Picosecond Laser Surface Research Articles

Manipulation of tribological properties of stainless steel by picosecond laser texturing and quenching

We reported on the manipulation of tribological properties of stainless steel by picosecond laser texturing and quenching. The micro-grooved textures were formed on the steel surface, accompanied with the appearance of nanostructures with grain sized of 80–400nm, oxides thin film (Fe2O3 and Cr2O3) and martensite during picosecond laser surface texturing process. The tribological tests indicated that the average friction coefficients and wear rates of textured surfaces initially increased then decreased with the increase of spacing of micro-grooves. The well-controlled friction and wear properties are attributed to the combined effects of induced micro-/nanostructures, martensitic transformation and oxides thin film in the local quenched zone of stainless steel samples.

Picosecond laser surface micro-texturing for the modification of aerodynamic and dust distribution characteristics in a multi-cyclone system

AbstractAerodynamic flow control in a cyclone is critical to its performance. Dust accumulation in a multi-cyclone is undesirable. This research investigated, the effects of laser-patterned Ethylene-Propylene-Diene Monomer (EPDM) roof in a commercial multi-cyclone system on its aerodynamic and dust accumulation characteristics. Our experimental data show that strategically designed concentric micro-dimples on the cyclone roof can improve both the aerodynamic performance and dust separation capability in the multi-cyclone system. With specific laser-patterned cyclone roof, up to 78% reduction in dust adhesion was demonstrated in one of the cones (cone 9). With the 315-μm diameter micro-dimples on EPDM roof, it was observed that dimples located close to the vortex finder caused an increase in the reverse airflows in the cyclone, thereby effecting entrainment of dust. The overall dust separation efficiency of the multi-cyclone system was at an average of 99.9% with the laser-textured roof, hence no adverse e...

High Power Picosecond Laser Surface Micro-texturing of H13 Tool Steel and Pattern Replication onto ABS Plastics via Injection Moulding

H13 tool steels are often used as dies and moulds for injection moulding of plastic components. Certain injection moulded components require micro-patterns on their surfaces in order to modify the physical properties of the components or for better mould release to reduce mould contamination. With these applications it is necessary to study micro-patterning to moulds and to ensure effective pattern transfer and replication onto the plastic component during moulding. In this paper, we report an investigation into high average powered (100 W) picosecond laser interactions with H13 tool steel during surface micro-patterning (texturing) and the subsequent pattern replication on ABS plastic material through injection moulding. Design of experiments and statistical modelling were used to understand the influences of laser pulse repetition rate, laser fluence, scanning velocity, and number of scans on the depth of cut, kerf width and heat affected zones (HAZ) size. The characteristics of the surface patterns are analysed. The process parameter interactions and significance of process parameters on the processing quality and efficiency are characterised. An optimum operating window is recommended. The transferred geometry is compared with the patterns generated on the dies. A discussion is made to explain the characteristics of laser texturing and pattern replication on plastics.

Picosecond Laser Surface Cleaning of AM1 Superalloy

Laser scanning processing of nickel-based superalloy AM1 surfaces by ultra-short pulses (10 ps) is introduced as a cleaning and deoxidation postprocess. The laser cleaning is investigated with two-directional surface scanning by a laser beam with several frequencies of pulse generation. The EDX elemental analyses of the laser cleaned AM1 surfaces were compared with the non-laser treated surface. The optimal speed, laser pulse repetition frequency, overlapping and layer repetition count are determined for minimal structural changes on the mechanically polished AM1 surfaces. The laser cleaning after shifted laser surface texturing (sLST) is presented as a two-step preparation of a superalloy surface for thermal spraying. The heat accumulation effect and temperature fields are calculated from a semi-planar model of a laser beam scanning heat source. The theoretical results are discussed in comparison with experimental studies. The upper and bottom bounds are defined for an optimal high speed laser cleaning process.

Modification of wettability of stainless steel by picosecond laser surface microstructuring

We report on the modification of the wettability of stainless steel by picosecond laser surface microstructuring in this paper. Compared with traditional methods, picosecond laser-induced surface modification provides a fast and facile method for surface modification without chemical damage and environmental pollution. As a result of treatment by 100 ps laser pulses, microstructures are fabricated on the stainless steel sample surface, contributing to the increase of the contact angle from 88° to 105°, which realizes a transformation from hydrophilicity to hydrophobicity. The morphological features of fabricated microstructures are characterized by scanning electron microscopy and optical microscopy.

Picosecond laser surface micropatterning of ceramics by optical fiber induction

Parallel microgrooves and mesh structure with a line width of about 16 μm, which is much smaller than the diameter of the laser focus spot of 50 μm, are fabricated on Al2O3 ceramic surfaces by picosecond laser patterning with optical fiber induction. The patterned grooves are of high quality without burr, recasting or thermally induced cracks. Grain refinement of the groove surfaces caused by the rapid condensation and redeposition during picosecond laser irradiation with optical fiber induction improved the smoothness and mechanical strength of the grooves. Different patterns can be fabricated by adjusting the optical fiber layout, which is independent of the laser scanning direction. The regions etched by the laser are kept in near-field contact with the optical fibers when the laser beam passes through the fibers and irradiates the ceramic surface. This results in localized field enhancement between the transparent optic fiber and ceramic surface, which produces the precise microgrooves. The developed technique allows high-resolution micromachining of the surfaces of hard and brittle ceramic-type materials.

Combined anodizing and picosecond laser treatment to control the corrosion rate of biodegradable magnesium alloy AZ31

The corrosion rate of magnesium alloys is generally too high for biodegradable implant applications. This work explored combinations of anodizing and picosecond laser surface treatments to modify the corrosion response of magnesium alloy AZ31. Anodizing of the AZ31 in NaOH solutions produced porous oxide layer structures. Shallow laser treatment of these anodized surfaces, using low pulse powers, resulted mainly in oxide ablation and impaired corrosion resistance. Higher pulse power, resulting in rapid melting and resolidification into the substrate, provided an improved corrosion response. The refined grain structure produced is approximately only 5 µm deep and therefore has minimal influence on bulk mechanical properties. It is therefore a suitable process for surface modifications on small medical device structures. Controlling the initial point of degradation has been demonstrated by the use of selective laser treatment of the AZ31 surface.