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

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.can reduce dramatically lift and increase drag, influencing the maneuverability of the aircraft. Ice protection systems (IPS) are installed to allow aircraft flying safely in icing conditions. At the present time, IPS are not supported by coatings or surfaces that facilitate the ice removal-due to the still too low maturity and robustness of such technological solutions. Yet, surface functionalization is a promising strategy for manufacturing icephobic surfaces [3] aiming to delay ice accretion and/ or to reduce ice adhesion [4,5] and therefore to reduce the electrical or thermal energy required by the IPS.In the last two decades, several approaches for producing icephobic surfaces were presented in literature. For example, it has been proven that polishing the surfaces can reduce the mechanical interlocking with the accreted ice, hence facilitating the ice removal. [5] Coatings can lower the surface free energy and thus reduce the strength of the bonding between ice and surface. [6] On slippery liquid-infused porous surfaces the supercooled water droplets impinge on a liquid instead of a solid surface, which offers a double advantage: interfacial slippage of water or ice occurs (nonzero slip velocity)-which reduces ice adhesion [7] -and interlocking of ice with a liquid interface cannot occur. However, employing coatings or chemicals to

Quo Vadis LIPSS?—Recent and Future Trends on Laser-Induced Periodic Surface Structures

“…Other applications and of LIPSS that are currently explored are: Biomimetic surfaces: Nature provides many highly optimized surface functionalities that may be transferred to technical applications via tailored laser-processing, including LIPSS. Examples are dirt-repellent surfaces through the well-known lotus effect, anti-icing [ 57 , 58 ], the directional transport of liquids inspired by moisture-harvesting lizards [ 59 ] and bark bugs [ 60 ], antiadhesive surfaces inspired by cribellating spiders [ 61 ], or antibacterial [ 62 , 63 , 64 , 65 , 66 , 67 ], cell-repellent [ 68 ], and cell-stimulating/-adapting surfaces [ 69 , 70 , 71 ] for medical applications [ 72 ]. A detailed review of the laser engineering of biomimetic surfaces is provided in [ 6 ].…”

Bioinspired Superhydrophobic Surfaces via Laser-Structuring

“…One-dimensional micrograting structures generally need one exposure and twodimensional micrograting structures (i.e., micropillar arrays) need two exposures with a holding stage rotated by a certain angle (such as 60 • or 90 • ) (Abid et al, 2017). Therefore, DLIP has more potential applications than the other two methods, for applications such as icephobic metallic surfaces in aeronautics (Vercillo et al, 2020). Targeted on metal substrates, a series of superhydrophobic surfaces have been achieved using DLIP or combined laser structuring methods.…”

“…The incident lasers were IR pulsed lasers with a wavelength of 1,064 nm, a pulse duration of 10 ps, and a repetition rate of 1 kHz. Titanium substrate (Ti64) was also explored and structured into micropillars with spatial wavelengths of both 2.7 and 5.4 µm (Vercillo et al, 2020). It should be noted that it is also likely that the LIPSS will be formed simultaneously during the DLIP process (Vercillo et al, 2020), as shown by Figures 1e-h.…”

“…Titanium substrate (Ti64) was also explored and structured into micropillars with spatial wavelengths of both 2.7 and 5.4 µm (Vercillo et al, 2020). It should be noted that it is also likely that the LIPSS will be formed simultaneously during the DLIP process (Vercillo et al, 2020), as shown by Figures 1e-h. The LIPSS with nanoscale spatial wavelengths have enriched the complexity of DLIPpatterned hierarchical structures and hence give rise to the overall surface roughness and superhydrophobicity.…”

Large-Beam Picosecond Interference Patterning of Metallic Substrates

“…Direct laser interference patterning (DLIP) provides a solution to these issues by overlapping two or more coherent laser beams on the surface to directly imprint an interference pattern. If enough pulse energy is used, a large variety of materials can be processed at interference maxima positions, including metals [ 16 , 17 , 18 ], dielectrics [ 19 , 20 ], and even composite materials [ 21 ]. This allows the patterning of an area on the order of several tens of µm in diameter in a single irradiation step and with resolutions below the diffraction limit of the initial beam.…”