Laser-induced Oxidation Research Articles

Study on Laser-Induced Oxidation of Ti6Al4V Alloy Under Two Different Reactive Atmospheres

Abstract The oxidation behavior of Ti6Al4V titanium alloy under laser irradiation in atmospheric and oxygen-assisted conditions was studied. A nanosecond-pulsed Yb: glass fiber laser was used. The thickness of oxide layer, microstructure, and phase composition of the material after laser irradiation were investigated. The characterization of the surface and subsurface microstructure, as well as the cross-sectional morphology were performed using scanning electron microscopy (SEM). The phase identification was performed using X-ray diffraction (XRD). The combined effects of accumulated laser fluence and reactive atmosphere on the oxidation behavior of Ti6Al4V were also studied in detail. With an increase in accumulated laser fluence, a porous and easily removable oxide layer gradually formed on the surface, whereas a compact oxide layer was also formed. At high accumulated laser fluence, the thickness of the porous oxide layer increased dramatically, while the change of thickness of compact oxide layer was not obvious. The reactive atmosphere also had a significant influence on the microstructure of the surface and subsurface layers. SEM and XRD results revealed existence of strong oxidation reactions that underwent in the condition of assisted oxygen delivery at a fixed accumulated laser fluence. The oxide layer was composed mainly of anatase and rutile titanium oxides.

Study on laser-induced oxidation modification coupled with micro milling of WC-Co cemented carbide

Cemented carbide is known as “industrial tooth” and has wide applications in terms of military, aerospace and other fields. In this study, a compound processing approach named laser-induced oxidation modification coupled with micro milling (LCMM) is proposed to solve its poor micro machining performance. The oxidation mechanism of WC-Co cemented carbide is revealed. Surface morphology and cross-section of WC-Co cemented carbide are investigated after laser irradiation under various average laser power and two reaction environment. Research results present that at the average power of 5 W, scanning speed of 0.5 mm/s and oxygen-rich oxygen condition, the laser-induced oxidation process is optimal. The thickness of oxide layer and sub-layer is 9.1 μm and 2.7 μm, and the material surface generates porous and loose oxide layer. In addition, comparative analyses are performed and discussed in detail considering milling force, tool wear and surface quality of machined micro slot. In comparison with conventional micro milling (CONM), cutting force of Fx and thrust force of Fy generated in removing the oxide layer in LCMM are reduced by 56% and 58% to maximum extent, respectively. The machined surface quality in LCMM is better than that in CONM with a slower rate of increase in surface roughness (Sa). At ap = 2 μm and fz = 1.5 μm/z, surface quality of machined micro slot in LCMM is superior to that at other milling parameters, and the surface roughness reach 57 nm. Tool wear rate in LCMM is greatly improved and tool wear mechanism mainly includes slight adhesion wear and abrasion wear. While, in CONM the wear mechanisms are severe abrasion wear, chipping and adhesion wear. The tool service life in LCMM can be promoted more than double.

Laser-Assisted Surface Texturing of Ti/Zr Multilayers for Mesenchymal Stem Cell Response

The formation of an ordered surface texture with micro and nanometer features on Ti/Zr multilayers is studied for better understanding and improvement of cell integration. Nanocomposite in form 30×(Ti/Zr)/Si thin films was deposited by ion sputtering on Si substrate for biocompatibility investigation. Surface texturing by femtosecond laser processing made it possible to form the laser-induced periodic surface structure (LIPSS) in each laser-written line. At fluence slightly above the ablation threshold, beside the formation of low spatial frequency-LIPSS (LSFL) oriented perpendicular to the direction of the laser polarization, the laser-induced surface oxidation was achieved on the irradiated area. Intermixing between the Ti and Zr layers with the formation of alloy in the sub-surface region was attained during the laser processing. The surface of the Ti/Zr multilayer system with changed composition and topography was used to observe the effect of topography on the survival, adhesion and proliferation of the murine mesenchymal stem cells (MSCs). Confocal and SEM microscopy images showed that cell adhesion and their growth improve on these modified surfaces, with tendency of the cell orientation along of LIPSS in laser-written lines.

Effect of thermal oxidation on detection of adulteration at low concentrations in extra virgin olive oil: Study based on laser-induced fluorescence spectroscopy combined with KPCA–LDA

The fluorescence spectra of oil samples were obtained by laser-induced fluorescence spectroscopy and thermal oxidation stoichiometry at room temperature and 80 °C respectively. The Support Vector Machine, combined with Principal Component Analysis-Linear Discriminant Analysis (PCA-LDA), could distinguish pure extra virgin olive oils (EVOO) from oils adulterated with 2% soybean oil, with a recognition rate of 100%. Besides, as the intensity of the fluorescence spectra and concentration of the adulterants showed a non-linear relationship, linear dimension reduction methods may lead to overlapping of the different adulterated concentrations features, resulting in large errors in quantifying adulteration. In this paper, Kernel Principal Component Analysis-Linear Discriminant Analysis (KPCA-LDA) was applied instead of PCA-LDA to extract fluorescence spectra features, and a Partial Least Squares Regression model was established, which could quantify adulterants such as low percentages of soybean oil in EVOO. The coefficient of determination and root mean squared error were 0.92 and 2.72%, respectively.

Physical similarity of the processes of laser thermochemical recording on thin metal films and modeling the recording of submicron structures

Laser thermochemical recording is a flexible method for direct writing the binary planar structures (for instance, diffractive optical elements) by a local laser-induced oxidation of thin metal films. Unfortunately, due to excess of influencing parameters, search for regimes of high-resoluted recording could be complicated. The presented article proposes the way to analyze the hard-to-reach regimes of laser recording by modeling them with more convenient regimes (with different geometric and/or thermochemical parameters) based on their physical similarity.

Mechanism of pulsed-laser-induced oxidation of titanium films

An axisymmetric model of 50 nm titanium thin film on glass substrate is proposed to study the mechanism of pulsed-laser-induced oxidation of titanium. The oxidation rate is determined by the oxygen ions migration rate, which is significantly influenced by the laser-induced Mott potential and temperature. The oxidation processes are calculated by finite-difference time-domain method. The simulation results are in good agreement with experiment results, which verify that the laser-induced Cabrera-Mott oxidation theory is the mechanism of laser-induced oxidation of titanium. This work is beneficial to study the improvements for fabricating TiO 2 nanostructured materials on the resolution and efficiency.

Combined effects of nanosecond laser-induced surface oxidation and nanostructure formation for selective colorization of nickel surfaces

Metal surfaces can be nanostructured by laser irradiation making use of different effects ranging from thin film generation to nanostructures formation. Here, the colorization of pure nickel surfaces by nanosecond laser irradiation in air is demonstrated and studied in detail. Correlations between chromaticity coordinates and laser-processing parameter show that the accumulated fluence is the dominating factor in creation of a specific colored surface. The color of the laser-irradiated surfaces shows both angle-dependent and angle-independent in reliance on the processing conditions. The examination of the laser-colored surface demonstrates that lateral and vertical organized, laser-induced structures with nano-, micro-, and mesoscopic scales can be found simultaneously which contribute to the colorization in a particular manner. A comprehensive analysis of the processes involved in the color formation at nickel was performed by examining the surfaces by SEM, reflectometry, XPS, and XRD to verify the multi-process mechanisms of color formation. The most saturated colors result from interference effects within the redeposited layers. It was found that controlling the hatching distance applying optimized laser fluence enables a wider color range and allows a very precise setting of the color. Based on the extracted laser-processing parameters, the surface coloration of arbitrary pattern with desired optical properties becomes practicable, and nanosecond laser color marking can, therefore, be expanded to potentially new applications.

Tribological performance of metal-reinforced ceramic composites selectively structured with femtosecond laser-induced periodic surface structures

The impact of femtosecond (fs) laser-induced periodic surface structures (LIPSS) on tribological properties was investigated for metal-reinforced ceramic composites (Al2O3-ZrO2-Nb). For this purpose, the metallic niobium (Nb) phase was selectively structured with LIPSS in an air environment with different values of the fs-laser peak fluence by near-infrared fs-laser radiation (λ = 1025 nm, τ = 300 fs, frep = 1 kHz), taking advantage of the different light absorption behavior of ceramic and metal. The tribological performance was evaluated by reciprocating sliding tests in a ball-on-disc configuration using Ringer's solution as lubricant. The surfaces were characterized before and after laser irradiation by optical microscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and by measuring the contact angle with Ringer's solution. The LIPSS formation resulted in an increased wetting of the surface with the lubricant. Moreover, the selectively structured composite surfaces revealed a coefficient of friction significantly reduced by a factor of ~3 when compared to the non-irradiated surface. Furthermore, the formation of a laser-induced oxidation layer was detected with NbO as the most prominent oxidation state. Selectively structured composites with outstanding mechanical properties and enhanced tribological performance are of particular interest for biomedical applications.

Fabrication of high aspect ratio microgroove on Ti6Al4V by laser-induced oxidation assisted micro milling

High aspect ratio microstructures based on titanium alloys have a become driving demand for various fields such as aerospace, biomedicine, and turbine blades due to their high strength, low density, biocompatibility, and corrosion resistance. However, high aspect ratios in micro-machining domains come up with low material removal rate, poor machined microstructure quality, premature tool failures, and slow machining efficiency. In this paper, a novel hybrid processing method of laser-induced oxidation assisted micro milling (LOMM) is proposed to solve the aforementioned problems. The oxidation behavior of Ti6Al4V under nanosecond laser irradiation, cutting force, machined surface quality, burr formation and tool wear mechanisms were investigated. A microgroove on Ti6Al4V alloy with a width of 0.5 mm and an aspect ratio of 5.4 was fabricated successfully by LOMM. For comparison, the conventional micro milling (CONV) was also carried out to fabricate a high aspect ratio microgroove under the same cutting parameters. Under laser irradiation, a loose oxide layer and relatively dense sub-layer were formed. The thicknesses of the oxide layer and sub-layer were 18.2 μm and 2.3 μm, respectively. The cutting force and tool wear rate in LOMM were tremendously low in removing the oxide layer compared to those in CONV. The surface quality machined by LOMM was superior to that produced by CONV. The tool wear mechanisms observed in LOMM was coating spalling, while in CONV tool nose breakage, coating spalling and adhesive wear were observed. Compared to CONV, the tool service life in LOMM was prolonged significantly.

LIPSS on thin metallic films: New insights from multiplicity of laser-excited electromagnetic modes and efficiency of metal oxidation

Thin Cr films 28-nm thick deposited on glass substrates were processed by scanning low-intensity femtosecond laser pulses with energy well below single-pulse damage threshold. Two types of laser-induced periodic surface structures (LIPSS) were produced, depending on the scanning velocity, (1) parallel to laser light polarization with periodicity somewhat smaller than laser wavelength and (2) perpendicular to polarization with spatial period much smaller than wavelength. All structures are formed as protrusions above the initial film surface and exhibit a high degree of oxidation. To explain formation of the LIPSS and their conversion from one to another type, a rigorous numerical approach for modeling surface electromagnetic waves in thin-film geometry has been developed, which takes into account the change of optical properties of material due to laser-induced oxidation and porosity. The approach addresses the multiplicity of electromagnetic modes allowed for thin films. It has been found that the low spatial frequency LIPSS parallel to laser polarization, which are formed at low scanning velocities, are well described by the Sipe theory for surfaces of low roughness. The SEW mode responsible for high spatial frequency LIPSS formation at high scanning velocities has been identified. The mechanisms of optical feedback and transformation between types of LIPSS with scanning velocity have been proposed.

Study on laser-induced oxidation assisted micro milling of Ti6Al4V alloy

The micro-scale machining of titanium alloy has many problems such as severe tool wear, low machining efficiency, and poor machined surface quality. This paper presented a novel processing method of laser-induced oxidation assisted micro milling (LOMM). The morphology and phase compositions of the surface layer and subsurface layer under laser irradiation, as well as the morphology of the machined microgroove, were investigated. The effects of micro milling parameters on cutting force, surface roughness, and top burr width were studied in detail. The burr formation mechanisms and tool wear mechanisms were revealed. A comparison study of LOMM and conventional micro milling in terms of cutting force, machined surface quality, and tool wear was conducted. A porous oxide surface layer and relatively dense subsurface layer were formed under laser irradiation. The cutting force and tool wear in removing the oxide surface layer was extremely low compared with those in removing the substrate material. Feed per tooth had a significant effect on the cutting force, surface roughness, and top burr width. For the investigated range of parameters, the optimal feed per tooth and cutting depth were 3.5 μm/z and 6 μm, respectively. The tool wear mechanisms in LOMM were coating spalling, and in conventional micro milling were tool nose breakage, coating spalling and adhesive wear. Under the same cutting parameters and cutting length, LOMM effectively decreased the cutting force, slowed the tool wear, and prolonged the service life of tool.

Laser-induced oxidation assisted micro milling of spark plasma sintered TiB2-SiC ceramic

Abstract In this work, a novel process of laser-induced oxidation assisted micro milling (LOMM) was proposed. TiB2-SiC ceramic with hardness of 24.6 ± 0.8 GPa was prepared by spark plasma sintering and used as the workpiece material. The cutting force, surface quality and tool wear mechanisms were investigated. Under laser irradiation and oxygen assistance, a porous oxide layer and relatively dense sub-layer were formed. The hardness of the sub-layer was found to be 12.8 ± 0.7 GPa which was far lower than that of the substrate. Both the cutting and thrust forces increased with increasing the feed per tooth and depth of cut in micro milling of the sub-layer material. The material removal mechanism was dominated by a transition from ductile to brittle mode as the feed per tooth increased from 0.3 μm/z to 1.2 μm/z. The surface roughness Ra of 46 nm was achieved when the cutting speed, feed per tooth and depth of cut were 31.4 m/min, 0.3 μm/z and 2 μm, respectively. The tool wear mechanism was characterized by the flank wear and coating spalling. As a case study, a micro slot having width of 0.5 mm and aspect ratio of 2 was fabricated by the LOMM. For comparison, the conventional micro milling was also carried out using the same cutting parameters. The surface quality fabricated by LOMM was better than that by the conventional micro milling. The machining efficiency in LOMM was improved by 104% as compared to the conventional micro milling.

Adhesion and corrosion resistance of laser-oxidized titanium in potential biomedical application

This study presents an analysis of the impact of the oxide layers, prepared by means of laser radiation in ambient air with different process parameters, on the morphology, corrosion resistance and adhesion properties of titanium grade 2. The samples were irradiated in and out of the focal plane, using a commonly-available fiber laser (Yb:glass) system. The microscopic examination, colorimetry, roughness, chemical Raman analysis, electrochemical tests (electrochemical impedance spectroscopy) as well as adhesion, wettability and scratch-tests were conducted. The study has shown that laser oxidation, depending on the choice of process parameters, can contribute to both the improvement and deterioration of the surface quality, including the size and amount of microcracks, other defects or heterogeneities, roughness, and adhesion. The samples manufactured in the focal plane exert a higher corrosion resistance, higher adhesion and lower roughness, compared to those irradiated out of the focal plane. The aim of this study was to broaden the knowledge about the nature and influence of laser-induced oxidation in and out of the focal plane on selected properties of oxide layers.

Study on oxidation behavior of spark plasma sintered TiB2[sbnd]SiC ceramic under laser irradiation

In this paper, TiB2SiC ceramic with a Vickers hardness of 24.6 ± 0.8 GPa is prepared by spark plasma sintering. A novel method of using laser-induced oxidation to assist micro milling of the TiB2SiC ceramic is proposed. The microstructure and phase composition of the material after laser irradiation are studied. The oxidation mechanism is revealed. Under laser irradiation, an oxidation reaction between ceramic and oxygen takes place, forming a loose and porous oxide layer which is easy to remove. The effects of average laser power, scanning speed and reaction environment on the oxidation behavior of TiB2SiC ceramic are investigated in detail. The results indicate that the thickness of the oxide layer increases with an increase in the average laser power and a decrease in the scanning speed. A thick and stable oxide layer is formed in an oxygen-rich environment. The thickness of the subsurface layer is independent of the reaction environment. For the investigated range of parameters, the optimal laser parameters are average power of 5 W and scanning speed of 1 mm/s, under which the thicknesses of oxide and subsurface layers are 51 μm and 15 μm, respectively, in an oxygen-rich environment.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ВЗАИМОСВЯЗИ ИЗМЕНЕНИЙ КОЭФФИЦИЕНТОВ ПРОПУСКАНИЯ И ОТРАЖЕНИЯ ПЛЕНОК ЦИРКОНИЯ ПРИ ПРЯМОЙ ЛАЗЕРНОЙ ЗАПИСИ

The paper is devoted to study of the characteristics of thin metal films of zirconium in laser-induced oxidation in order to create a technology for direct laser writing of high-resolution diffractive optical elements. To study the optical characteristics of the recorded structures, we used the method of direct detection of the transmission of microstructures using an optical microscope with video camera. Quantitative characteristics of the dependences of the transmission of the irradiated film on the laser beam power on samples with a film thickness of 80 nm were obtained. The regime of nano-grating formation has been found and studied qualitatively.

Erasing and rewriting of titanium oxide colour marks using laser-induced reduction/oxidation

Laser-induced oxidation of metallic surfaces such as titanium is used in many application areas for colour marking due to its selectivity, cleanness and processing speed. However, as the generated colours are permanent this reduces the flexibility and applicability of this laser processing technology. Therefore, a method is reported in this paper to erase selectively the oxide-based colours using laser-induced oxygen reduction. Especially, the colour marks are reprocessed in a low oxygen environment employing a nanosecond laser. A low fluence was used in order to diffuse oxygen out into the atmosphere and yield a lower form of metal oxides or a pure metal. Any cumulative fluence exceeding 25 J/cm2 was sufficient to erase any laser-induced colours on titanium substrates. The XPS analysis revealed that all fields were mainly comprised of TiO2 prior to erasing with only small contributions from Ti2O3 and TiO/TiN. Following the proposed laser-induced oxygen reduction, the relative concentration of TiO2 decreased substantially while the overall amount of Ti in the near surface region increased. The results clearly show that the erasing of oxide-based colour marks is only due to oxygen diffusion back into the atmosphere and there were not any signs of laser ablation.

Oxidation behaviour of composite CrN/(Cr,V)N coatings with different contents of vanadium induced by UV nanosecond laser pulses

The oxidation behaviour and morphological modification of CrN/(Cr,V)N coatings on Si wafers were studied after UV nanosecond laser (wavelength 248 nm, pulse duration 25 ns) processing in ambient air. The evolution of the surface composition and microstructure with the number of accumulated/subsequent pulses was systematically analysed depending on the initial content of vanadium in the as-deposited coatings. Irradiation of CrN/(Cr,V)N coatings with different content of vanadium was carried out at a fluence of 0.17 J cm−2 with different number of pulses. The concentration of metallic components was fairly homogeneous distributed throughout the sample. However, on surface and in sub-surface regions the contents of Cr and V are diminished due to laser-induced oxidation. The composition and thickness of forming oxides mixture, Cr2O3 and V2O5, are depending on the number of applied laser pulses and the initial vanadium content. The asymmetric progress of surface morphology is characterized by the formation of grainy structures at peripheries and the appearance of cracks and irregular closed shapes in the centre of the irradiation area.

Influence of oxygen pressure on the fs laser-induced oxidation of molybdenum thin films

We present a study of femtosecond (1028 nm, 230 fs, 54.7 MHz) laser processing on molybdenum (Mo) thin films. Irradiations were done under ambient air as well as pure oxygen (O2) at various gauge pressures (4, 8, 12 and 16 psi). Our results indicate that the high heating rates associated with laser processing allow the production of different molybdenum oxides. Raman spectroscopy and scanning electron microscopy are used to characterize the molybdenum oxidation for the different irradiation and oxygen pressures parameters chosen showing a high correlation between well-defined oxidation zones and the oxygen pressure surrounding the samples during the irradiation of the Mo thin films.

On femtosecond laser shock peening of stainless steel AISI 316

In this paper we report on the competition in metal surface hardening between the femtosecond shock peening on the one hand, and formation of laser-induced periodic surface structures (LIPSS) and surface oxidation on the other hand. Peening of the stainless steel AISI 316 due to shock loading induced by femtosecond laser ablation was successfully demonstrated. However, for some range of processing parameters, surface erosion due to LIPSS and oxidation seems to dominate over the peening effect. Strategies to increase the peening efficiency are discussed.

Effect of iron and nanolites on Raman spectra of volcanic glasses: A reassessment of existing strategies to estimate the water content

The effect of iron content and iron nanolites on Raman spectra of hydrous geologically-relevant glasses is presented. Current procedures to estimate the water content using Raman spectra were tested to explore potential effects of iron content, its oxidation state, and nanolites on models' reliability. A chemical interval spanning from basalt to rhyolite, including alkali- and iron-rich compositions, with water content up to 5.6wt% was investigated using two spectrometers. When considering nanolite-free samples, the area of the band at 3550cm−1 linearly correlates with the sample water content regardless of chemical composition. Using this approach, data were reproduced with a root-mean-square error (RMSE) of ~0.15wt%. Depending on the sample chemistry, water content, and acquisition conditions the laser-induced sample oxidation led to underestimating the water content up to ~90% with a long acquisition time (26min). Normalising the water band region to the silicate band region minimises such a limitation. The area ratio between these bands linearly correlates with the water content and the use of different baseline procedures does not remove the dependence of such a correlation by the iron content and its oxidation state. With this procedure, data were reproduced with a RMSE of ~0.16wt%. For both approaches, the presence of iron nanolites may result in underestimating the water content.