Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material’s surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis. To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. A well-known example is the use of photocatalytic TiO2 nanoparticle coatings that become superhydrophilic under UV irradiation. Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. The key to these two “wet”-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently “wet” nature. Thus, a “dry”-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves and the striking ability of a water-strider’s legs to walk on water can be attributed to the ideal superhydrophobicity of their surfaces, induced by special microand nanostructures. To date, the biomimetic fabrication of superhydrophobic microand/or nanostructures has attracted considerable interest, and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale—so small that they can be easily trapped in the interspaces among micropapillae. Thus, lotuslike surface microstructures are unsuitable for superhydrophobic antifogging coatings, and a new inspiration from nature is desired for solving this problem. In this communication, we report a novel, biological, superhydrophobic antifogging strategy. It was found that the compound eyes of the mosquito C. pipiens possess ideal superhydrophobic properties that provide an effective protective mechanism for maintaining clear vision in a humid habitat. Our research indicates that this unique property is attributed to the smart design of elaborate microand nanostructures: hexagonally non-close-packed (ncp) nipples at the nanoscale prevent microscale fog drops from condensing on the ommatidia surface, and hexagonally close-packed (hcp) ommatidia at the microscale could efficiently prevent fog drops from being trapped in the voids between the ommatidia. We also fabricated artificial compound eyes by using soft lithography and investigated the effects of microand nanostructures on the surface hydrophobicity. These findings could be used to develop novel superhydrophobic antifogging coatings in the near future. It is known that mosquitoes possess excellent vision, which they exploit to locate various resources such as mates, hosts, and resting sites in a watery and dim habitat. To better understand such remarkable abilities, we first investigated the interaction between moisture and the eye surface. An ultrasonic humidifier was used to regulate the relative humidity of the atmosphere and mimic a mist composed of numerous tiny water droplets with diameters less than 10 lm. As the fog was C O M M U N IC A IO N

The dry-style antifogging properties of mosquito compound eyes and artificial analogues prepared by soft lithography: a superhydrophobic state with high adhesive force

The surface integrity of machined metal components is critical to their in-service functionality, longevity and overall performance. Surface defects induced by machining operations vary from the nano to macro scale, which cause microstructural, mechanical and chemical effects. Hence, they require advanced evaluation and post processing techniques. While surface integrity varies significantly across the range of machining processes, this paper explores the state-of-the-art of surface integrity research with an emphasis on their governing mechanisms and emerging evaluation approaches. In this review, removal mechanisms are grouped by their primary energy transfer mechanisms; mechanical, thermal and chemical based. Accordingly, the resultant multi-scale phenomena associated with metal machining are analyzed. The contribution of these material removal mechanisms to the workpiece surfaces/subsurface characteristics is reviewed. Post-processing options for the mitigation of induced surface defects are also discussed.

Surface integrity in metal machining - Part I: Fundamentals of surface characteristics and formation mechanisms

UV laser high-quality drilling of CFRP plate with a new interlaced scanning mode

Film cooling holes (FCHs) of nickel-based single crystal turbine blades were drilled by 532 nm Nd:YVO4 nanosecond laser in coaxial waterjet-assisted environment. Microstructure of the side wall of the FCHs was mainly investigated by means of transmission electron microscopy. The average thickness of heat affected zone (HAZ) around FCHs decreases with increasing of water flow rate. The main phase within HAZ evolves from β-NiAl to β-NiAl + γ-Ni with the increase in the water flow rate. Some γ-Ni particles in the HAZ twined along (111) plane. A small portion of the FCHs are free of HAZ when drilled by coaxial waterjet-assisted laser drilling at a laminar water flow rate ≥3.1 m/s. There are no processing-induced defects including HAZ, microcrack, and phase transformation around the FCHs when drilled at the water flow rate ≥5.1 m/s. The FCHs with high surface quality can be drilled by the coaxial waterjet-assisted laser drilling. Finally, effects of fluid water on drilling quality of the FCHs were discussed.

Coaxial waterjet-assisted laser drilling of film cooling holes in turbine blades

Dual-beam laser drilling process for thick carbon fiber reinforced plastic composites plates

Study on immersion waterjet assisted laser micromachining process

Effects of incidence angle and optimization in femtosecond laser polishing of C/SiC composites

In traditional air laser processing of CFRP (cutting), defects such as excessive heat-affected zone(HAZ), fiber extraction, material delamination, and fiber end expansion could occur near the incision. We proposed nanosecond water-assisted laser processing technology and conducted CFRP process research.CFRP has the characteristics of high specific strength, high specific rigidity, light weight and anisotropy. These characteristics make the machining of high-quality CFRP cuts very demanding on parameters, but traditional machining methods always make CFRP defects. The test sample was a CFRP sheet with a thickness of 3mm, which required smooth and even incisions. The test method was to conduct comparative experiments of nanosecond laser grooving in the air and water respectively to test the manufacturing efficiency, the surface roughness of the incision, and the HAZ of inner wall, we also discussed the formation mechanism of notch defects. In comparative experiments, it was found that the quality of the incision was related to the heat accumulation/dissipation ratio. This was related to the single pulse energy, pulse width, and thermal conductivity of the material. In the cut area of CFRP processed in the air, there were phenomena such as thick HAZ, scattered fibers, and slagging. The convective heat transfer of water removes a lot of heat, which significantly reduced the accumulated heat. In general, the water-assisted laser processing could make better cuts. However, it is found that there were some pits near the surface of incisions, which may be caused by the cavitation of tiny bubbles. The shock wave generated by the bubble explosion would not only destroy the fiber structure and increase the residual stress, making the radiation energy distribution uneven, but also brought damages to surrounding materials. We conduct single factor variable experiment at different single pulse energy, overlap rate, and water flow velocity. It is found that under the same frequency, overlap rate and water flow speed, as the energy of a single pulse increased, the HAZ of the material became larger. At a fixed frequency, single pulse energy and water flow velocity, as the moving speed of plate increased, the ablation threshold of the material also increased. It is speculated that it was caused by the scattering effect of small bubbles. The bubbles in the previous pulse could affect the ablation of the next pulse. In the case of small single pulse energy, low overlap rate and high water flow velocity, the influence of bubbles was weakened, and the bubbles in the previous pulse hardly affected the next pulse. Under the conditions of large pulse energy and high overlap rate, there were many large-sized bubbles and the quality of the cut was poor. Under large single pulse energy, high moving speed and high water speed, the cutting quality was the highest and the processing efficiency was high.

Research on water-assisted laser processing of CFRP

The problems of the recast layer, oxide layer, and heat-affected zone (HAZ) in conventional laser machining seriously impact material properties. Coaxial waterjet-assisted laser scanning machining (CWALSM) can reduce the conduction and accumulation of heat in laser machining by the high specific heat capacity of water and can realize the machining of nickel-based special alloy with almost no thermal damage. With the developed experimental setup, the laser ablation threshold and drilling experiments of the K4002 nickel-based special alloy were carried out. The effects of various factors on the thermal damage thickness were studied with an orthogonal experiment. Experimental results have indicated that the ablation threshold of K4002 nickel-based special alloy by a single pulse is 4.15 J/cm2. The orthogonal experiment results have shown that the effects of each factor on the thermal damage thickness are in the order of laser pulse frequency, waterjet speed, pulse overlap rate, laser pulse energy, and focal plane position. When the laser pulse energy is 0.21 mJ, the laser pulse frequency is 1 kHz, the pulse overlap is 55%, the focal plane position is 1 mm, and the waterjet speed is 6.98 m/s, no thermal damage machining can be achieved. In addition, a comparative experiment with laser drilling in the air was carried out under the same conditions. The results have shown that compared with laser machining in the air, the thermal damage thickness of CWALSM is smaller than 1 μm, and the hole taper is reduced by 106%. There is no accumulation and burr around the hole entrance, and the thermal damage thickness range is 0–0.996 μm. Furthermore, the thermal damage thickness range of laser machining in the air is 0.499–2.394 μm. It has also been found that the thermal damage thickness is greatest at the entrance to the hole, decreasing as the distance from the entrance increases.

https://www.mdpi.com/2072-666X/14/3/641/pdf?version=1678615596

Experimental Study on Coaxial Waterjet-Assisted Laser Scanning Machining of Nickel-Based Special Alloy

Air-film cooling holes were drilled into a turbine blade with a 532-nm Nd:YVO4 nanosecond laser in air and with coaxial waterjet assistance. The drilling quality of the sidewalls of the holes was investigated comparatively by means of a 3D confocal laser scanning microscope, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy. Results have shown that the maximum thickness of the processing-induced defects around the air-film cooling holes drilled by the laser in air is up to 100 µm, while the holes obtained by means of the asynchronous operation of laser drilling in air and coaxial waterjet assistance indicate no spatter, oxide layer, recast layer or cracks. Compared with laser drilling in air, the minimum size of the heat-affected zone around the air-film cooling holes induced by asynchronous processing is decreased down to the sub-micrometer scale. The main phases in the oxide layer, recast layer and heat-affected zone are α-Al2O3, γ-Ni, and β-NiAl, respectively. Asynchronous processing can help us achieve high position precision and it will have wide application. 
are α-Al2O3, γ-Ni, and β-NiAl, resp

/pdf/laser-drilling-of-air-film-cooling-holes-in-air-and-with-2pwixi30.pdf

Laser drilling of air-film cooling holes in air and with coaxial waterjet assistance

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