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ABSTRACT Alumina tiles are textured by a laser beam to obtain improved hydrophobic characteristics at the surfaces. Since the textured surfaces are optically opaque, the resulting surfaces are copied and replicated by polydimethylsiloxane (PDMS). Some of the texture features such as whiskers-like structures with complex shapes could not be copied by PDMS and synthesized silica particles are deposited onto PDMS copied and replicated surfaces to create a lotus effect. Analytical tools are incorporated to characterize the PDMS copied and replicated surfaces as well as synthesized silica particles deposited surfaces. Dynamic water contact angle measurements are carried out to assess hydrophobic characteristics of the resulting surfaces. It is found that PDMS copied and replicated surfaces have almost identical surface texture morphology to that of laser treated surface. Introducing synthesized silica particles improved the lotus effect on the PDMS copied and replicated surfaces; in which case, the hysteresis of droplet contact angle remains significantly low. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44015. [ABSTRACT FROM AUTHOR]

Laser surface melting of hot pressed aluminum composite tile, consisting of 90 % aluminum and 10 % WC, is carried out. Temperature and stress fields developed in the laser-treated region are modeled and predicted using ABAQUS finite element code in line with the experimental conditions. The spiral motion of the laser beam is incorporated at the surface during the laser scanning. This arrangement provides self-annealing effect on the initially formed laser scanning tracks through heat conduction from the lately formed laser scanning tracks. Surface temperature predictions are validated through the thermocouple data. Morphological and metallurgical changes in the laser-treated layer are examined using optical and electron scanning microscopes. It is found that the cooling rates in the central region of the workpiece remain low because of the self-annealing effect of the lately formed laser scanning tracks. This, in turn, lowers von Mises stress levels in this region. Stress peaks are formed below the surface because of the high thermal strain formed in this region during the cooling cycle. The spiral scanning of the laser beam causes oscillating stress levels in the surface region of the laser-treated layer; in which case, its amplitude reduces with the progressing time. Laser-treated layer is free from cracks and crack networks, which is associated with the self-annealing effect of the lately formed laser scanning tracks. [ABSTRACT FROM AUTHOR]

Abstract: Laser gas assisted controlled melting of alumina tile surface is carried out in this work. A carbon coating containing 5% of B4C particles is formed at the tile surface prior to laser treatment process. The morphological and microstructural changes in the treated layer are examined using X-ray diffraction, energy dispersive spectroscopy, and scanning electron microscope. The surface microhardness is measured and the residual stress formed at the surface vicinity is obtained from the X-ray diffractograms. It was found that microhardness of the surface increases significantly after the laser treatment process, which is attributed to high cooling rates and the formation of nitride species at the surface. The residual stress formed at the surface is compressive and no micro- or major-cracks are observed at the laser treated surface. [Copyright &y& Elsevier]

Abstract: Laser pulse heating of metallic surfaces results in rapid rise of temperature in the region irradiated by the laser beam. This in turn results in high temperature gradient in this region. The irradiated substrate material expands as a response to the temperature gradient. Consequently, high thermal stress levels are developed in the region of the high temperature gradient. In the present study, closed form solutions for temperature and stress fields due to a laser pulse decaying exponentially in time are presented. A Laplace transformation method is employed in the analysis. The resulting equations are non-dimensionalized with the appropriate parameters. It is found that temperature rises rapidly during the early heating period in the surface region. In this case, internal energy gain dominates the conduction losses from the surface vicinity. The thermal stress levels attain high values in the surface region. The stress wave developed is compressive and it propagates with a wave speed c 1 inside the substrate. [Copyright &y& Elsevier]

Laser treatment of alumina surfaces is carried out under high pressure nitrogen assisting gas ambient to generate a selective surface in relation to solar heating applications. Laser treated surfaces are sol–gel coated for protection from the dust settlements and the mud formation in the humid air environments. Morphological and metallurgical changes in the laser treated layer are examined using analytical tools incorporating scanning electron microscope (SEM), atomic force microscope (AFM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The optical characteristics of the sol–gel coating are assessed by incorporating ellipsometer. The residual stress formed in the laser treated layer is determined from X-ray (XRD) and Fourier transform infrared spectroscopy (FTIR) data. The influence of the mud, formed from the dust particles, on the surface characteristics of laser treated, and laser treated and sol–gel coated surfaces are examined and the adhesion work required to remove the dry mud from the surfaces are determined from the tangential force data obtained from micro-tribometer. The findings revealed that the laser treated and sol–gel coated alumina surfaces provide superior surface characteristics in the harsh environments because of weak adhesion between the mud formed from the dust particles and the coating surface. This is associated with the small texture height of the sol–gel coating, which lowers the area of the interfacial contact between the mud and the coated surface, and relatively lower surface energy of the sol–gel coating as compared to that of the laser treated surface. The sol–gel coating does not alter the optical characteristics of the laser treated surface. [ABSTRACT FROM AUTHOR]

Laser gas assisted texturing of alumina surface is carried out, and formation of nitride and oxynitride compounds in the surface vicinity is examined. The laser parameters are selected to create the surface topology consisting of micro/nano pillars with minimum defect sites including micro-cracks, voids and large size cavities. Morphological and hydrophobic characteristics of the textured surface are examined using the analytical tools. The characteristics of the environmental dust and its influence on the laser textured surface are studied while mimicking the local humid air ambient. Adhesion of the dry mud on the laser textured surface is assessed through the measurement of the tangential force, which is required to remove the dry mud from the surface. It is found that laser texturing gives rise to micro/nano pillars topology and the formation of AlN and AlON compounds in the surface vicinity. This, in turn, lowers the free energy of the textured surface and enhances the hydrophobicity of the surface. The liquid solution resulted from the dissolution of alkaline and alkaline earth metals of the dust particles in water condensate forms locally scattered liquid islands at the interface of mud and textured surface. The dried liquid solution at the interface increases the dry mud adhesion on the textured surface. Some dry mud residues remain on the textured surface after the dry mud is removed by a pressurized desalinated water jet. [ABSTRACT FROM AUTHOR]

Laser treatment of hot pressed mixture of aluminum (85 wt%) and B 4 C (15 wt%) is carried out. Metallurgical and morphological changes at the laser treated surface are examined using the analytical tools. Microhardness and fracture toughness of the workpiece surfaces are determined prior to and after the laser treatment process. Texture and hydrophobicity of the laser treated surface is assessed incorporating the atomic force microscopy and contact angle measurements. It is found that a dense layer consisting of fine grains of sub-micron sizes (0.8–0.4 μm) and B 4 C particles is formed at the laser treated surface. Microhardness increases at the laser treated surface because of the presence of the dense layer and the formation of AlN compounds at the surface. Fracture toughness of the laser treated surface reduces slightly because of the microhardness enhancement at the surface. The textures of the laser treated surface compose of micro/nano poles, which result in higher contact angles than that of the untreated surface, and formation of AlN compound adds to the surface hydrophobicity enhancements. [ABSTRACT FROM AUTHOR]