scholarly journals Influence of laser hardening on laser induced periodic surface structures on steel substrates

2021 ◽  
Vol 1135 (1) ◽  
pp. 012024
Author(s):  
Lewin Rathmann ◽  
Tim Radel
Keyword(s):  
Thermal Load ◽  
Laser Power ◽  
Contact Angles ◽  
High Ratio ◽  
Laser Hardening ◽  
Surface Structures ◽  
Single Droplet ◽  
Periodic Surface ◽  
Structured Surfaces ◽  
Steel Substrates

Abstract Laser-induced periodic surface structures (LIPSS) are used to structure surfaces for functionalization. Thus, hydrophilic states are generated using LIPSS. However, these nanostructures do not withstand mechanical loads and therefore cannot be used for most tribological applications. Within this work the approach of laser hardening of LIPSS is investigated. It is shown that laser hardening leads to an alteration of prior structured surfaces. That effects the wetting behaviour. The higher the laser power during hardening, the more increases the contact angle of a single droplet on the surface and the more the surface lacks in terms of wetting behaviour. This phenomenon is attributed to changes in LIPSS’ aspect ratio. A high ratio leads to low contact angles and is shifted to low values when the laser power increases resulting in high contact angles. Hence, it is concluded that the thermal load during laser hardening, and it’s influence on the wettability must be taken into account when LIPSS are subjected to laser hardening.

Flexographic ink-coating interactions: effects of latex variations in coating layers

TAPPI Journal ◽  
2016 ◽  
Vol 15 (4) ◽  
pp. 253-262 ◽  
Author(s):  
ERIK BOHLIN ◽  
CAISA JOHANNSON ◽  
MAGNUS LESTELIUS
Keyword(s):  
Contact Angles ◽  
High Ratio ◽  
Print Quality ◽  
Particle Sizes ◽  
Mixed Composition ◽  
Coating Surface ◽  
Covered Area ◽  
Surface Optical ◽  
Flexographic Printing ◽  
Coating Formulation

The effect of coating structure variations on flexographic print quality was studied using pilot-coated paperboard samples with different latex content and latex particle sizes. Two latexes, with particle sizes of 120 nm and 160 nm, were added at either 12 parts per hundred (pph) or 18 pph to the coating formulation. The samples were printed with full tone areas at print forces of 25 N and 50 N in a laboratory flexographic printing press using a waterbased ink. A high ratio of uncovered areas (UCAs) could be detected for the samples that contained 18 pph latex printed at a print force of 25 N. UCAs decreased with increased print force and with decreased amounts of latex in the coating formulation. The fraction of latex covered area on the coating surface was estimated to be 0.35–0.40 for the 12 pph, and 0.70–0.75 for the 18 pph samples. The ink penetration depth into the coating layer could be linked to the fraction of latex-free areas on the coating surface. Optical cross section microscopy indicated that a higher printing force did not increase the depth of penetrated ink to any greater extent. Higher printing force did increase contact between plate and substrate, leading to an improved distribution of the ink. This, in turn, increased print density and decreased UCAs. On closer inspection, the UCAs could be categorized as being induced by steep topographic changes. When appearing at other locations, they were more likely to be caused by poor wetting of the surface. To understand the wetting behavior of the coating surface, observed contact angles were compared with calculated contact angles on surfaces of mixed composition.

Formation of laser-induced periodic surface structures on different materials: fundamentals, properties and applications

2020 ◽  
Vol 9 (1-2) ◽  
pp. 11-39 ◽  
Author(s):  
Stephan Gräf
Keyword(s):  
Friction And Wear ◽  
Review Paper ◽  
Laser Wavelength ◽  
Single Step ◽  
Surface Structures ◽  
Direct Writing ◽  
Periodic Surface ◽  
Experimental Approaches ◽  
Ordered Nanostructures ◽  
Physical Background

AbstractThe use of ultra-short pulsed lasers enables the fabrication of laser-induced periodic surface structures (LIPSS) on various materials following a single-step, direct-writing technique. These specific, well-ordered nanostructures with periodicities in the order of the utilised laser wavelength facilitate the engineering of surfaces with functional properties. This review paper discusses the physical background of LIPSS formation on substrates with different material properties. Using the examples of structural colours, specific wetting states and the reduction of friction and wear, this work presents experimental approaches that allow to deliberately influence the LIPSS formation process and thus tailor the surface properties. Finally, the review concludes with some future developments and perspectives related to forthcoming applications of LIPSS-based surfaces are discussed.

scholarly journals Wettability control of polymeric microstructures replicated from laser-patterned stamps

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Yangxi Fu ◽  
Marcos Soldera ◽  
Wei Wang ◽  
Stephan Milles ◽  
Kangfa Deng ◽  
...  
Keyword(s):  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Spatial Period ◽  
Structured Surfaces ◽  
High Adhesion ◽  
Direct Laser ◽  
Periodic Microstructures ◽  
Structure Height ◽  
Direct Laser Interference Patterning ◽  
Micropillar Arrays

AbstractIn this study, two-step approaches to fabricate periodic microstructures on polyethylene terephthalate (PET) and poly(methyl methacrylate) (PMMA) substrates are presented to control the wettability of polymeric surfaces. Micropillar arrays with periods between 1.6 and 4.6 µm are patterned by plate-to-plate hot embossing using chromium stamps structured by four-beam Direct Laser Interference Patterning (DLIP). By varying the laser parameters, the shape, spatial period, and structure height of the laser-induced topography on Cr stamps are controlled. After that, the wettability properties, namely the static, advancing/receding contact angles (CAs), and contact angle hysteresis were characterized on the patterned PET and PMMA surfaces. The results indicate that the micropillar arrays induced a hydrophobic state in both polymers with CAs up to 140° in the case of PET, without modifying the surface chemistry. However, the structured surfaces show high adhesion to water, as the droplets stick to the surfaces and do not roll down even upon turning the substrates upside down. To investigate the wetting state on the structured polymers, theoretical CAs predicted by Wenzel and Cassie-Baxter models for selected structured samples with different topographical characteristics are also calculated and compared with the experimental data.

scholarly journals Generation of Multiple Vector Optical Bottle Beams

Photonics ◽  
2021 ◽  
Vol 8 (6) ◽  
pp. 218
Author(s):  
Svetlana N. Khonina ◽  
Alexey P. Porfirev ◽  
Sergey G. Volotovskiy ◽  
Andrey V. Ustinov ◽  
Sergey A. Fomchenkov ◽  
...  
Keyword(s):  
Intensity Distribution ◽  
Polarization State ◽  
Spatial Dynamics ◽  
Surface Structures ◽  
Optical Traps ◽  
Spatial Transformation ◽  
Optical Elements ◽  
Periodic Surface ◽  
Matter Interaction ◽  
Different Types

We propose binary diffractive optical elements, combining several axicons of different types (axis-symmetrical and spiral), for the generation of a 3D intensity distribution in the form of multiple vector optical ‘bottle’ beams, which can be tailored by a change in the polarization state of the illumination radiation. The spatial dynamics of the obtained intensity distribution with different polarization states (circular and cylindrical of various orders) were investigated in paraxial mode numerically and experimentally. The designed binary axicons were manufactured using the e-beam lithography technique. The proposed combinations of optical elements can be used for the generation of vector optical traps in the field of laser trapping and manipulation, as well as for performing the spatial transformation of the polarization state of laser radiation, which is crucial in the field of laser-matter interaction for the generation of special morphologies of laser-induced periodic surface structures.

A New Computationally Efficient Model for Tempering in Multi-Tracks Laser Hardening

2009 ◽  
Author(s):  
Alessandro Fortunato ◽  
Leonardo Orazi ◽  
Giovanni Tani
Keyword(s):  
Process Parameters ◽  
Laser Power ◽  
Laser Scanning ◽  
Original Model ◽  
Laser Hardening ◽  
Computationally Efficient ◽  
Laser Process ◽  
Treat All ◽  
Tempering Time ◽  
Experimental Comparisons

The bottleneck in laser hardening principally occurs when large surfaces have to be treated because this process situation leads to multi-tracks laser scanning in order to treat all the component surface. Unfortunately, multi-tracks laser trajectories generate an unwanted tempering effect that depends on the overlapping of two close trajectories. To reduce the softening effects, a simulator capable to optimize the process parameters such as laser power and speed, number and types of trajectories, could sensibly increase the applicability of the process. In this paper an original model for the tempering is presented. By introducing a tempering time factor for the martensitic transformation, the hardness reduction can be predicted according to any laser process parameters, material and geometry. Experimental comparisons will be presented to prove the accuracy of the model.

Hierarchical Nano/Micro-structured Surfaces with High Surface Area/Volume Ratios

2021 ◽  
pp. 1-36
Author(s):  
Ketki Lichade ◽  
Yizhou Jiang ◽  
Yayue Pan
Keyword(s):  
Surface Structure ◽  
Surface Area ◽  
Light Trapping ◽  
High Surface ◽  
High Surface Area ◽  
Three Dimensional ◽  
Structure Design ◽  
Surface Structures ◽  
Structured Surfaces ◽  
Design And Manufacture

Abstract Recently, many studies have investigated additive manufacturing of hierarchical surfaces with high surface area/volume (SA/V) ratios, and their performance has been characterized for applications in next-generation functional devices. Despite recent advances, it remains challenging to design and manufacture high SA/V ratio structures with desired functionalities. In this study, we established the complex correlations among the SA/V ratio, surface structure geometry, functionality, and manufacturability in the Two-Photon Polymerization (TPP) process. Inspired by numerous natural structures, we proposed a 3-level hierarchical structure design along with the mathematical modeling of the SA/V ratio. Geometric and manufacturing constraints were modeled to create well-defined three-dimensional hierarchically structured surfaces with a high accuracy. A process flowchart was developed to design the proposed surface structures to achieve the target functionality, SA/V ratio, and geometric accuracy. Surfaces with varied SA/V ratios and hierarchy levels were designed and printed. The wettability and antireflection properties of the fabricated surfaces were characterized. It was observed that the wetting and antireflection properties of the 3-level design could be easily tailored by adjusting the design parameter settings and hierarchy levels. Furthermore, the proposed surface structure could change a naturally-hydrophilic surface to near-superhydrophobic. Geometrical light trapping effects were enabled and the antireflection property could be significantly enhanced (>80% less reflection) by the proposed hierarchical surface structures. Experimental results implied the great potential of the proposed surface structures for various applications such as microfluidics, optics, energy, and interfaces.

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