Design Rules for Laser‐Treated Icephobic Metallic Surfaces for Aeronautic Applications

Results of the work in the Laser4Fun project has been published as:

Vittorio Vercillo, Simone Tonnicchia, Jean‐Michel Romano, Antonio García‐Girón, Alfredo I. Aguilar‐Morales, Sabri Alamri, Stefan S. Dimov, Tim Kunze, Andrés Fabián Lasagni, Elmar Bonaccurso. (2020) Design Rules for Laser‐Treated Icephobic Metallic Surfaces for Aeronautic Applications. Advanced Functional Materials, 1910268.

 

Abstract

Ice accretion on external aircraft surfaces due to the impact of supercooled water droplets can negatively affect the aerodynamic performance and reduce the operational capability and, therefore, must be prevented. Icephobic coatings capable of reducing the adhesion strength of ice to a surface represent a promising technology to support thermal or mechanical ice protection systems. Icephobicity is similar to hydrophobicity in several aspects and superhydrophobic surfaces embody a straightforward solution to the ice adhesion problem. Short/ultrashort pulsed laser surface treatments are proposed as a viable technology to generate superhydrophobic properties on metallic surfaces. However, it has not yet been verified whether such surfaces are generally icephobic under representative icing conditions. This study investigates the ice adhesion strength on Ti6Al4V, an alloy commonly used for aerospace components, textured by means of direct laser writing, direct laser interference patterning, and laser‐induced periodic surface structures laser sources with pulse durations ranging from nano‐ to femtosecond regimes. A clear relation between the spatial period, the surface microstructure depth, and the ice adhesion strength under different icing conditions is investigated. From these observations, a set of design rules can be defined for superhydrophobic surfaces that are icephobic, too.

Link(s)

https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.201910268

PhD degree awarded to Antonio García Girón

On 28th February 2020, our Early Stage Researcher Antonio García Girón, from the Laser4Fun project, successfully defended his thesis for the degree of Doctor of Philosophy.

The work titled “Laser-based surface functionalisation: advances in durability and 3D processing” was carried out in the University of Birmingham under the supervision of Professor Stefan Dimov, studying some limitations of the laser surface functionalisation. The examination board was composed by Dr. C. Kong, Dr. S. Bigot and Dr. N. Gao, and the viva took place at the University of Birmingham in the morning on 28th February 2020.

Summary of Antonio’s research
Surface functionalization is gaining interests for industry and research due to the new attractive properties that can be “imprinted” on metal components, e.g. bacteria repellence or hydrophobicity among others. Considering the available alternative technologies to achieve such functional responses, direct laser writing is gaining a popularity due to its cost-effectiveness, selectivity and relatively short processing time. It allows surface properties to be modified or tuned by patterning and texturing at micron or submicron scales. However, laser surface functionalization has some limitations, too, such as the durability of the produced topographies and hence of their functionality, and also capabilities to apply it on free-form surfaces. In this context, the focus of the research presented in this thesis is on addressing these open issues. In particular, a combination of plasma surface alloying and laser patterning is proposed in order to increase hardness of produced functional surfaces, and thus to increase their wear resistance and durability. Also, a method to study the effects of the process disturbances in patterning 3D surfaces is proposed, especially on resulting topographies and their functional responses. All together, the research advances the knowledge in laser surface patterning and addresses key constraints for the broader use of this technology by industry.

Development of an Analytical Model for Optimization of Direct Laser Interference Patterning

Results of the work in the Laser4Fun project has been published as:

Bogdan Voisiat, Alfredo I. Aguilar-Morales, Tim Kunze and Andrés Fabián Lasagni. Development of an Analytical Model for Optimization of Direct Laser Interference Patterning. Materials 13 (200), 2020.

Abstract

Direct laser interference patterning (DLIP) has proven to be a fast and, at the same time, high-resolution process for the fabrication of large-area surface structures. In order to provide structures with adequate quality and defined morphology at the fastest possible fabrication speed, the processing parameters have to be carefully selected. In this work, an analytical model was developed and verified by experimental data, which allows calculating the morphological properties of periodic structures as a function of most relevant laser-processing parameters. The developed
model permits to improve the process throughput by optimizing the laser spot diameter, as well as pulse energy, and repetition rate. The model was developed for the structures formed by a single scan of the beam in one direction. To validate the model, microstructures with a 5.5 m spatial period were fabricated on stainless steel by means of picosecond DLIP (10 ps), using a laser source operating at a 1064 nm wavelength. The results showed a di erence of only 10% compared to the experimental results.

Link(s)

https://doi.org/10.3390/ma13010200

Award for Vittorio Vercillo at SAE conference

Last June, the SAE International Conference on Icing of Aircraft, Engines, and Structures took place in Minneapolis (USA). New trends, new knowledge, and new solutions were discussed in more than 160 oral presentations that dive into every aspect of icing. Vittorio Vercillo, an Early Stage Researcher (ESR) in the Laser4Fun project, was awarded of the Outstanding Oral Presentation Award, for his contribution “Icephobic Properties of Laser-Treated Superhydrophobic Surfaces”.

More info at: https://www.sae.org/participate/awards/sae-engineering-meetings-board-outstanding-oral-presentation-award

The Role of the Surface Nano-Roughness on the Wettability Performance of Microstructured Metallic Surface Using Direct Laser Interference Patterning

Results of the work in the Laser4Fun project has been published as:

Alfredo I. Aguilar-Morales, Sabri Alamri, Bogdan Voisiat, Tim Kunze and Andrés F. Lasagni. Nano-Roughness on the Wettability Performance of Microstructured Metallic Surface Using Direct Laser Interference Patterning. Materials 2019, 12(17), 2737.

Abstract

Superhydrophobic natural surfaces usually have multiple levels of structure hierarchy, particularly microstructures covered with nano-roughness. The multi-scale nature of such a surface reduces the wetting of water and oils, and supports self-cleaning properties. In this work, in order to broaden our understanding of the wetting properties of technical surfaces, biomimetic surface patterns were fabricated on stainless steel with single and multi-scale periodic structures using direct laser interference patterning (DLIP). Micropillars with a spatial period of 5.5 µm and a structural depth of 4.2 µm were fabricated and covered by a sub-micro roughness by using ultrashort laser pulses, thus obtaining a hierarchical geometry. In order to distinguish the influence of the different features on the wettability behavior, a nanosecond laser source was used to melt the nano-roughness, and thus to obtain single-scale patterns. Then, a systematic comparison between the single- and multi-scale structures was performed. Although, the treated surfaces showed hydrophilic behavior directly after the laser treatment, over time they reached a steady-state hydrophobic condition. However, the multi-scale structured metal showed a contact angle 31° higher than the single-scale geometry when the steady-state conditions were reached. Furthermore, the impact of the surface chemistry was investigated by energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analyses. Finally, a hydrophobizing agent was applied to the laser treated samples in order to further enhance the water contact angles and to determine the pure contribution of the surface topography. In the latter case, the multi-scale periodic microstructures reached static contact angles of 152° ± 2° and a contact angle hysteresis of only 4° ± 2°, while the single-scale structures did not show superhydrophobic behavior. These results definitely suggest that multi-scale DLIP structures in conjunction with a surface chemistry modification can promote a superhydrophobic regime.

Link

https://doi.org/10.3390/ma12172737

Avoiding Starvation in Tribocontact Through Active Lubricant Transport in Laser Textured Surfaces

Results of the work in the Laser4Fun project has been published as:

Tobias Stark , Thomas Kiedrowski, Holger Marschall and Andrés Fabián Lasagni. Avoiding Starvation in Tribocontact Through Active Lubricant Transport in Laser Textured Surfaces. Lubricants 2019, 7(6), 54.

Abstract

Laser texturing is a viable tool to enhance the tribological performance of surfaces. Especially textures created with Direct Laser Interference Patterning (DLIP) show outstanding improvement in terms of reduction of coefficient of friction (COF) as well as the extension of oil film lifetime. However, since DLIP textures have a limited depth, they can be quickly damaged, especially within the tribocontact area, where wear occurs. This study aims at elucidating the fluid dynamical behavior of the lubricant in the surroundings of the tribocontact where channel-like surface textures are left after the abrasion wear inside the tribocontact area. In a first step, numerical investigations of lubricant wetting phenomena are performed applying OpenFOAM. The results show that narrow channels (width of 10 μm) allow higher spreading than wide channels (width of 30 μm). In a second step, fluid transport inside DLIP textures is investigated experimentally. The results show an anisotropic spreading with the spreading velocity dependent on the period and depth of the laser textures. A mechanism is introduced for how lubricant can be transported out of the channels into the tribocontact. The main conclusion of this study is that active lubricant transport in laser textured surfaces can avoid starvation in the tribocontact.

Link(s)

How to Tailor Structural Colors for Extended Visibility and White Light Generation Employing Direct Laser Interference Patterning

Results of the work in the Laser4Fun project has been published as:

Storm, S., Alamri, S., Soldera, M., Kunze, T., Lasagni, A. F., How to Tailor Structural Colors for Extended Visibility and White Light Generation Employing Direct Laser Interference Patterning. Macromol. Chem. Phys. 2019, 1900205. 

Abstract

The appearance of a surface can be controlled by creating periodic microstructures designed to diffract light and produce structural colors. Nevertheless, since structural coloration is based on diffraction, the produced colors have a strong dependence on the viewing angle and absence of coloration takes place while tilting the samples. In this work direct laser interference patterning is used to firstly provide transparent polymer sheets a structural coloration with a high‐range observation angle, and secondly to demonstrate the combination of structural colors, producing a white coloring effect. The employed approaches are based on the fabrication of micro‐gratings with multiple periods in the same structured area and on the engineering of the diffraction orders of the diffraction spectrum. The patterned surfaces are characterized by confocal microscopy and angular spectrometry in reflection mode. The morphological characterization shows homogeneous surface patterns, while the spectral results demonstrate that combining four spatial periods on a single patterned surface, a white appearance is obtained over an angular observation range higher than 30°. The experimental results are supported by theoretical predictions by means of generalized formulas based on the diffraction of light.

Link(s)

Video: Hydrophobiticy of DLIP functionalized surface on stainless steel

The Direct Laser Interference Patterning (DLIP) technique has been used to create a functionalized surface on stainless steel (black area). In combination with an additional post-treatment, the metal surface has extremely water-repellent properties with contact angles of over 150 degrees. The microscopic surface exhibits “miniature mountains” that create a superhydrophobic surface, similar to its natural pendent on a lotus leaf. The sample was placed under water (no wetting of the structured areas is observed) to emphasize the water repellency. Consequently, even if the surface gets wet, it actually stays dry in the laser processed areas. Finally, DLIP allows for self-cleaning properties on technological surfaces at industrially-relevant throughput.