heat input causes increases in the thicknesses of the IMC layer and the layer of the hypoeutectic microstructure. Si suppresses the growth of the IMC layer and assists the growth of the layer of the hypoeutectic microstructure. The effects of the interface microstructures and chemical compositions on the electric resistivity of the joints are analyzed. The electric resistivity of the joints increases with the increase in the thicknesses of the IMC layer and the layer of the hypoeutectic microstructure. The law of mixture is used to calculate the electric resistivity of the joints, which is in accordance with the experimental results.

Perovskite solar cells (PSCs), since their inception in 2009, have experienced a meteoric rise in power conversion efficiencies (PCEs), challenging established photovoltaic technologies. However, their commercial deployment is hindered by stability and performance issues related to the presence of defects at the perovskite surface and grain boundaries. This study focused on the exploration of Morpholinium tetrafluoroborate (MOT) as a post-treatment additive to mitigate these challenges. Comprehensive characterization techniques revealed that the synergistic action of Morpholine and BF₄⁻ ions in MOT substantially improved the quality of the perovskite films and passivates surface and bulk defects, yielding notable enhancements in device PCE and stability. MOT-doped PSCs exhibited a PCE of 23.83% and retain 92% of the initial PCE after 2000 h of continuous illumination under one sun condition. The findings underscore the significance of additive engineering in advancing perovskite solar cell technology, opening up prospects for high-performing and durable perovskite photovoltaic devices.

The stability of the output speed of a hydraulic system has a great influence on the working performance of hydraulic equipment. It changes with the system working conditions. The increase in leakage caused by the wear of the hydraulic kinematic pair and the slip of the motor lead to the instability of the output speed. Although the hydraulic system can satisfy the output requirements of the active control scheme with ex ante decision making or the passive feedback control strategy with ex post compensation, it also causes an increase in system complexity and manufacturing cost. The speed stiffness as a basic characteristic of the output of the hydraulic system has not been sufficiently investigated and evaluated. In this paper, the IFMDH (inverter-fed, motor-driven hydraulic) system is taken as the object, and the coupling relationship of each link of the system is revealed by mathematical modelling. The reliability of the model is verified under a wide range of speed and load variations in combination with experiments. By redefining the speed stiffness quantification method, the effects of load conditions, motor stiffness, and speed ratio at the output end on the speed stability of the system are discussed in conjunction with the system coupling mechanism model. The conclusions show that the motor stiffness and the addition of a speed reducer have a significant effect on the system speed stiffness, where changing the output speed ratio has a significant effect on the speed stiffness. The conclusions of the study provide technical support for the rapid design, selection, and system optimisation of hydraulic systems in common scenarios.

The laser gas oxidising of Ti–6Al–4V surface was studied. Confocal laser scanning microscopy techniques were used to investigate its two- and three-dimensional surface topographies. Gas flow behaviour was simulated to define the minimum O₂ concentration required for Ti–6Al–4V to self-sustain combustion. To understand the flow behaviour of the Ti–6Al–4V fluid, a high-speed camera monitored the evolution of the Ti–6Al–4V fluid, and the flow behaviour was simulated. Experimental and simulation results show that Ti–6Al–4V can self-sustain combustion with a high O₂ to Ar gas flow ratio, and the oxidising layer is rough with macroscopic cracks, while a low O₂ to Ar gas flow ratio results in a smooth oxidising layer without cracks. Ti–6Al–4V can self-sustain combustion when the O₂ concentration exceeds 65%. Furthermore, the laser molten pool and self-sustaining combustion zone mix and flow together, and a large self-sustaining combustion zone leads to a low convection velocity.

Real-time measuring and obtaining surface tension of liquid metal during the arc welding process is critical for studying the behavior of the weld pool, such as Marangoni flow and flow velocity. The dynamic variation of surface tension of weld pool during tungsten inert gas welding process with and without fluoride flux was measured by weld pool oscillation sensing system, and the effect of fluoride flux on surface tension and pool behavior was analyzed. The results show that the surface tension gradient of liquid metal can convert from a negative to a positive value in a critical arc time. The flow velocity of liquid metal and critical arc time significantly increased and decreased, respectively, with fluoride flux. The variation of surface tension, flow velocity, and critical arc time with fluoride flux was induced by arc temperature increasing.