Laser Textured Stainless Steel Research Articles

Owens-Wendt Method for Comparing the UV Stability of Spontaneous Liquid-Repellency with Wet Chemical Treatment of Laser-Textured Stainless Steel.

The liquid-repellent properties of AISI 304 stainless steel surfaces textured with a femtosecond laser were studied, both after spontaneous hydrophobization and when treated with stearic acid and octyltrimethoxysilane. Surface topography has been shown to play a critical role in determining these properties. Although textures containing only LIPSS exhibited poor liquid-repellency, the performance was significantly improved after engraving the microtexture. The most effective topography consisted of 45 µm-wide grooves with a pitch of 60 µm and protrusions covered with a rough microcrystalline structure. Liquid-repellency, chemical treatment efficiency, and UV resistance were compared using derived Owens-Wendt parameters. The surface of femtosecond-laser-textured steel after spontaneous hydrophobization was found to be significantly less stable under UV irradiation than surfaces treated with stearic acid or octyltrimethoxysilane modifiers.

Tribological Evaluation of Vegetable Oil/MoS2 Nanotube-Based Lubrication of Laser-Textured Stainless Steel.

In the present work, the functionalisation of austenitic stainless steel, AISI 316L surfaces via nanosecond Nd:YAG laser texturing in order to modify the surface morphology with crosshatch and dimple patterns is presented. A tribological analysis under lubrication with sunflower and jojoba oil with and without the addition of a solid lubricant, MoS2 nanotubes, was performed. In conjunction with friction/wear response laser-textured surface wettability, oil spreadability and oil retention capacity were also analysed. It was shown that the crosshatch pattern generally exhibited lower friction than the dimple pattern, with the addition of MoS2 nanotubes not having any significant effect on the coefficient of friction under the investigated contact conditions. This was found in addition to the better oil spreadability and oil retention capacity results of the crosshatch-textured surface. Furthermore, texturing reduced the wear of the stainless-steel surfaces but led to an approximately one order of magnitude larger wear rate of the steel counter-body, primarily due to the presence of hard bulges around the textured patterns. Overall, the crosshatch pattern showed better oil retention capacity and lower friction in combination with different vegetable oils, thus making it a promising choice for improving tribological performance in various environmentally friendly applications.

Analyte enrichment and sensitive detection over nanosecond laser textured stainless steel superhydrophobic surfaces

In this report, we have investigated the use of nanosecond laser texturing produced superhydrophobic surfaces for enrichment and sensitive detection of analytes. We have shown that by carefully choosing the laser processing parameters, the superhydrophobic surfaces capable of maintaining a small (5 μL) aqueous droplet in spherical shape till the last stage of evaporation and hence enabling the droplet to deposit its entire content over ∼80–100 μm size residual spot upon complete evaporation, can be prepared. The spot was found to get formed by bridging over the micro structures suggesting that the droplet remained suspended over the structures i.e. did not penetrate the structures till the very end of the evaporation process. By performing fluorescence spectroscopy of the residual spot, Rhodamine 6G could be detected at an ultra-low concentration of 10−18 molL−1 in a 5 μL water droplet. When compared with the results obtained on unprocessed stainless steel substrate, these superhydrophobic steel surfaces were found to provide four orders of magnitude enhancement in the lowest detectable concentration of Rhodamine 6G.

Effects of metal film coatings on surface properties of laser-textured stainless steel

Stainless steel substrates were textured with a checkboard pattern by a NIR laser with different scan pitches and laser powers. The as-textured surfaces were found to be hydrophilic. However, after holding in air for 7–15 days, the surfaces exhibited strong superhydrophobicity with contact angles close to 150° due to a reduction in the oxygen content. Thin-film Ag, Cu, Zn and Al coatings were deposited on the textured surfaces. The as-sputtered Ag and Cu films improved the hydrophobicity of the as-textured surface. However, the as-sputtered Zn and Al coatings increased the hydrophilicity. For all of the coatings, the hydrophobicity improved after aging in air for 7– 15 days. Furthermore, all of the coatings enhanced the corrosion resistance of the textured surface. Overall, the results indicate that laser texturing followed by thin-film metal deposition provides a feasible means of tuning both the wettability and the corrosion resistance of stainless steel surfaces.

Tribological behavior of polydopamine/polytetrafluoroethylene coating on laser textured stainless steel with Hilbert curves

Shallow Hilbert curve patterns with easily programmable texture density were selected for laser texturing of stainless steel substrates. Two different texture path segment lengths (12 and 24 µm) and four different laser power percentages (5%, 10%, 15%, and 20%) were investigated. The textured and smooth substrates were coated with thin polydopamine/polytetrafluoroethylene (PDA/PTFE) coatings for tribological property assessment. The effects of texture density (texture area coverage) and laser power on the durability and friction of the coated surfaces were studied. Laser texturing the substrates improved the coating durability up to 25 times, reduced the friction coefficient, and prevented coating global delamination. The textures fabricated with a laser power of 15% and a texture path segment length of 12 µm yielded the best coating durability. The textures provided the interlocking for the PTFE coating and thus prevented its global delamination. Furthermore, the PTFE inside the texture grooves replenished the solid lubricant worn away in the wear track and prolonged the coating wear life.

Laser surface texturing of both thin polytetrafluoroethylene coatings and stainless steel substrates for improving tribological properties

Hilbert curve patterns were laser-textured on both stainless steel substrates and polytetrafluoroethylene (PTFE) thin coatings by applying 15% and 5% of the 2.3-W full laser power, respectively. The nanomechanical and tribological behavior of both smooth and laser-textured PTFE coatings on both smooth and laser-textured stainless steel substrates were studied. It was found that laser-texturing thin PTFE coatings reduced the hardness of PTFE coatings and prevented the coating from tearing under nanoindenter scratches. Furthermore, laser-texturing on both PTFE coatings and the stainless steel substrate improved the coating wear life 29 times compared to the wear life of the control sample without any laser textures.

The Effect of Dimple Overlap on Wettability and Corrosion Resistance of Laser-Textured Stainless Steel

During the laser surface texturing process, scanning overlap is usually misused, because it cannot only be dimple overlap, but also can be laser spot overlap. Experiments were conducted to investigate the relationship between laser spot overlap and dimple overlap during laser surface texturing. Moreover, the effect of dimple overlap on the laser textured microstructures, wettability, and corrosion performances of stainless steel was analyzed. The results have shown that, due to changing radiation conditions, the dimple diameter and dimple overlap varied in a non-linear way with the increase in laser spot overlap. Furthermore, the variation of dimple overlap rather than laser spot overlap had a direct effect on roughness, wettability, and corrosion resistance. When the dimple overlap was greater than 55%, the surface reached the superhydrophobic state and the maximum apparent contact angle was 162.6°. When the dimple overlap was 83.52%, due to passivation layer formed by laser remelting deposition and oxides compaction, corrosion current density was 2.8 × 10−8 A·cm−2, which was 4% of the original value. Consequently, it was determined that it is easier to control the surface roughness, wettability, and corrosion resistance via dimple overlap rather than laser spot overlap in laser surface texturing process.

Influence of gas environment on the dynamics of wetting transition of laser-textured stainless steel meshes

We analyze the role of surrounding gas and aging in ambient air in the wettability behavior of laser-processed stainless steel meshes. Laser texturing of meshes was carried out in the presence of different gases (N2, O2, CO2, Ar, and SF6) in ambient atmospheric air and under different vacuum conditions. The influence of each gas on the evolution of the wettability properties after aging in ambient air is analyzed. The effects of low-pressure and vacuum aging allowed transforming the initial superhydrophilic characteristics of the laser-structured meshes to an almost superhydrophobic state.

Nanosecond laser induced glass particle deposition over steel mesh for long-term superhydrophilicity and gravity driven oil water separation

In this report we show that the laser textured stainless steel meshes which serve as excellent oil water separator immediately after laser processing, lose their oil water separation capability after storage in ambient air. This was possibly due to the reactive nature of the metal oxides formed during laser processing which resulted in transition of the wettability of processed metallic meshes from superhydrophilic to superhydrophobic during storage. To overcome this issue, we show that by using a glass cover plate over the metal mesh during laser processing, micron/submicron sized glass particles can be deposited on to the mesh via a process known as laser induced plasma assisted ablation. Since the glass is inherently hydrophilic and inert, and therefore the glass particles coating produced a stable superhydrophilic/underwater-superoleophobic surface which was observed to maintain its superhydrophilicity for the tested duration of ~8 months and perform oil/water separation with an efficiency of ~96% for various oils. Further, the glass particles coated mesh was found to sustain several cycles of sandpaper abrasion before losing its oil water separation capability.

Effects of mould wear on hydrophobic polymer surfaces replicated using plasma-treated and laser-textured stainless steel inserts

ABSTRACT The mass production of polymeric parts with functional surfaces requires economically viable manufacturing routes. Injection moulding is a very attractive option, however, wear and surface damage can be detrimental to the lifespan of replication masters. In this research, austenitic stainless steel inserts were hardened by low temperature plasma carburising and then different micro and nano scale surface textures, inspired by Lotus leaves and Springtail skins, were laser fabricated. A commonly available talc-loaded polypropylene was used to produce 5000 replicas and thus to investigate the evolution of surface textures both on inserts and replicas together with their functional response. The progressive wear or surface damage on the inserts during the injection moulding process had a clear impact on surface roughness and peak-to-peak topographies of the replicas. In general, polymer replicas produced with the carburised inserts retained wetting properties for longer periods compared with those produced with the untreated replication masters.

Mechanical abrasion resistant candle soot based superhydrophobic coating over nanosecond laser textured stainless steel

In this report, we show that using naturally hydrophobic wax bound carbon soot nanoparticles (WCN) as fillers over laser ablation textured stainless steel surface, a mechanical abrasion resistant superhydrophobic (SH) surface can be prepared. The abrasion resistance may be due to the fact that during mechanical abrasions, the WCN lying in the lower layers of the laser textured surface get spread over the abraded surfaces and maintain superhydrophobicity. Further, the laser created grooves provide a space for the WCN to stay protected from abrasions so that all the WCN do not get wiped away at once. The developed SH surface when abraded by a sandpaper of 3000 grit loaded with 8 kPa load was found to exhibit ∼157° contact angle and ∼7° sliding angle even after 40 cycles of abrasions which corresponded to ∼400 mm abrasion distance. Further, the SH surface obtained by using WCN over laser textured surface was also found to have better abrasion resistance when compared with the SH surface prepared via the conventional fluorosilane coating over laser textured surface.

Simple and fast surface modification of nanosecond-pulse laser-textured stainless steel for robust superhydrophobic surfaces

Superhydrophobic surfaces have been extensively studied for their unique low water adhesion. However, surface robustness and manufacturing difficulties are barriers to widespread use of superhydrophobic surfaces. In this study, a simple and fast surface modification of short-pulse laser-textured surface is developed for a robust superhydrophobic surface. Normally, short-pulse laser-textured surfaces can become superhydrophobic, but require toxic chemical coating, prolonged aging in air, or heat treatment for several hours. In our method, with only 10 minutes of heat treatment with non-toxic silicone oil, the nanosecond-pulse laser-textured stainless steel surface becomes superhydrophobic and shows good robustness.

Short- and Long-Term Wettability Evolution and Corrosion Resistance of Uncoated and Polymer-Coated Laser-Textured Steel Surface

We present the results of one year observation of wetting and corrosion properties of nanosecond fiber laser-textured stainless steel, uncoated and coated with epoxy or FAS (fluoroalkylsilane)-TiO2/epoxy. A comparative study was performed on samples kept under ambient conditions and in reduced air pressure and humidity. The results show the ability to induce wettability conversion from initially superhydrophilic to final superhydrophobic state either indirectly by ageing the uncoated laser-textured surface or directly by application of FAS-TiO2/epoxy coating. The storage conditions significantly influenced the wettability development of uncoated laser-textured steel, i.e., the process of ageing was slowed down in reduced air pressure and humidity. Detailed surface chemical analysis revealed that adsorption of the organic matters from the surrounding media influences the wettability conversion and ageing. However, the ageing of the coated surfaces was not affected by the storage conditions. Corrosion stability of uncoated laser-textured surfaces was enhanced over time due to the wettability transition, depending on their morphology. Coatings represent a superior barrier over the texture and wettability with the stable long-term surface protection against aggressive media.

Picosecond Laser-Textured Stainless Steel Superhydrophobic Surface with an Antibacterial Adhesion Property.

The pursuit of antibacterial properties on the surfaces of food container, medical equipment, and pharmaceutical tanks has been a compelling challenge for decades. Inspired by the biomimetic superhydrophobic surfaces that have self-cleaning, antifog, antisnow, and reduced bacterial adhesion properties, we use a simple and effective technology of a picosecond laser texturing for the fabrication of a superhydrophobic antibacterial surface on AISI 420 martensitic stainless steel plates. The laser-textured surface with micropapillae patterns with superimposed nanostructures exhibits outstanding in-air superhydrophobic and superaerophilicity underwater, which under the oscillation state resists an adhesion of 99% Escherichia coli and 93% Staphylococcus aureus and has hardly any bacterial adhesion under a stationary state. The comparative experiments verify that the robust air layer and hierarchical micro-nanostructures have come together to comprise the antibacterial mechanism. The laser-textured superhydrophobic surface also exhibits superior anticorrosion and antidestructive abilities with excellent antibacterial durability especially if deep cleaning is carried out after each dipping time in the bacterial suspension, promoting its leading-edge applications in medical, food, and pharmaceutical fields.

Short and long term surface chemistry and wetting behaviour of stainless steel with 1D and 2D periodic structures induced by bursts of femtosecond laser pulses

We investigate the short and long term wettability of laser textured stainless steel samples in order to better understand the interplay between surface topography and chemistry. Very different 1D and 2D periodic as well as non-periodic surface patterns were produced by exploiting the extreme flexibility of a setup consisting of five rotating birefringent crystals, which allows generating bursts of up to 32 femtosecond laser pulses with fixed intra-burst delay of 1.5 ps. The change of the surface morphology as a function of the pulse splitting, the burst polarization state and the fluence was systematically studied. The surface topography was characterized by SEM and AFM microscopy. The laser textured samples exhibited, initially, superhydrophilic behaviour which, during exposure to ambient air, turned into superhydrophobic with an exponential growth of the static contact angle. The dynamic contact angle measurements revealed a water adhesive character which was explained by XPS analyses of the surfaces that showed an increase of hydrocarbons and more oxidized metal species with the aging. The characteristic water adhesiveness and superhydrophobicity of laser textured surfaces can be exploited for no loss droplet reversible transportation or harvesting.

Drag reduction effect of ultraviolet laser-fabricated superhydrophobic surface

ABSTRACT Superhydrophobic (SH) surface has been found effective for drag reduction in wall-bounded turbulence for decades, especially the metallic durable SH surfaces are believed very promising for improving the velocity and voyage of marine vehicles. We present stainless steel SH surfaces with U-groove patterns that fabricated by ultraviolet laser texturing and coating modifier treatment. The drag-reducing effects of the SH surfaces are tested by a self-built gravity sliding speed improving evaluation device. The results show that the different drag-reduction performance of the SH surfaces can be achieved by adjusting the line spacing of the crossing U-groove patterns. With the line spacing equalling to 80 μm, the ultraviolet laser textured stainless steel SH surface acquires the static contact angle of 161.5° and the dynamic sliding angle of only 2°, which leads to the maximum speed improving rate of 29.7%.

Influence of stainless steel surface properties on whey protein fouling under industrial processing conditions

Heat-induced fouling is a financial and environmental burden for food and dairy industries and its control is therefore desperately needed. A better understanding of the fouling mechanisms and their relation to stainless steel surface properties is thus of considerable interest. This work aims at studying the impact of stainless steel's surface morphology and surface free energy on fouling by a model dairy solution by a close examination of the deposit's growth and adhesion at the substrate-fluid interface. Pristine model surfaces of controlled roughness and surface energy, i.e. native, mirror polished and biomimetic femtosecond laser textured stainless steel surfaces, fluorosilanized or not, were tested under isothermal conditions in a pilot pasteurization facility fed with a model dairy fluid (whey protein and calcium solution). Multi-scale characterizations of those surfaces before and after fouling, using a wide range of analytical tools (goniometry, SEM, ToF-SIMS, EPMA X-Ray mappings) allowed for a better comprehension of the impact of surface energy and morphology modifications on the fouling behavior while highlighting their complex interactions in fouling governance. Lower surface energy was shown to be an asset against deposit growth, as fluorosilanization of native stainless steel allowed to reduce fouling by 72% (wt.%). The relative sizes of surface relief versus fouling agents has been found crucial, as it impacts interlocking phenomena. Textured surfaces have shown a tremendous increase in fouling (+391% for textured, +86% for fluorosilanized textured). However, interesting fouling performances were obtained on smooth, hydrophobic surfaces, as a reduction by 83% of fouling weight was achieved with fluorosilanized polished samples.

Controlling the stainless steel surface wettability by nanosecond direct laser texturing at high fluences

This work investigates the influence of the direct laser texturing at high fluences (DLT-HF) on surface morphology, chemistry, and wettability. We use a Nd:YAG laser (λ = 1064 nm) with pulse duration of 95 ns to process stainless steel surface. The surface morphology and chemistry after the texturing is examined by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD), while the surface wettability is evaluated by measuring the static contact angle. Immediately after the texturing, the surface is superhydrophilic in a saturated Wenzel regime. However, this state is not stable and the superhydrophilic-to-superhydrophobic transition happens if the sample is kept in atmospheric air for 30 days. After this period, the laser-textured stainless steel surface expresses lotus-leaf-like behavior. By using a high-speed camera at 10,000 fps, we measured that the water droplet completely rebound from this superhydrophobic surface after the contact time of 12 ms.

Transition from superhydrophilic to superhydrophobic state of laser textured stainless steel surface and its effect on corrosion resistance

This work investigates the evolution from superhydrophilic to superhydrophobic surface state on corrosion behaviour of SS316L produced by Nd:YAG nanosecond direct laser texturing (DLT). Results confirm perfect correlation among wettability and corrosion, hence superhydrophobic surface with a contact angle of 168±3.0° reflects in enhanced passivity, lower anodic dissolution and corrosion current reduction. Characterization of the corrosion attack by 3D microscopy reveals high sensitivity of superhydrophilic surfaces on corrosion propagation direction in regard to the laser beam passage (90°/0°). However, this trend completely diminishes with superhydrophobic development. Further, DLT also completely prohibits intergranular corrosion detected with the non-processed sample.

Evaluation of enhanced nucleate boiling performance through wall-temperature distributions on PDMS-silica coated and non-coated laser textured stainless steel surfaces

Nucleate boiling was examined on Joule heated stainless steel foils, functionalized by PDMS-silica coating and/or nanosecond-laser texturing. The nucleating bubbles and transient temperature fields were visualized through high-speed IR and video recordings. The differences in boiling performance were evaluated through wall-temperature distributions. Results confirmed that smooth surfaces require high activation temperatures and produce larger bubbles, while wall-temperature distributions display higher standard deviations, higher local superheats, and bimodal shapes. Similarly, relatively high activation temperatures were observed on the superhydrophilic surface, where the enhanced liquid replenishment on the active nucleation sites reduces the bubble departure diameters and prevents formation of local hotspots. Consequently, the analyzed temperature distributions have negative skewness and decreased standard deviation. The highest heat transfer coefficient was achieved on a laser textured surface with non-uniform wettability and multi-scale microcavities. Here, nucleation site density was as high as 200cm−2 at 300kW/m2, while wall-temperature distributions demonstrated by far the lowest standard deviation. The temperature distributions also proved that annealed PDMS-silica coating significantly increased the thermal resistance of the entire heater. On the contrary, laser textured surfaces provided an even better boiling performance compared to coated surfaces and did not increase heater’s thermal resistance. This additionally endorses the coating-free, direct laser texturing method as a cutting-edge technology in the development of surfaces capable of significantly enhanced boiling heat transfer.