Laser-treated Samples Research Articles

Wetting angle stability of steel surface structures after laser treatment

In this work, we have used a nanosecond pulsed fiber laser to modify the wettability characteristics of AISI 430 steel. For this, various surface morphologies were created on the samples by laser irradiation with different overlapping and intensity parameters. Immediately upon laser treatment, all the structured samples acquired either hydrophilic or superhydrophilic wetting angles. All the samples were also analyzed with XRD. Then, laser-treated samples were kept in ambient air and/or low-temperature annealing was applied to reach hydrophobic surface properties. Interestingly, these surfaces returned back practically to their initial wetting state by cleaning in an ultrasonic bath. The obtained results are analyzed based on the existing wettability models.

The In-Depth Studies of Pulsed UV Laser-Modified TiO2 Nanotubes: The Influence of Geometry, Crystallinity, and Processing Parameters

The laser processing of the titania nanotubes has been investigated in terms of morphology, structure, and optical properties of the obtained material. The length of the nanotubes and crystallinity, as well as the atmosphere of the laser treatment, were taken into account. The degree of changes of the initial geometry of nanotubes were checked by means of scanning electron microscopy, which visualizes both the surface and the cross-section. The phase conversion from the amorphous to anatase has been achieved for laser-treated amorphous material, whereas modification of calcined one led to distortion within the crystal structure. This result is confirmed both by Raman and grazing incident XRD measurements. The latter studies provided an in-depth analysis of the crystalline arrangement and allowed also for determining the propagation of laser modification. The narrowing of the optical bandgap for laser-treated samples has been observed. Laser treatment of TiO2 nanotubes can lead to the preparation of the material of desired structural and optical parameters. The usage of the motorized table during processing enables induction of changes in the precisely selected area of the sample within a very short time.

Microstructure and microhardness of a novel TiZrAlV alloy by laser gas nitriding at different laser powers

The Ti–20Zr–6.5Al–4V (T20Z, wt%) alloy surface was treated by the process of laser surface nitriding. The evolution of microstructures and microhardness has been investigated by changing the laser power parameter from 120 to 240 W. All laser-treated T20Z samples show two regions with distinctly different microstructural features, as compared with the untreated substrate: dense TiN dendrites and (α + β) − Ti (remelting zone, RMZ), nanoscale α laths doped with part of β phase (heat-affected zone, HAZ). The formation of TiN dendrites can be analyzed by a series of complex reactions during the process of melting and solidification. The increase in laser power results in the increase in content of TiN dendrite which is mainly due to the increase in energy input. In HAZ, the self-quenching effect leads to the formation of nanoscale α laths and the residue of β phase. Microhardness profile of different regions was measured from the surface to the interior, and the highest microhardness was obtained (~ HV 916.8) in the RMZ, as the laser power was set to 240 W. In the present study, we explained various microstructural characteristics induced by laser surface nitriding treatment.

A new approach to synthesis Ti2AlC MAX phase using PVD coating and post-laser treatment

The Ti2AlC MAX phase was synthesized on the Ti-6Al-4V alloy substrate using a novel technique. In contrary to the most techniques used for synthesizing the MAX phases in which the metal powders were the main raw material, the metal powder wasn't used in this procedure. The Ti-6Al-4V plates were carbon coated by physical vapor deposition (PVD), and then the Nd: YAG and diode lasers were irradiated on the coated samples. The laser process was performed at different variables including the power, scan speed, and focal position of the laser. The laser-treated samples were investigated by optical microscopy, X-Ray diffraction (XRD), and field-emission scanning electron microscopy (FESEM) equipped with energy disperse spectroscopy (EDS). In addition to the other phases such as titanium carbide (TiC) and titanium nitride (TiN), the Ti2AlC MAX phase was also detected by the XRD analysis. The hardness of the coated irradiated samples was nearly 2.5 to 4.5 times higher than the substrate. The wear and friction performances of the samples was evaluated using a reciprocal wear device in which the AISI 52100 steel with the hardness of 63 HRC was used as the counterpart. The wear rate of the laser-treated sample decreased about 81% with respect to the Ti-6Al-4V substrate. The average friction coefficient reduced nearly 66% after the laser treating of the Ti-6Al-4V sample. The SEM images of the worn surfaces and debris were used to deduce the wear mechanisms. The abrasive wear was the dominant wear mechanism.

Scalable Route toward Superior Photoresponse of UV-Laser-Treated TiO2 Nanotubes.

Titanium dioxide nanotubes gain considerable attention as a photoactive material due to chemical stability, photocorrosion resistance, or low-cost manufacturing method. This work presents scalable pulsed laser modification of TiO2 nanotubes resulting in enhanced photoactivity in a system equipped with a motorized table, which allows for modifications of both precisely selected and any-large sample area. Images obtained from scanning electron microscopy along with Raman and UV-vis spectra of laser-treated samples in a good agreement indicate the presence of additional laser-induced shallow states within band gap via degradation of crystalline structure. However, X-ray photoelectron spectroscopy spectra revealed no change of chemical nature of the modified sample surface. Photoelectrochemical measurements demonstrate superior photoresponse of laser-treated samples up to 1.45-fold for an energy beam fluence of 40 mJ/cm2 compared to that of calcined one. According to the obtained results, optimal processing parameters were captured. Mott-Schottky analysis obtained from impedance measurements indicates an enormous (over an order of magnitude) increase of donor density along with a +0.74 V positive shift of flat band potential. Such changes in electronic structure are most likely responsible for enhanced photoactivity. Thus, the elaborated method of laser nanostructuring can be successfully employed to the large-scale modification of titania nanotubes resulting in their superior photoactivity. According to that, the results of our work provide a contribution to wider applications of materials based on titania nanotubes.

Acid resistance enhancement of human tooth enamel surface by Nd:YAG laser and incorporating silver nanoparticles: in vitro study

This work was devoted to assess the use of Nd:YAG laser with and without nanosilver particles to enhance tooth resistance of dental enamel against carries. Forty-eight tooth samples were randomly divided into three main groups and received different treatments. Samples of group 1 were illuminated by a single pulse at different laser fluences, while those of group 2 received different number of laser pulses at fixed laser fluence, and finally the samples of group 3 received laser and colloidal silver nanoparticle treatments at different conditions. The samples were subjected to Vickers microhardness test, atomic force microscopy analysis, scanning electron microscopy observation, energy dispersive spectroscopy investigation, and demineralization and re-mineralization tests. Due to fast laser heating and quenching, a significant microhardness increase in the treated dental enamel samples was seen. This resulted in an improvement in the enamel resistance against acids because of the decrease in hydroxyapatite lattice stress and the reduction in enamel solubility. The addition of silver nanoparticles to the laser-treated enamel surface helped stabilize the granules of the enamel surface tissue under the effect of laser irradiation. The demineralization of laser-treated samples showed higher Ca/P ratios than control group, indicating a higher resistance against acids. The combined laser illumination and the addition of silver nanoparticles lowered the tooth abrasion degree and increased tooth resistance to decay. The demineralized samples of all laser-treated samples had higher Ca/P ratios compared to the demineralized control sample. Laser energy has modified the Ca/P mineral ratio and forms steadier and lesser acid soluble compositions.

Laser surface modifications of Fe-14Cr ferritic alloy for improved corrosion performance

Laser processing parameters of an ytterbium fiber laser were explored using a two-stage searching strategy to form an optimum surface layer on Fe-14Cr ferritic alloy samples for improved corrosion performance. With one or two passes of laser surface scanning, corrosion behavior and surface layer uniformity were investigated for different laser parameters utilizing energy-dispersive X-ray spectroscopy (EDS) and electrochemical tests in saltwater. The optimum laser processing parameters were found to be 175 w of laser power, 200 mm/s of scanning speed, and 0.025 mm of hatching space. Corrosion behavior of laser-treated samples with the optimum laser parameters was found to be 5 and 13 times better respectively than the baseline sample in 3.5 wt% NaCl water solution, in term of corrosion rate. The formation of a uniform thin oxidation layer was the main reason for the improved corrosion performance.

Mechanical Properties of Laser Shock-Peened Regions of SS316LN and SS304 Studied by Nanoindentation

Nanoindentation has been used to evaluate various mechanical properties of affected regions of laser shock-peened (LSP) stainless steels, SS316LN and SS304 plates. Depending on the applied laser parameters (laser energy, pulse width), the hardness was varied in the range 3.5–6.2 GPa in comparison with the untreated sample hardness of 2.93 GPa for SS316LN. Similarly in SS304, the hardness has been improved to 5.73 GPa in comparison with the untreated specimen hardness of 2.57 GPa. The improvement in the hardness for the laser-treated stainless steel targets is attributed to various factors viz., increment in internal frictional stress, dislocation–dislocation interaction and solute–dislocation interactions. Effect of laser energy is not appeared in the hardness values but a difference in hardness values with the pulse width has been observed. The deformation characteristics such as strain rate sensitivity and activation volume were evaluated from the indentation creep data. Notable change in the strain rate sensitivity is not observed for the laser-treated samples in comparison with the untreated samples and the range of values measured between 0.01 and 0.02. The activation volumes for both the treated and untreated samples were in the range, 100–200 b3. There was a slight decrease in activation volume in the laser-treated samples. Several rate-controlling deformation mechanisms appear to be operative in these treated samples, in addition to the dislocation-based mechanisms.

Effect of laser wavelength on the thermal behavior of amorphous GST films irradiated by a single frequency-tripled picosecond laser

In this paper, the effect of laser wavelength on the thermal behavior of amorphous Ge2Sb2Te5 (a-GST) films induced by a frequency-tripled picosecond laser was carried out using 3D surface profile, SEM, TEM and Raman measurement. Melting thresholds of a-GST films with different wavelengths of 355 nm (3.5 mJ/cm2), 532 nm (28 mJ/cm2) and 1064 nm (22.3 mJ/cm2) were obtained, respectively. It showed that with the increase of wavelength from 355 to 532 and 1064 nm, pit morphologies and crystallization degree didn’t follow a monotonous relation, which were mainly affected by melting threshold, optical penetration depth as well as photon energy. TEM images demonstrated that 532 nm laser-treated samples got more complete crystallization than those 355 nm laser treated. Besides, for the remarkable discrepancy in optical penetration depth among the three laser wavelengths, the crystallization process of a-GST at 355 and 532 nm wavelengths performed with a surficial heating mode, different from that at 1064 nm wavelength with a body heating mode. The present study paves the way to achieve the big-data storage using different wavelengths.

Optimization of biocompatibility in a laser surface treated Mg-AZ31B alloy.

Biodegradable bone implants can remove the need for subsequent bone-implant surgeries by controlled biomineralization and degradation. Although Mg-alloys generally possess biocompatible properties, they corrode rapidly, thereby preventing sufficient hydroxyapatite formation and biomineral growth. In an attempt to address these limitations, laser surface treatments were performed via the employment of a continuous wave Nd:YAG laser on the Mg-AZ31B alloy using laser fluences in the range of 1.06-4.24 J/mm2 (250-1000 W). The laser-treated samples were investigated for their wettability in simulated body fluid. In vitro analyses were performed in simulated body fluid to examine corrosion and biomineralization behavior on the laser-treated samples. Statistical optimization algorithms based on wettability data predicted an optimal laser fluence of 3.286J/mm2 (775 W) within the range of laser fluences used in the present study for achieving a balance between biodegradation and biomineralization. Confirmatory tests on optimized samples indicated an up to 84% grain size reduction in laser-treated surface regions, a several-fold increase in Mg17Al12 (β) phase volume fraction, a reasonably abundant formation of hydroxyapatite, and increased rates of biomineralization that exceeded degradation. These findings indicate the potential of laser surface engineering to realize Mg-AZ31B alloy as a viable biodegradable bone implant material.

Microstructural and Mechanical Properties Examination of High-Power Diode Laser-Treated R260 Grade Rail Steels Under Different Processing Temperatures

In the present study, high-power diode laser surface treatment was implemented to R260 grade steel with three different processing temperatures (1100 °C, 1200 °C, and 1300 °C) at the laser power of 1750 W and scanning speed of 6 mm/s, in order to identify the effect of various processing temperatures on the mechanical performance. According to the test results, the laser-treated sample at 1300 °C showed much better mechanical performance among the other laser-treated samples. It was found that the laser-treated sample at 1300 °C had about 3 times more surface hardness, a 43 pct increase in yield strength, and a 53 pct increase in toughness value compared to the untreated sample. Microstructural investigations showed that this surface treatment did not only generate a martensitic structure with a certain depth but also provided the formation of a fine pearlitic structure contributing to an increase in the mechanical properties. As a conclusion, it was found that the processing temperature is one of the critical factors affecting the mechanical properties in the laser hardening process. Moreover, the results demonstrated that this treatment method might be an alternative method to enhance the mechanical properties of existing rail steels online without the need for rail disassembly, reducing operational costs.

Surface micro-structuring of type 304 stainless steel by femtosecond pulsed laser: effect on surface wettability and corrosion resistance

This paper presents results on femtosecond (fs) pulsed laser-based surface micro-structuring of type 304 stainless steel (304 SS). Post laser treatment surface wettability and corrosion resistance investigation are reported. SS sample surfaces have been micro-structured using a typical laser fluence of ~ 0.9 J/cm2 for varying sample scanning speed in the range 25–1000 µm/s. Dense array of micro-protrusions have been generated without formation of a crater for an optimized target scan speed exceeding 200 µm/s. Static water contact angle (WCA) measurement indicated super-hydrophilic behavior immediately after laser treatment. However, hydrophilicity (wettability) was found to decrease with storage time with sample becoming highly hydrophobic (WCA: 144° ± 5°) within 50 days after laser treatment. Corrosion resistance of the laser-treated samples was measured by potentio-dynamic polarization technique. Fs laser micro-structured SS has shown poorer corrosion resistance in comparison to pristine surface. Observed poorer corrosion resistance of laser-treated surface has been explained on the basis of surface chemical composition and surface roughness. The results demonstrated that corrosion resistance increased with increasing hydrophobicity of the SS surface.

In vitro bioactivity and biocompatibility of femtosecond laser-modified Ti6Al4V alloy

The present work investigates bioactivity and biocompatibility of femtosecond (fs) laser surface-modified Ti6Al4V alloy (Ti-alloy). Self-aligned conical surface features were generated on Ti-alloy when laser irradiated employing a Ti:sapphire pulsed fs laser of wavelength 800 nm. Modification of surface chemical composition resulting from fs-laser irradiation of Ti-alloy was examined using Grazing incidence X-ray diffraction (GIXRD) technique and micro-Raman spectroscopy. Sub-oxide phase of titanium was detected on Ti-alloy surface post-fs-laser irradiation leading to increased oxygen vacancies on sample surface. For in vitro bioactivity tests, untreated and fs-laser-treated samples were immersed in simulated body fluid for 2 weeks. Evidence of hydroxyapatite deposition on both untreated Ti-alloy, as well as, fs-laser-treated Ti-alloy surfaces after in vitro tests were provided by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), GIXRD, Fourier transform infrared spectroscopy (FTIR), and micro-Raman spectroscopy. Superior growth of HAP was observed on fs-laser-modified Ti-alloy surface in comparison with untreated surface. Biocompatibility of the laser-treated Ti-alloy was investigated by studying anchoring and growth of human osteosarcoma cell line (U2OS) on it. Using MTT assay technique in vitro cell viability and growth potential in the presence of untreated and laser-treated Ti-alloy samples were assessed. MTT test results demonstrated that, neither cell viability, nor growth were affected in the presence of either the untreated or laser-treated sample surfaces. In addition, in comparison with the untreated Ti-alloy surface, the fs-laser-treated Ti-alloy surface showed more efficient cellular attachment when examined under confocal microscope.

In-Depth Study of Laser Diode Ablation of Kapton Polyimide for Flexible Conductive Substrates.

This work presents a detailed study of the photothermal ablation of Kapton® polyimide by a laser diode targeting its electrical conductivity enhancement. Laser-treated samples were structurally characterized using Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), as well as Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy. The results show that the laser-assisted ablation constitutes a simple one-step and environmental friendly method to induce graphene-derived structures on the surface of polyimide films. The laser-modified surface was also electrically characterized through the Transmission Line Method (TLM) aiming at the improvement of the conductivity of the samples by tuning the laser power and the extraction of the contact resistance of the electrodes. Once the laser-ablation process is optimized, the samples increase their conductivity up to six orders of magnitude, being comparable to that of graphene obtained by chemical vapor deposition or by the reduction of graphene-oxide. Additionally, we show that the contact resistance can be decreased down to promising values of ∼2 when using silver-based electrodes.

Corrosion Inhibition of Cold-rolled Low Carbon Steel with Pulse Fiber Laser Ablation in Water

This study aims at the use of a fiber laser for modifying the surface properties of cold-rolled low carbon steel via a pulse laser ablation technique in water. The effect on the corrosion behavior of the fiber laser-treated metal surface was investigated in NaCl and HCl environments. Electrochemical tests showed significant improvement in the corrosion resistance of the laser-treated sample in NaCl, with an increase in open-circuit potential (OCP) from − 0.65 to − 0.60 V and an inhibition efficiency of 89.22% as obtained from the impedance study. Such improvement was less significant in an acidic environment. Lower corrosion rates of 20.9 mpy and 5.819 × 103 mpy were obtained for the laser-treated samples in neutral and acidic electrolytes, respectively, than the corrosion rates obtained for the as-received samples (33.2 mpy and 11.98 × 103 mpy). Morphological analysis indicated a passive film built by spherical grains of regular size on the metal surface after laser treatment. The corrosion inhibition effects in NaCl were evident by the nonexistence of the common corrosion products of lepidocrocite and crystalline structures that were seen on as-received samples; only polyhedral crystals with micrograins grown on them were seen covering the laser-treated surface. Therefore, the laser treatment using a fiber laser source improved the corrosion resistance of cold-rolled low carbon steel.

Properties of Al- and Ga-doped thin zinc oxide films treated with UV laser radiation

This paper reports the Nd:YAG laser irradiation treated modified properties of aluminum (Al) and gallium (Ga) co-doped zinc oxide (ZnO) (AGZO) films prepared on Si-substrate via combined sol–gel and spin-coating method. The impact of varying laser energy (150–200 mJ) on the structure, morphology, electrical and optical properties of such AGZO films were determined. Laser-treated samples were characterized using various analytical tools. Present techniques could achieve a high-quality polycrystalline films compared with those produced via conventional high temperature processing. AGZO films irradiated with third harmonics UV radiation (355 nm) from Nd:YAG laser source revealed very low resistivity of 4.02 × 10− 3 Ω cm. The structural properties grain size was calculated firm the X-ray diffraction spectra using the Scherrer equation that increased from 12.7 to 22.5 nm as the annealing laser energy increased from (150–200) mJ. The differences in crystallinity and orientation are explained in terms of the thermal effect caused by laser irradiation. (FESEM) images have been demonstrated that Nd:YAG laser annealing can significantly improve the crystallinity level, densification, and surface flatness of sol–gel derived AGZO thin films that occurred as a result of laser processing. Synthesized AGZO films displayed favorable growth orientation along (101) lattice direction. AGZO films with energy band gap of 3.37–3.41 eV were obtained. Results on the crystallinity, surface morphology, roughness, bonding vibration, absorption, photoluminescence, and resistivity of the laser-irradiated films were analyzed and discussed.

The variation in surface morphology and hardness of human deciduous teeth samples after laser irradiation

The variation in surface morphology and hardness of human deciduous teeth samples has been investigated after laser irradiation at different wavelengths and energies. Nd:YAG was employed as a source of irradiation for IR (1064 nm) and visible (532 nm) radiation, whereas an excimer laser was used as the source of UV (248 nm) radiation. Scanning electron microscope (SEM) analysis was carried out to reveal the surface morphological evolution of teeth samples. Vickers microhardness tester was employed to investigate the modifications in the hardness of the laser-treated samples. It is observed from SEM analysis that IR wavelength is responsible for ablation of collagen matrix and intertubular dentine. For visible radiation, the ablation of collagen along with hydroxypatite is observed. With UV radiation, the ablation of peritubular dentine is dominant and is responsible for the sealing of tubules. The decrease in hardness at lower energy for both wavelengths is due to the evaporation of carbon content. With increasing energy, evaporation of water along with carbon content, and resolidification and re-organization of inorganic content causes the increase in hardness of the treated dentine. SEM as well as microhardness analyses reveal that laser wavelengths and energy of laser radiation significantly influence the surface morphology and hardness of samples.

Serendipitous vs. systematic search for room-temperature superconductivity

This article summarizes the results from a decade of research which began following a serendipitous discovery and continued with a systematic, Edisonian approach. During the serendipitous stage, there were indications of very-high- $$T_\mathrm{c}$$ superconductivity (at about 200–250 K) detected in laser-treated samples of doped strontium ruthenates. The synthesis route that had been used was strongly out of equilibrium. In spite of our intense studies, later, synthetic efforts along a route closer to equilibrium conditions did not reveal high- $$T_\mathrm{c}$$ superconductivity in the new samples, though there were indications of low- $$T_\mathrm{c}$$ superconductivity. Before the arrival of results on nonequilibrium synthetic routes, it is an appropriate time to summarize the results found within the equilibrium routes, analyze potential corollaries of the complex structure of samples within our initial findings, and discuss the next steps of research.

Mammalian fibroblast cells show strong preference for laser-generated hybrid amorphous silicon-SiO2 textures.

In this study, we investigated a method to produce bioactive hybrid amorphous silicon and silicon oxide patterns using nanosecond laser pulses. Microscale line patterns were made by laser pulses on silicon wafers at different frequencies (25, 70 and 100 kHz), resulting in ablation patterns with frequency-dependent physical and chemical properties. Incubating the laser-treated silicon substrates with simulated body fluid demonstrated that the physicochemical properties of the laser-treated samples were stable under these conditions, and favored the deposition of bone-like apatite. More importantly, while NIH 3T3 fibroblasts did colonize the untreated regions of the silicon wafers, they showed a strong preference for the laser-treated regions, and further discriminated between substrates treated with different frequencies. Taken together, these data suggest that laser materials processing of silicon-based devices is a promising avenue to pursue in the production of biosensors and other bionic devices.

The Alumina Film Nanomorphology Formed to Improve the Corrosion Resistance of Al-2.0 wt% Fe Alloy as Result of the Laser Surface Melting Technique Applied

The laser surface remelting (LSR) treatment was performed to Al-2.0 wt% Fe alloy with a 2 kW Yb-fiber laser (IPG YLR-2000S). The substrate and laser-treated material characterization were executed using different techniques. Among them, the microstructure was analyzed by optical microscope, SEM, low-angle X-ray diffraction (LAXRD) and the corrosion test was made in aerated solution of 0.1 M H2SO4 at a temperature of 25°C ± 0.5°C. As result was shown, the micrograph of LSR-treated material displaying can be a fine cellular structure and the existence of certain nano-porosities and a similar to a nano-dendritic growth was observed too. The characteristic of melted zone was constituted of metastable phases according to the result of x-rays and the behavior corrosion as a result of the LSR-treated sample, which it was shown to be more resistant to corrosion than the untreated sample. A comparative study was carried out of the cyclic polarization of the laser-treated and untreated samples, demonstrating that the reduction and oxidation reverse peaks were not observed and being the cyclic polarization behavior was of irreversible character in both samples, however, the LSR-treated sample propitious the passivity on the surface also reduced the corrosion phenomena. Wherefore, this type of laser-treated alloy can be applied in the aerospace, aeronautic and automobilist industries.