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With the increasing demand for drag reduction, energy consumption reduction, and low weight in civil aircraft, high-precision microgroove preparation technology is being developed internationally to reduce wall friction resistance and save energy. Compared to mechanical processing, chemical etching, roll forming, and ultrafast laser processing, nanosecond lasers offer processing precision, high efficiency, and controllable thermal effects, enabling low-cost and high-quality preparation of microgrooves. However, the impact of nanosecond laser etching on the fatigue performance of substrate materials remains unclear, leading to controversy over whether high-precision shape control and fatigue performance enhancement in microgrooves can be achieved simultaneously. This has become a bottleneck issue that urgently needs to be addressed. This paper focuses on the current research status of nanosecond laser processing quality control for microgrooves and the research status of laser effects on enhancing the fatigue performance of substrate materials. It identifies the main existing issues: (1) how to induce surface residual compressive stress through the thermo-mechanical coupling effect of nanosecond lasers to suppress micro-defects while ensuring high-precision shape control of fixed microgrooves; and (2) how to quantify the regulation of nanosecond laser process parameters on residual stress distribution and fatigue performance in the microgroove area. To address these issues, this paper proposes a collaborative strategy for high-quality shape control and surface strengthening in fixed microgrooves, an analysis of multi-dimensional fatigue regulation mechanisms, and a new method for multi-objective process optimization. The aim is to control the geometric accuracy error of the prepared surface microgrooves within 5% and to enhance the fatigue life of the substrate by more than 20%, breaking through the technical bottleneck of separating “drag reduction design” from “fatigue resistance manufacturing”, and providing theoretical support for the integrated manufacturing of “drag reduction-fatigue resistance” in aircraft skins.

Superhydrophobic surfaces can effectively enhance the corrosion resistance of magnesium alloys. This paper proposes a new method for preparing superhydrophobic surfaces based on the combination of laser processing and chemical-assisted thermal decomposition of stearic acid using pulse laser chemistry. Nanosecond pulse laser is used to etch the surface of 1.5 mm AZ31B magnesium alloy, and the influence of different laser power, etching spacing, and frequency on the superhydrophobic surface properties of AZ31B magnesium alloy is investigated by adjusting the parameters. Different surface micro-nano structures are manufactured by changing the pulse laser movement trajectory, and the influence of different surface micro-nano structures on the superhydrophobic properties of AZ31B magnesium alloy is explored. This paper analyzed the effects of micro-nano structures on the surface of AZ31B magnesium alloy using techniques such as electron microscopy and energy dispersive spectrometer. The corrosion resistance of magnesium alloy specimens treated by laser chemical processing is significantly improved. Graphical abstract

Laser surface texturing (LST) is a non‐contact manufacturing process for fabricating functional surfaces in a manner that improves the corresponding wettability, and is widely used in biomedicine and industry. Laser surface texturing is a facile approach that is compatible with various materials, can result in a hierarchical texture, and enables a high degree of surface wetting (i.e., extreme wetting). In addition to surface structures, surface chemical modification is a primary factor in producing extreme wetting surfaces. This review discusses the effects of various surface textures and surface chemistries on wettability. Optimal laser parameters for the desired surface texture are based on the fundamental wettability and laser mechanism. In particular, bumps in the morphology are conducive to obtaining extreme wetting. Diverse surface chemical strategies result in extreme wetting by different mechanisms. This paper makes a rigorous evaluation of the laser parameters and optimal surface chemical modifications by elucidating the relationships between the surface structure, surface chemical modification, and wettability, and in so doing, determines the final wettability. The unresolved problems of LST are presented in the conclusion. This review provides guidance, development directions, and an integrated framework for LST, which will be useful for fabricating extreme wetting surfaces on various metals.

Nanosecond laser ablated metallic surfaces showed initial super-hydrophilicity, and then experienced gradual wettability conversion to super-hydrophobicity with the increase of exposing time to ambient air. Due to the presence of hierarchical structures and change of surface chemistry, the laser-induced Inconel alloy surfaces showed a stable apparent contact angle beyond 150° over 30-day air exposure. The wetting states were proposed to elucidate the initial super-hydrophilicity and the final super-hydrophobicity. The basic fundaments behind the wettability conversion was explored by analyzing surface chemistry using X-ray photoelectron spectroscopy (XPS). The results indicated that the origins of super-hydrophobicity were identified as the increase of carbon content and the dominance of C–C(H) functional group. The C–C(H) bond with excellent nonpolarity derived from the chemisorbed airborne hydrocarbons, which resulted in dramatic reduction of surface-free-energy. This study confirmed that the surface chemistry is not the only factor to determine surface super-hydrophobicity. The laser-induced super-hydrophobicity was attributed to the synergistic effect of surface topography and surface chemical compositions. In this work, the corresponding chemical reaction was particularly described to discuss how the airborne hydrocarbons were attached onto the laser ablated surfaces, which reveals the generation mechanism of air-exposed super-hydrophobic surfaces.

Capillary-gradient wicks can achieve fast or directional liquid transport, but they face fabrication challenges by traditional methods in terms of precise patterns. Laser processing is a potential solution due to its high pattern accuracy, but there are a few studies on laser-processed capillary-gradient wicks. In this paper, capillary step-gradient micro-grooved wicks (CSMWs) were fabricated by an ultraviolet nanosecond pulsed laser, and their capillary performance was studied experimentally. The CSMWs could be divided into three regions with a decreasing capillary radius. The equilibrium rising height of the CSMWs was enhanced by 124% compared to the non-gradient parallel wick. Different from the classical Lucas–Washburn model describing a uniform non-gradient wick, secondary capillary acceleration was observed in the negative gradient direction of the CSMWs. With the increase in laser power and the decrease in scanning speed, the capillary performance was promoted, and the optimal laser processing parameters were 4 W-10 mm/s. The laser-enhanced capillary performance was attributed to the improved hydrophilicity and reduced capillary radius, which resulted from the increased surface roughness, protrusion morphology, and deep-narrow V-shaped grooves induced by the high energy density of the laser. Our study demonstrates that ultraviolet pulsed laser processing is a highly efficient and low-cost method for fabricating high-performance capillary gradient wicks.

The super-hydrophobic copper surface was obtained by using a nanosecond pulsed laser. Different micro- and nano-structures were fabricated by changing the laser scanning interval and scanning speed, before heating in an electric heater at 150 °C for two hours to explore the effect of laser parameters and heat treatment on the wettability of the copper surface. It was found that the laser-treated copper surface is super-hydrophilic, and then, after the heat treatment, the surface switches to hydrophobic or even super-hydrophobic. The best super-hydrophobic surface’s apparent contact angle (APCA) was 155.6°, and the water sliding angle (WSA) was 4°. Super-hydrophobic copper is corrosion-resistant, self-cleaning, and dust-proof, and can be widely used in various mechanical devices.

Due to the introduction of silicon carbide reinforcement, the physical and cutting properties of SiCp/Mg composites are very different from those of metal composites. Nanosecond pulse laser processing is more efficient than traditional processing for SiCp/Mg composites. A low-power pulsed fiber laser was used to etch 3.0 mm thick SiCp/Mg composites. The effect of low laser power (0~50 W) on the morphology and heat-affected zone of the SiCp/Mg composite after etching was studied. The results show that when the laser power increases, the material accumulation at the ablation end of the machining surface becomes more and more serious. With the increase in power, the differences in ablation width and ablation depth on the surface of composite materials do not increase proportionally. When the laser power increases gradually, the width of the heat-affected zone increases in the direction of the perpendicular laser beam and reaches the maximum value at the etched end.

The additive manufacturing is a free-form metal deposition process, which allows generating a prototype or small series of near net-shape structures. Despite numerous advantages, one of the most critical issues of the technique is that produced pieces have a deleterious surface quality which requires post machining. Besides conventional post processes such as turning, milling, or photo-chemical etching, laser processes are increasingly being used for surface finishing of metals. In this study, a hybrid laser polishing technique consisting of nanosecond pulsed laser material removal and continuous wave (CW) laser polishing was utilized to polish the laser directed energy deposition (LDED) Ti-6Al-4 V samples. To account for this, the effect of hybrid laser polishing on the surface modification of LDED Ti-6Al-4 V alloy has been investigated. The surface morphology, microstructure evolution, and mechanical properties of the as-fabricated, the pulsed laser material removal processed, and the hybrid laser polishing processed samples were investigated. The results revealed that hybrid laser polishing not only eliminates the unmelted particles, oxides, and defects of as-fabricated Ti-6Al-4 V but also reconstructs the surface morphology, which improved the surface roughness by 98.32%. After hybrid laser polishing, the average thickness of the remelted layer has increased to 85 μm, while the acicular martensite α´ grows epitaxially from the substrate across the layer bands. Additionally, due to the formation of α′ martensite, the microhardness is about 21.02% higher than LDED Ti-6Al-4 V sample. The wear rate is decreased from 1.36 × 10−3 to 0.86 × 10−3 mm3/N·m, which was reduced by 38.23% compared to the as-fabricated.

For the first time, a detailed comprehensive study is conducted of the dry etching of dislocation and dislocation-free samples of germanium on planes {111}, {110}, and {100}. Etching is performed by exposure to pulses of nanosecond ultraviolet (UV) laser radiation of the subthreshold intensity (wavelength, 355 nm; duration, ~10 ns; energy density, ~0 . 5–1 . 3 J/cm 2 ; pulse repetition rate, 100 Hz; and divergence, 1–2 mrad). Before and after the laser heat treatment of the surface, the samples are examined using a Zygo optical profilometer and a scanning electron microscope. Features of the nature of the damage to the surfaces corresponding to different crystallographic planes of single crystals of industrial dislocation germanium are revealed. They are compared with the data on the subthreshold damage of typical dislocation-free crystals. It is shown that in dislocation samples of germanium on the {111} plane, it is possible to create a regime of exposure to radiation, leading to the formation of etch pits, which is outwardly identical to the dislocation pits detected during selective chemical etching. Their concentration corresponds in order of magnitude to the density of dislocations. On the {100} plane of dislocation samples, etching results are also found, which clearly have a crystallographic nature. At the energy density of the acting radiation ≥0.4 J/cm 2 on the surfaces of dislocation (plane {100}) and dislocation-free germanium (planes {111}, {100}, {110}), only individual spots of ~50 µm and individual microcraters of ~0.1–1 µm having crystallographic features are recorded. The possibility of the environmentally friendly detection of dislocations in germanium without the use of chemical reagents is shown.

Aluminum alloy 2024 is the most widely used metal alloy in aircraft due to its superior characteristics. Although the effects of surface chemistry and topography on the wettability transition have been investigated in the literature, it has not yet been clarified which mechanism is more dominant. In this study, the super-hydrophobic Al2024 sample surfaces were obtained over time in a single step using a nanosecond pulsed fiber laser. Different micro- and nano-structures were produced by changing the laser output power and scanning speed. The effects of laser parameters on the wettability of the Al2024 samples were examined. As with the untreated sample, all fresh laser-treated samples have a hydrophilic or super-hydrophilic surface property. It was found that the fresh laser-treated aluminum alloy surfaces were super-hydrophilic. Then, the Al2024 samples were exposed to ambient air for a certain period. It was found that the contact angles (CAs) of all laser-treated Al2024 samples increased over time. Also, the water drop moved away from the surface of some super-hydrophobic samples at angles of less than 10°. With more than 150° water contact angle and less than 10° sliding angle, it was proved that the lotus effect was obtained at various time scales. The icing properties of the lotus sample were investigated. The surface icing characteristics of the lotus sample have been improved. The XPS high resolution analyses show that the Al-C bond could be responsible for the wettability transition of the laser-ablated samples from hydrophilic to super-hydrophobicity (lotus). Graphical Abstract