Papers by Keyword: Texturing

Abstract: Laser Surface Texturing (LST) has demonstrated to be the most reliable technique for the micro-modification of surfaces, allowing to obtain taylored surfaces. These modifications, depending on the basic micro-geometry and its repetition pattern, can provide special functionalities to a surface, such as hydrophilicity, hydrophobicity, reflectance, anti-bacterial, ostheo-integrability, as well as custom aesthetic, among others.Nevertheless, when a laser irradiates metallic surfaces, the micro-structure can be modified due to the heat induced, changing the mechanical properties of the surface. To avoid these effects, cold or ultra-short pulsed lasers must be used.A cold laser emits optical pulses with a duration below 1 ps (ultra-short pulses), in the domain of femtoseconds (fs=10^-15 s). These ultra-short pulses, combined with high frequencies, in the megahertz region, leads to pulse trains with high repetition rates. This allows the sublimation of the material, keeping it relatively cold due to the short exposition time to irradiation.Ti6Al4V is the most used Ti alloy, thanks to its excellent weight/mechanical properties ratio. Nevertheless, its tribological behavior is very poor. Although there is intense research to improve it by using LST, the study of the influence of femtosecond laser parameters in the desired micro-geometries is still a gap in the scientific literature.In this research, a study of the influence of power (up to 50 W) and frequency (up to 2 MHz) in the fs-laser texturing of Ti6Al4V is presented. Local pulse repetition, linear and surface textures have been studied by combining power and frequency in these ranges, evaluating the geometry obtained by variable focus microscopy. The study carried out has allowed to determine the optimal set of parameters as a function on the target texture geometry, as well as the range in which the LST removal process changes from sublimation (for texturing) to melting (for micro-machining).

Abstract: This work investigates properties of Poly (3,4-ethylenedioxythiophene)–poly (styrene sulfonate) (PEDOT:PSS) on black silicon (nanotextured) and hybrid textured (nanotextured/microtextured) surfaces. The black silicon (b-Si) surface is fabricated using two-step metal-assisted chemical etching (MACE) process on crystalline silicon (c-Si) while the hybrid textures are fabricated using two-step MACE process on microscale pyramids. With PEDOT:PSS, weighted average reflection (WAR) reduces from 9.2% to 7.7% for b-Si and from 7.2% to 5.2% for hybrid textures. This is due to the anti-reflective (AR) property of the polymer. Electrical characterizations of the PEDOT:PSS layer reveal higher sheet resistance (R_s), lower hole concentration (n_h) and improved mobility (μ_h) with the presence of the surface textures on c-Si, in comparison to the results from planar c-Si reference.

Abstract: Functional surfaces have been widely used for control of physical and/or chemical properties of substances on the surface. In the manufacturing industries, some of micro fabrication approaches such as laser processing have been applied to form textured surfaces, which control the surface functions with topographies. This study presents the surface texturing in cutting with micro-scale structured end mills. Micro-scale nicks are fabricated on the cutting edges of PCD (Poly-Crystalline Diamond) end mills in laser finishing. The cutting operation is conducted to form the chips on each nick with the cutter axis inclination in the feed direction. An analytical model is applied to control the surface structure for the spindle speed, the feed rate, the nick geometry and the inclination angle of the cutter axis. Then, the surface structures were fabricated in the actual cutting process. The machining operation in this study is available in fabrication of the micro-scale structures at high production rates and the structures shape can be controlled in the surface simulation.

Abstract: In this paper, friction behavior of textured carbide and steel surface has been studied in order to investigate the effect of different patterns. Several simple textures have been fabricated using straight groove grinding wheel. By microstructuring, various spacing and height of the structure, we investigate the role of topography in terms of friction characteristic. The change of friction behavior has been tailored by grinding operation using straight grooved wheel and evaluated in terms of friction. Friction values were measured by Tribometer. Frictional properties of textured carbide and steel surfaces were assessed with the help of parallel steel slider with 2000g normal force under dry condition using four different sliding speeds. It is found from the experiment that except 30° and 90° angle patterns, rest of the patterns on carbide surfaces show friction reduction which is roughly from 0.15 to 0.13. On the other hand, similar textured patterns can reduce the COF from 0.17 to 0.13 in case of steel surface.

Abstract: As aircraft and thermoelectric turbine blades work in aggressive environments (high temperatures and pressures), they are exposed to oxidation reactions. Ceramic coatings are employed to increase the turbine work temperature (improving its performance) and a bond coat (BC), base of particulate material of Ni-Cr-Al powders, which assure a good adhesion, gradual decrease in thermal expansion coefficient between the metallic substrate and the ceramic top coat, avoiding the oxidation effect in the metallic substrate. This research aims the study and comparison of two different deposition process routes of particulate materials of BC (MCrAlY) on AISI 316 stainless steel substrate. In the first case, the BC powder was pre-deposited by segregation method and irradiated by a CO₂ laser beam. In the second case, laser surface texturing was done on the stainless steel surface by a Yb: fiber laser beam, the BC was deposited by the same method, and further, irradiated by a CO₂ laser beam. The main focus of this work was to evaluate the resulting interface for both mentioned cases. For this propose, characterizations were made using the techniques of optical microscopy and roughness measurements. In the first case, homogenous layers of bond coat were obtained. Optical microscopy suggest the formation of a metallurgic bonding between the substrate and the MCrAlY. For the laser surface texturing, the surface roughness can be adjusted by the laser beam parameters.

Abstract: The finite element model of double etching pits was established, optical performance of multicrystalline silicon wafer before and after etching was simulated by RF MODULE of COMSOL Multiphysics version 3.5a. Optical characteristic of unetching wafer and acidic textured were compared. It is indicates that acidic textured (double etching pits) has low reflectivity, high power flow Y component , the better light trapping. When the wavelength is 600nm, the maximum and minimum value of surface electric field Z component of acidic textured are 1.9 times and 1.4 times respectively than that of unetching wafer, and two extremum value of surface magnetic field Z component are 2.1 times and 1.9 times respectively than that of unetching wafer. Numerical simulation results of Multi hole model are closely with experimental values, which can guide the practical production.

Abstract: A fast laser texturing technique has been utilized to produce micro/nanosurface textures in Silicon by means of UV femtosecond laser. We have prepared good absorber surface for photovoltaic cells. The textured Silicon surface absorbs the incident light greater than the non-textured surface. The results show a photovoltaic current increase about 21.3% for photovoltaic cell with two-dimensional pattern as compared to the same cell without texturing.

Abstract: In the processing of the mold texture, the traditional chemical etching exits the shortcomings of the pollution and the long processing cycle. This article will introduce 3D laser processing technology to the mold industry, based on the laser etching principle on the metal surface, etch processing can be made in the mold surface. Through theoretical derivation from the 3D laser scanning optical system, the 3D laser scanning hardware system is structured to apply in the mold cavity texturing, the control algorithm has been studied, and finally in the developed laser-etch machine the texturing experimental is performed on the injection molds.

Abstract: This paper presents the results of experimental research on the impact assessment texture on scuffing resistance. The results showed that the texturing increases the resistance to scuffing. Above it has been shown that texture having a smaller surface energy and having a larger volume are more resistant to scuffing.

Abstract: As a renewable, clear and inexhaustible energy, solar energy receives much more attention and has partly substituted traditional energies in many fields. Multi-crystalline silicon plays an important role for its low cost, abundant reserves and excellent photoelectric conversion in solar cells. Mixed acid etching is an effectively method to texture the morphology on the surface of mc-Si, While stochastic etching between silicon and acids results in irregular texturing and high reflectivity. In this paper, ultrasonic standing wave is introduced into acid solution, which aid wet etching to texture on the surface of mc-Si by controlling distribution of atoms of acids. Scanning electron microscope experiment shows that the morphology on the surface of mc-Si textured by this method is similar to that of mono-crystalline silicon. And the average reflectivity is 8%, much lower than mixed acid etching.