Femtosecond Laser Surface Texturing Research Articles

Laser-induced protruded bioinspired texturing of Ti-6Al-4V for controlled wettability in biomedical application

Bioinspired protruded textures with variable surface morphology and characteristics are getting worldwide popularity due to their wider applications. Among them controlled wettability for different materials through bioinspired textures is very essential to reduce the adhesion, bacterial contamination and growth, and drug delivery application. Even, identification and efficient fabrication of favorable bioinspired protrusions with optimum parameters are comparatively complex from normal textures through any material processing methods due to their complex shapes, form accuracy and dimensions. Therefore, this work targets the fabrication of four different types of protruded bioinspired textures namely, fish scale, protruded square, protruded circular, Python scale (snake) textured surface on biomedical grade Ti-6Al-4V titanium alloy for controlling the wettability using femtosecond laser surface texturing (LST). The optimum process parameters for the machining of Ti-6Al-4V were set as a temporal width of 350 fs, output power of 5.5 W, wavelength of 1030 nm, scanning speed of 100 mm/s and pulse rate of 500 KHz and three repetitions for all the texture types. To examine the effect of texture type, perimeter of all the fabricated textures was kept constant. Further, effect of varying perimeters was also analyzed for perimeter ranges from 300 to 500 µm. Surface morphology and characteristics were also analyzed for the measurement of texture consistency, dimensions and composition which was also related to the wettability results examined by static contact angle of the sessile drop method. Wetting of fish scale texture is decreased with increasing perimeter whereas of all other textures, wettability is going to be improved significantly.

Tailoring Resin–Metal Adhesion by Femtosecond Laser Surface Texturing

Epoxy resin wettability and adhesion on metal surfaces are of interest to composite manufacturing processes in two aspects: while higher adhesion is desired for composite to metal part bonding, lower adhesion is expected for metal tools used in the composite fabrication process. Among several surface modification techniques to achieve such increased/decreased adhesion strengths, femtosecond laser micromachining is a sustainable and scalable technique. Therefore, this study aims to explore epoxy resin adhesion behavior against femtosecond laser micromachined aluminum surfaces as a function of different microscale topographies. The texture types include microscale hexagonal and cylindrical hole patterns with different solid/air surface fractions and comparatively smaller‐scale laser‐induced periodic surface structures. Based on polished metal contact angle results, desired texture geometries are selected in a range to theoretically favor or inhibit resin penetration into microcavities. Theoretical predictions are derived from the capillary effect and Gibb's energy difference. The adhesion strength of resin to metal is examined by tensile tests. All the laser‐textured surfaces show considerably increased adhesion strengths compared to polished surfaces. Scanning electron microscopy and laser profilometry analysis on failed surfaces confirm resin penetration into all textures. Nevertheless, hexagonal holes, which exhibit the highest microcavity volume, show potential for air trapping.

Enhanced nucleate boiling of Novec 649 on thin metal foils via laser-induced periodic surface structures

The low boiling temperature of dielectric fluids makes them suitable for satisfying the cooling requirements of advanced high-energy-density devices commonly found in microelectronics. However, the high wettability/wickability of such coolants significantly affects the boiling dynamics, opening new research questions on the crucial role played by micro- and nanostructures on the boiling surface. While different studies point out the importance of microscale grooves, pillars and cavities to promote nucleation and enhance boiling heat transfer coefficient (HTC) for water, the scientific data to support such observations for dielectric fluids is sparse. In this regard, the present work provides an experimental investigation of the nucleate boiling enhancement of Novec 649 on thin metallic stainless-steel foils with tailored, laser-induced periodic surface structures (LIPSS). Femtosecond laser surface texturing was utilized to produce LIPSS with a periodicity of approx. 720 nm, while selected samples additionally included microscale grooves with a depth of 19.6 µm and a width of 25 µm, overlapped with the LIPSS features (labelled as GLIPSS). During boiling performance evaluation, high-speed IR thermography was used to measure the transient temperature fields of the boiling surface. LIPSS samples exhibited a reduction in wall superheat at the onset of boiling from 28 K to about 16 K, resulting in an HTC enhancement of about +65 %. Analysis of IR data was performed through multiscale proper orthogonal decomposition (mPOD) and revealed that the HTC enhancement in the presence of LIPSS is related to a faster heat transfer dynamics (dominant frequency: +54 %) occurring at a smaller spatial scale (dominant mean active site diameter: −12.5 %) and larger spatial density (dominant mean active site density: +39 %). Furthermore, the results for GLIPSS samples revealed a weak impact of micro features to the boiling performance of Novec 649, implying that sub-microscale surface topography is crucial to promote boiling in applications using dielectrics.

Dry Friction Properties of Friction Subsets and Angle Related to Surface Texture of Cemented Carbide by Femtosecond Laser Surface Texturing

This paper investigated the use of laser surface texturing (LST) to improve the tribological properties of YG6X cemented carbide. Three different spaced groove textures were processed on the surface of the YG6X carbide samples using a femtosecond laser. Friction experiments and friction simulations were performed under two friction subsets and two friction directions. The testing results showed that when the area density was 46%, the texture surface was beneficial when sliding against Si3N4, but not beneficial in reducing the coefficient of friction when sliding against Ti6Al4V titanium alloy. At area densities of 23% and 15.3%, the texture surface was beneficial when sliding against Si3N4, but not beneficial when sliding against the Ti6Al4V titanium alloy. When selecting the friction direction at 45° to the area density of 15.3%, the texture surface was not beneficial when sliding against the Si3N4 and Ti6Al4V titanium alloy. Sliding with Si3N4, the higher the stress value, the more easily the material was destroyed, leading to an elevated coefficient of friction and wear area. Sliding with Ti6Al4V titanium alloy, the higher the stress value of Ti6Al4V titanium alloy, the more easily the Ti6Al4V titanium alloy wore and generated a large number of abrasive chips.

Role of the intensity profile in femtosecond laser surface texturing: An experimental study

Femtosecond Laser Induced Surface Structures evolve from ripples to spikes upon the increase of the energy dose Φ. Nevertheless, for a fixed Φ, several process parameters (pulse energy, repetition rate, average power, overlapping, etc.) play an important role in determining the resulting morphology. Here we show that the beam intensity profile Î as well has an important bearing on the structures morphology evolution. In the case of a Gaussian beam, Î has been modified by varying the beam size d. We observed that for a stationary beam, and for a Φ value, passing from d = 13 µm to d = 200 µm makes possible the transition from ripples to spikes. This transition is made energetically advantageous by using a Top Hat profile. Compared to a 200 µm wide Gaussian beam, a 62 µm wide Top Hat reduces by 10 the Φ required to yield a similar surface morphology (coexistence of spikes and micro-groves). Confirming these results over a large surface could further validate the shaping of Î as a key approach to both fully exploit the output power of state of the art, kW class, femtosecond laser whilst increasing the surface texturing throughput.

Femtosecond laser surface texturing of polypropylene copolymer for automotive paint applications

Over the past few decades, polymers have progressively replaced metals and metallic alloys in technological applications for which, for example, lightweight, cost-effectiveness, chemical resistance and flexibility for precision-machines components are needed. Furthermore, there is great attention in modifying polymeric surfaces through physical and/or chemical treatments. In this context, the aim of this study is the enhancement of polypropylene specific automotive applications by inducing changes into its surface morphologies. Laser surface texturing technique is of particular interest because of its ability in producing morphological and, consequently, physical and/or chemical modifications on polymer surface. A femtosecond Titanium:Sapphire laser source was employed in order to investigate any variation of surface properties due to the fine tuning of both laser pulse energy and focused laser beam distance from the sample target. The laser treated samples were studied by Scanning Electron Microscopy, μ-Raman spectroscopy and contact angle measurements. The morphological analysis showed that micrometric sized dimple- and groove-like structures were produced after laser irradiation, maintaining mostly unchanged the chemical features of polypropylene surface but changing its wetting properties. These findings have been successfully applied to activate polypropylene surfaces for subsequent painting processes in automotive industry demonstrating that the femtosecond laser surface treatment here studied is an alternative method to the commonly used flame treatments on automotive components improving the paint adhesion to the treated polypropylene surfaces.

Femtosecond laser surface texturing of diamond-like nanocomposite films to improve tribological properties in lubricated sliding

We report on femtosecond laser ablation and surface micropatterning (texturing) of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films), aimed to improve tribological properties of laser-patterned films under lubricated sliding conditions. Femtosecond laser system generating pulses of 320-fs duration at the wavelength 515 nm is applied. Femtosecond laser ablation of 2.7-μm-thick DLN films is studied to determine optimum irradiation parameters for laser surface texturing with the requirements of the minimal spot size, high ablation rate, surface quality and pattern depth less than the film thickness. Periodic microcrater patterns (with 10 μm diameter, 2.2 μm depth, and different area density of microcraters) have been fabricated on the DLN films over the areas of 6 mm × 10 mm size. Tribological tests of the original and laser-patterned DLN films are performed using a ball-on-flat tribometer under linear reciprocating sliding against 100Cr6 steel balls in the presence of oil lubrication (engine oils of low and high viscosity). The ball-on-flat investigations have demonstrated the reduced friction and wear properties of the laser-textured DLN films, depending on the area density of microcraters and lubrication conditions. The obtained results evidence that femtosecond laser surface texturing is an effective technique to improve lubricated sliding performance of the DLN coatings.

Investigation of the effects of femtosecond laser metal surface texturing on bonding of PA 6 to steel

Abstract This paper investigates the effects of femtosecond laser surface texturing on the interfacial bond strength of steel and a thermoplastic polymer PA 6 film. Ultimately the textures will be used for hybrids that are manufactured using a near-infrared (NIR) laser-assisted automated tape placement (ATP) process and carbon fibre / PA 6 composites, therefore the NIR absorptance of the textured metal substrate is also of interest. To identify the influence of different surface structures on the bonding strength, lap shear samples were manufactured with laser textures varying in pulse length, hatch distance and ablated depth and tested by ASTM D 3165. The surface structures were analysed with white light interferometry (WLI) and scanning electron microscopy (SEM). Additional optical measurements in the infrared radiation range of 900 nm to 1100 nm were executed with a spectrophotometer to evaluate the laser absorptance for the NIR automated tape placement process. The lap shear strength increased to the highest value of 31.9 MPa with a tooth shaped laser texture using a 275 fs laser pulse width, a hatch distance of 600 μm an ablated depth of 40 μm. Also the absorptance for this sample increased by approximately 13% to 73% compared to the unprocessed pickled steel.

Effect of scanning speed and tin content on the tribological behavior of femtosecond laser textured tin-bronze alloy

Femtosecond laser surface texturing of soft bearing materials such as tin bronze is of great interest to manufacturing community since it aims at protecting valuable steel components by reducing wear and friction. This paper examines the effect of scanning speed on femtosecond laser texture characteristics of tin bronze alloy containing 8% and 12% tin. The friction and wear behavior of microgrooves produced on tin bronze alloy were reported under lubricated conditions. Higher tin content and lower scanning speed led to higher depth and width of the grooves. The friction performance was improved by increasing the number of reciprocating cycles on tin bronze alloy containing 12% tin at higher normal load. Grooves formed at lower scanning speed exhibited lower wear rate at higher load and higher frequency because of improved lubrication conditions. However, wear performance of tin bronze alloy containing 8% tin was less than that of untextured samples. The morphology of worn surfaces indicated the trapping of wear debris and possibility of formation of oil film due to which the lower coefficient of friction was observed.

Influence of Femtosecond Laser Parameters and Environment on Surface Texture Characteristics of Metals and Non-Metals – State of the Art

Enhancing the surface functionality by ultrashort pulsed laser texturing has received the considerable attention from researchers in the past few decades. Femtosecond lasers are widely adopted since it provides high repeatability and reproducibility by minimizing the heat affected zone (HAZ) and other collateral damages to a great extent. The present paper reports some recent studies being made worldwide on femtosecond laser surface texturing of metals, ceramics, polymers, semiconductors, thinfilms and advanced nanocomposites. It presents the state of the art knowledge in femtosecond laser surface texturing and the potential of this technology to improve properties in terms of biological, tribological and wetting performance. Since the texture quality and functionality are enhanced by the proper selection of appropriate laser parameters and ambient conditions for individual application, reporting the influence of laser parameters on surface texture characteristics assume utmost importance.

Femtosecond laser surface texturing of 3D poly-ε-caprolactone matrices for bone tissue engineering applications

Fibrous 3D matrices were fabricated from poly-ϵ-caprolactone (PCL) by fused deposition modeling. Femtosecond laser irradiation was then used to demonstrate the possibility to affect the porosity of the 3D PCL fiber meshes. The surface characteristics were analyzed by scanning electron microscopy (SEM) and confocal microscopy. The interrelationship was examined between the laser processing parameters (number of pulses, pulse energy applied) and the response of the biomaterial. The formation was demonstrated of well-defined micropores, while the original fiber structure was retained. The study of cells cultivation on the laser-modified scaffolds showed good adhesion compared to a non-modified scaffold. The results obtained showed that femtosecond laser processing can be used as an alternative non-contact tool in enhancing the porosity of artificial constructs, thus influencing the cell adhesion into fibrous meshes.

Angle-dependent lubricated tribological properties of stainless steel by femtosecond laser surface texturing

Lubricated tribological properties of stainless steel were investigated by femtosecond laser surface texturing. Regular-arranged micro-grooved textures with different spacing and micro-groove inclination angles (between micro-groove path and sliding direction) were produced on AISI 304L steel surfaces by an 800nm femtosecond laser. The spacing of micro-groove was varied from 25 to 300μm, and the inclination angles of micro-groove were measured as 90° and 45°. The tribological properties of the smooth and textured surfaces with micro-grooves were investigated by reciprocating ball-on-flat tests against Al2O3 ceramic balls under starved oil lubricated conditions. Results showed that the spacing of micro-grooves significantly affected the tribological property. With the increase of micro-groove spacing, the average friction coefficients and wear rates of textured surfaces initially decreased then increased. The tribological performance also depended on the inclination angles of micro-grooves. Among the investigated patterns, the micro-grooves perpendicular to the sliding direction exhibited the lowest average friction coefficient and wear rate to a certain extent. Femtosecond laser-induced surface texturing may remarkably improve friction and wear properties if the micro-grooves were properly distributed.

Femtosecond laser surface texturing of titanium as a method to reduce the adhesion of Staphylococcus aureus and biofilm formation

The aim of the present work was to investigate the possibility of using femtosecond laser surface texturing as a method to reduce the colonization of Grade 2 Titanium alloy surfaces by Staphylococcus aureus and the subsequent formation of biofilm. The laser treatments were carried out with a Yb:KYW chirped-pulse-regenerative amplification laser system with a central wavelength of 1030nm and a pulse duration of 500fs. Two types of surface textures, consisting of laser-induced periodic surface structures (LIPSS) and nanopillars, were produced. The topography, chemical composition and phase constitution of these surfaces were investigated by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, micro-Raman spectroscopy, and X-ray diffraction. Surface wettability was assessed by the sessile drop method using water and diiodomethane as testing liquids. The response of S. aureus put into contact with the laser treated surfaces in controlled conditions was investigated by epifluorescence microscopy and scanning electron microscopy 48h after cell seeding. The results achieved show that the laser treatment reduces significantly the bacterial adhesion to the surface as well as biofilm formation as compared to a reference polished surfaces and suggest that femtosecond laser texturing is a simple and promising method for endowing dental and orthopedic titanium implants with antibacterial properties, reducing the risk of implant-associated infections without requiring immobilized antibacterial substances, nanoparticles or coatings.

Tribological behavior of femtosecond laser textured surfaces of 20CrNiMo/beryllium bronze tribo-pairs

Purpose – This paper aims to carry out tribological experiments to explore the applications of femtosecond laser surface texturing technology on rock bit sliding bearing to enhance the lifetime and working performance of rock bit sliding bearing under high temperature and heavy load conditions. Design/methodology/approach – Surface textures on beryllium bronze specimen were fabricated by femtosecond laser ablation (800 nm wavelength, 40 fs pulse duration, 1 kHz pulse repetition frequency), and then the tribological behaviors of pin-on-disc configuration of rock bit bearing were performed with 20CrNiMo/beryllium bronze tribo-pairs under non-Newtonian lubrication of rock bit grease. Findings – The results showed that the surface texture on beryllium bronze specimens with specific geometrical features can be achieved by optimizing femtosecond laser processing via adjusting laser peak power and exposure time; more than 52 per cent of friction reduction was obtained from surface texture with a depth-to-diameter ratio of 0.165 and area ratio of 5 per cent at a shear rate of 1301 s−1 under the heavy load of 20 MPa and high temperature of 120°C, and the lubrication regime of rock bit bearing unit tribo-pairs was improved from boundary to mixed lubrication, which indicated that femtosecond laser ablation technique showed great potential in promoting service life and working performance of rock bit bearing. Originality/value – Femtosecond laser-irradiated surface texture has the potential possibility for application in rock bit sliding bearing to improve the lubrication performance. Because proper micro dimples showed good lubrication and wear resistance performance for unit tribo-pairs of rock bit sliding bearing under high temperature, heavy load and non-Newtonian lubrication conditions, which is very important to improve the efficiency of breaking rock and accelerate the development of deep-water oil and gas resources.

Blackening of magnesium alloy using femtosecond laser.

Magnesium alloy, a potential structural and biodegradable material, has been increasingly attracting attention. In this paper, two structures with enhanced light absorption on an AZ31B magnesium surface are fabricated by femtosecond laser texturing. Laser power and the number of laser pulses are mainly investigated for darkening effect. After irradiation, surface characteristics are analyzed by a scanning electron microscope equipped with an energy dispersive spectrometer and laser scanning confocal microscope. The darkening effect is investigated by a spectrophotometer with an integrating sphere. Microgroove and stripe structures are obtained, which are covered with homogeneous nanoprotrusions and nanoparticles. The main surface chemical composition after laser ablation is MgO. The optimal light absorption in the visible range (wavelength of 400-800nm) reaches about 98%, which is significantly improved compared with the untreated surface. The enhanced light absorption is mainly attributed to surface structure. Femtosecond laser surface texturing technology offers potential in the application of stealth technology, airborne devices, and biomedicine.

Modulation of dry tribological property of stainless steel by femtosecond laser surface texturing

We reported on the modification of tribological properties of stainless steel by femtosecond laser surface microstructuring. Regular arranged micro-grooved textures with different spacing were produced on the AISI 304L steel surfaces by an 800-nm femtosecond laser. The tribological properties of smooth surface and textured surface were investigated by carrying out reciprocating ball-on-flat tests against Al2O3 ceramic balls under dry friction. Results show that the spacing of micro-grooves had a significant impact on friction coefficient of textured surfaces. Furthermore, the wear behaviors of smooth and textured surface were also investigated. Femtosecond laser surface texturing had a marked potential for modulating friction and wear properties if the micro-grooves were distributed in an appropriate manner.

Femtosecond laser surface structuring technique for making human enamel and dentin surfaces superwetting

It is known that good wettability of enamel and dentin surfaces is a key factor in enhancing adhesion of restorative materials in dentistry. Here, we report on a femtosecond laser surface texturing approach that makes both the enamel and dentine surfaces superwetting. In contrast to the traditional chemical etching that yields random surface structures, this new approach produces engineered surface structures. The surface structure engineered and tested here is an array of femtosecond laser-produced parallel microgrooves that generates a strong capillary force. Due to the powerful capillary action, water is rapidly sucked into this engineered surface structure and spreads even on a vertical surface.

Making human enamel and dentin surfaces superwetting for enhanced adhesion

Good wettability of enamel and dentin surfaces is an important factor in enhancing adhesion of restorative materials in dentistry. In this study, we developed a femtosecond laser surface texturing approach that makes both the enamel and dentine surfaces superwetting. In contrast to the traditional chemical etching that yields random surface structures, this approach produces engineered surface structures. The surface structure engineered and tested here is an array of parallel microgrooves that generates a strong capillary force. Due to the powerful capillary action, water is rapidly sucked into this engineered surface structure and spreads even on a vertical surface.

Femtosecond laser surface texturing of a nickel-based superalloy

Femtosecond laser (180 fs, 775 nm, 1 kHz) surface modification of the nickel-based superalloy C263 is investigated. The laser beam was scanned onto areas on the substrate with macroscopic dimensions using different fluences ( F = 0.28–30 J/cm 2), speeds ( υ = 1–10 mm/s) and number of overscans (5–90). The evolution of surface morphology, roughness, ablation depth and volume ablation rate with laser micromachining parameters were determined. The surface morphology is characterized by ripples for low average powers while for high average powers the surface becomes porous.