Effects of Laser Surface Texturing and Lubrication on the Vibrational and Tribological Performance of Sliding Contact

Various textures are fabricated by a picosecond laser machine on the surfaces of circular stainless steel specimens. Vibrational and tribological effects of laser surface textures are investigated by means of a tribometer and a data acquisition and signal processing (DASP) system. Experimental results show that surface textures can reduce the coefficients of friction (COFs), enhance the wear resistance, and improve the dynamical performance of frictional surfaces. In this study, the surface with micro circular dimples in diameter of 150 μm or textured area density of 25% has the best tribological and dynamical performance. Compared with the non-textured surface, the surface with circular dimples in diameter of 150 μm and 15% textured area density has 27% reduction of COFs, 95% reduction of frictional vibrations, and 66% reduction of frictional noise. The frictional vibrations and noise in the sliding contacts can be effectively reduced by adding graphene to the lubrication oil, and the surface textures enhance the frictional noise reduction performance of lubrication.

A Novel Process for Manufacturing High-Friction Rings with a Closely Defined Coefficient of Static Friction (Relative Standard Deviation 3.5%) for Application in Ship Engine Components

In recent years, there has been an increased uptake for surface functionalization through the means of laser surface processing. The constant evolution of low-cost, easily automatable, and highly repeatable nanosecond fibre lasers has significantly aided this. In this paper, we present a laser surface-texturing technique to manufacture a surface with a tailored high static friction coefficient for application within driveshafts of large marine engines. The requirement in this application is not only a high friction coefficient, but a friction coefficient kept within a narrow range. This is obtained by using nanosecond-pulsed fibre lasers to generate a hexagonal pattern of craters on the surface. To provide a suitable friction coefficient, after laser processing the surface was hardened using a chromium-based hardening process, so that the textured surface would embed into its counterpart when the normal force was applied in the engine application. Using the combination of the laser texturing and surface hardening, it is possible to tailor the surface properties to achieve a static friction coefficient of ≥0.7 with ~3–4% relative standard deviation. The laser-textured and hardened parts were installed in driveshafts for ship testing. After successfully performing in 1500 h of operation, it is planned to adopt the solution into production.

STATE OF THE ART OF SURFACE TEXTURING FOR BIOTRIBOLOGY APPLICATIONS

Surface texturing can be defined as a technique that consists of creating micro cavities in the surface of a material. There are different texturing techniques such as chemical etching, electromechanical micromachining, diamond embossing, electric discharge, pellet-pressing and laser surface, the last being the most common. For years, these surface texturing techniques have been used in tribological applications because microcavities can store oils or fluids and constantly lubricate the surfaces that are subjected to wear; they can also be used to trap wear particles (debris) that would otherwise act as abrasive particles (three body abrasive wear). This literature review seeks to analyse and compare the advantages that the use of surface texturing techniques can offer in reducing the wear of prosthetic components and therefore lengthening their useful life, to provide a better quality of life to patients. The results of this review showed a growing interest in the scientific community in the use of surface texturing for biotribogical applications, using to a greater extent the Laser Surface Texturing (LST) technique and the surface pattern composed by dimples.

Laser Texturing for Superwetting Titanium Alloy and Investigation of Its Erosion Resistance

Erosion of materials is one of the major causes that lead to the malfunction of equipment and facilities, and surface texturing can be a solution for enhancement of erosion resistance. In this work, superwetting (superhydrophilic/superhydrophobic) titanium (Ti) alloy surface with periodic microstructure was prepared by a facile laser-based surface texturing approach which combines laser surface texturing and low-temperature annealing. The effect of laser-induced surface texture and wettability on the erosion resistance of the laser textured surface was studied. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to analyze the chemical surface microstructure and surface on the untreated and laser textured surfaces. The hardness and contact angle of the untreated surface, superhydrophilic surface and superhydrophobic surface were measured by microhardness tester and contact angle goniometer. Using an in-house built erosion experimental setup, the erosion resistance of the untreated surface, superhydrophilic surface and superhydrophobic surface was investigated. The experimental results demonstrate that micro-bumps are formed after laser surface texturing. In the meantime, the surface hardness for the laser textured surface with a step size of 150 μm is increased by 48% under the load of 1.961 N. Compared with the untreated surface, the erosion resistance is increased by 33.9%, 23.8% and 16.1%, respectively, for the superhydrophobic surface. The SEM results show that the untreated surface has large and deep impact pits, while the superhydrophobic surface only has small and shallow impact pits, indicating that the erosion process resulted in less damage to the substrate. The EDS results shows that superhydrophobicity plays a critical role in protecting the substrate from erosion. It is thus believed that the superhydrophobic surface has pronounced effects for improving the hardness and erosion resistance of Ti alloy.

Vacuum brazing of titanium alloy to stainless steel enhance by fiber laser surface texturing

A method for improving the brazing joining strength of Titanium alloy/Stainless steel fabricated through fibre laser surface texturing is introduced because it is a simple process that does not require the fabrication of complicated interlayers. However, previous research shows that a milimeter scale was fabricated by surface modification for dissimilar brazing join, yielding insignificant results and limiting the application and degree of enhancement. Fiber laser ablation was used in this study to create microscale periodic patterns (grooves) on a stainless steel surface. No defect or damage induced during laser surface texturing process. The groove dimension was tunable by controlling the laser parameters. Vacuum brazing of Ti6Al4V to 316L stainless steel with surface texturing, the average joint strength was 22.1 MPa, 34% of increase of joining strength compared to unprocessed flat surface. The combination of laser surface texturing and brazing proven effectively on joining strength enhancement.