A series of dimple-textured surfaces with different geometrical parameters (area density, diameter and depth) were fabricated on the surface of middle carbon steel. And then the friction and wear ...tests were carried out to figure out the main factor that influences the friction and wear properties of the steel surface in non-conformal contact under starved lubricated condition. Furthermore, friction and wear behavior of the textured surfaces were analyzed in the process of wear aim to make a preliminary exploration of the wear-reducing mechanism of laser surface texturing. The results show that the depth of the dimple is the main factor that has a significant effect on the friction and wear properties. The best property was obtained for surfaces textured with a depth of 10 μm, area density of 10% and diameter of 100 μm. In addition, the friction coefficient has obvious characteristics in the different period of friction and wear. It can be divided into three stages which are defined as steady-state, variation-state and dry-friction, respectively. The surfaces textured optimum depths can effectively prolong the steady-state and reducing friction and wear in the variation-state that results in a longer sliding distance in the starved lubrication.
•The changes in chemical composition under starved lubrication and dry sliding conditions are analyzed by EDS and XPS.•The COF of the textured surfaces has obvious characteristics as the staved lubrication regime is transferred to dry friction.•The surface textured with optimum depth can effectively prolong the sliding distance before reaching the dry friction state.
This paper introduces a novel approach to corrosion mitigation using electrodeposited, fractal Ni and NiYSZ coatings. Highly adherent, durable multiscale coatings with fractal dimensions above 1.80 ...were fabricated. Corrosion characteristics of coated plain and etched surfaces of In800H, SS310, SS316 and SS347, in comparison to Ha230, were studied in molten 60% NaNO3 + 40% KNO3 at 600 °C. The corrosion rate of coated Fe-based alloys reduced by up to 68% compared to uncoated alloys and was on par with or lower than the corrosion rate of Ha230. Furthermore, the corrosion-resistant coatings provide for use of low-cost alloys in high temperature corrosive environments.
Linear textures and cross textures with different processing stepovers were fabricated on the surface of GCr15 steel by ultrasonic surface rolling processing (USRP). The effects of texture shape and ...processing stepover on the dry friction and wear performance of the samples were investigated using a ball-and-disk friction tribometer. The results showed that all the USRP texturing samples had lower friction coefficients and wear rates than those of the substrate sample under dry friction conditions. The best tribological performance was achieved at the stepover of 150 μm for linear textures and 250 μm for cross textures. For two shapes of textures with the same stepover, the linear texture had better wear resistance and the cross texture had better friction reduction. The texture shape and processing stepover influenced the texture height and the strengthening effect, which in turn affected the tribological properties of the samples. The improvement in friction and wear performance by ultrasonic rolling texturing was attributed to the synergistic effect of the strengthened substrate, reduced actual contact area, and entrapment of wear debris.
Journal bearings are the most commonly used load elements in rotating systems and have a long history in tribology research. However, the relatively new surface modification technique of femtosecond ...laser texturing has rarely been used to increase the efficiency of journal bearings. We used a 300-fs laser to create chevron-shaped microstructures in different circumferential texture locations on half-bearing shells to investigate the effect of partial texturing on the tribological performance of journal bearings. With a customized shaft-bearing shell setup, the coefficient of friction and lubrication film thickness was tracked in two load scenarios at varying rotational speeds. In fully film conditions, the findings demonstrate that textures in the high-load region of journal bearings provide the highest lubricant film thickness and lowest friction compared to textures in the pressure build-up, divergent zone, and unstructured reference. Moreover, surface textures in the high-load area also perform better in boundary and mixed lubrication. Experimental data have also shown that asymmetric texture designs have a detrimental effect on lubrication performance. In contrast to symmetric designs, the lubrication film build-up is hindered. The research results represent a step toward transferring laboratory findings on laser surface texturing for tribological optimization in real applications.
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•Textures in the high-load region provide the highest lubricant film thickness and lowest friction in hydrodynamic lubrication.•Textures in the high-load area also perform better in boundary and mixed lubrication.•Asymmetric texture designs can be detrimental for the lubrication performance of journal bearings.
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•Hierarchical micro- and nanostructures can be fabricated by ns lasers on Cu.•Microstructures arise from the accumulation of laser-induced resolidified materials.•Surface ...nanostructures originate from the redeposition of laser-induced plasmas.•Enhanced laser-induced evaporation and melting result in complex surface structures.
Hierarchical surface micro- and nanostructures have attracted much attention in recent years due to their important roles in many applications. Among numerous techniques, ultrafast laser surface texturing technology has gained great success in recent years due to its flexibility and controllability in preparing large-area hierarchical micro- and nanostructures on a wide range of metal surfaces. However, recent studies have demonstrated that low-cost nanosecond (ns) lasers are also reliable tools to induce hierarchical micro- and nanostructures formation on metals, but the underlying formation mechanism is not yet understood. In this study, by observing the morphology evolution of surface structures, we proposed that the formation of surface hierarchical micro- and nanostructures originates from the accumulation of laser-induced resolidified materials and the redeposition of laser-induced plume. On one hand, our proposed mechanism explains the effect of laser pulse width on the morphology of surface structures, and, on the other hand, it explains some phenomena observed in other studies, which can benefit potential applications of this technology in different areas.
Based on the material property exhibiting a sublinear dependence of friction on load, a new mechanism of texturing for friction reduction has been identified and explored. In this, the nominal ...contact area is reduced by textures, the load of the non-concave area thus increases, and the friction coefficient is reduced by the sublinear dependence. Non-textured and textured samples were tested by a reciprocating tribometer to obtain the friction coefficient between polytetrafluoroethylene (PTFE) and steel. An empirical equation for the sublinear dependence was found, and used in a numerical mixed lubrication model to evaluate the mechanism. The results show that this mechanism explains well for the friction reduction of textured surface in dry conditions, and is still beneficial under mixed lubrication.
•A new mechanism of texturing for friction reduction is identified, and explored under dry/mixed lubrication conditions.•In this, texturing is used to artificially control the contact pressure distribution, and achieve a lower friction.•This mechanism explains well for the friction reduction of textured surface in dry conditions.•A numerical model is established to evaluate the friction reduction from this mechanism under mixed lubrication.•This mechanism may supplement the hydrodynamic theory to design the texturing appliable in multi lubrication conditions.
The aim of this study is to promote significant bond strength with laser surface texturing tools for different coating deposited by spray processes. Pulsed nanosecond laser has been used to improve ...the ultimate adhesion strength of thermal spray coating designed for specific applications, and the full potential of this technology must be further explored. This technology proposes several benefits such as free of grit-particle inclusions, limited affected zone and the interface contact quality. The most important improvement is the coating anchoring in the substrate by laser patterned surface. Adhesion bond strength has been improved and evaluated with the contact area. Fracture mechanic analysis has been studied and it showed that the pattern morphology has an impact on crack propagation. A mixed-mode failure has been defined and chosen to explain adhesion strength improvements for the different applications. Laser surface texturing was performed on light metal alloys substrates before cold spraying of light metal alloys powder, wire-arc metallization and atmospheric plasma spraying of thermal barrier coating without bond coat. This study has highlighted laser potential to enhance adhesion bond strength in the dry deposition field.
•Our study covers surface laser texturing to enhance coating adhesion strength•This paper focuses on anchoring mechanisms induced by prior surface treatments•Adhesion strength and deposition efficiency were increased for different thermal spray processes with laser surface texturing•A short pulsed laser is used with a low power (20W), a high frequency (varying between 10 and 100kHz) and an adapted wavelength (λ=1064μm)•Bonding mechanisms and failures mode are described for conventional and laser treated samples
Recently, there has been a growing interest in utilizing surface texture to enhance the tribological properties of sliding components. Particularly noteworthy is the application of tool vibration at ...ultrasonic frequencies for efficiently generating surface textures. This study focuses on generating surface texture on the end surface of a stainless steel disk through ultrasonic assisted turning. The mathematical expression of the theoretical texture configuration, derived from the tool trajectory, is closely aligned with the actual machined surface. A novel geometric analysis was conducted to address the challenge of interference between the finished surface and the flank surface, resulting in a reduction in texture height. This analysis revealed that the texture height error from the theoretical value was limited to within 10%. Ball-on-disk tribological experiments were also performed on the textured surface to assess starting friction phenomena. The findings indicated that surfaces with texture exhibited a more minor fluctuation in the starting friction coefficient compared to those without texture. In summary, this paper explores the efficient generation of surface texture on stainless steel disks using ultrasonic assisted turning. Theoretical configurations were mathematically expressed and aligned well with actual machined surfaces. The study also introduced a novel geometric analysis to address interference-related texture height reduction. Moreover, tribological experiments demonstrated that textured surfaces experienced a more stable starting friction coefficient, highlighting the potential of surface texturing for improving tribological properties in sliding components.
•nHSN process achieves surface nanostructures and desired chemistry for extreme wettability.•Nanostructuring mechanism is a combined effect of chemical etching and attachment of functional ...groups.•Wettability is finely tuned by adjusting laser parameters in NLT step and choosing silane reagent in CIT step.•Superhydrophobicity and superhydrophilicity is demonstrated for aluminum, steel and titanium alloys.•nHSN process increases laser-processing rate by two orders enabling large-area processing for practical throughput.
We present a novel nanosecond laser-based high-throughput surface nanostructuring (nHSN) process that can simultaneously create random nanostructures and attain desirable surface chemistry over large-area metal alloy surfaces. nHSN consists of two sequential steps: (1) nanosecond laser texturing (NLT) and (2) chemical immersion treatment (CIT). NLT step in water confinement (wNLT) does not generate topological patterns but preconditions the metal surface chemically and mechanically. Our analysis shows that surface nanostructuring results from a combined effect of chemical etching and attachment of functional groups during the CIT phase of nHSN. A proper silane reagent can be selected for the CIT phase to achieve the desired surface wetting behavior, while laser parameters can also be adjusted during the NLT phase to finely tune the nanostructuring mechanism. nHSN nanostructures with fluorosilane chemistry repel water, while those with cyanosilane chemistry attract water. Extreme wettability including superhydrophobicity and superhydrophilicity is assessed for multiple engineering metal alloys including aluminum, steel and titanium alloys. Compared with existing ultrashort laser-based surface-texturing methods, the nHSN laser scan time represents a significant improvement in processing efficiency and enables a practical throughput for large-area processing of engineering alloys.
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•Fabrication of functional surfaces by water jet guided laser micro-machining.•Stable superhydrophobic property is achieved on stainless steel surfaces.•Surface morphology and ...chemistry define the wettability of metallic surfaces.
This experimental work demonstrates a new cost-effective way of achieving superhydrophobicity on metallic surfaces by micro-texturing with a novel water jet guided laser process. Compared to conventional pure laser texturing by nanosecond, picosecond and femtosecond lasers, water jet guided laser processing yields textures with an almost zero heat affected zone while the debris on the textured surface is simultaneously cleaned by the jet during the process. The effects of grid spacing, laser power coupled into the jet and water jet diameter are examined and processing conditions for achieving superhydrophobicity are provided. Changes in the wetting of the surface over time under ambient conditions from hydrophilic to superhydrophobic, due to changes in surface chemistry, were explored. It has been shown that the surface contact angle dramatically increases within the first couple of days after texturing when exposed to air. After around 20 days, the contact angle stabilized at 150°, 130° and 129° on textured 304 stainless steel, titanium and 6061 aluminum surfaces, respectively.
