Papers by Keyword: Laser Surface Modification

Abstract: Mg is a biodegradable metal that possesses excellent biocompatibility, bioactivity, nontoxic degradation products, and unique mechanical properties. These characteristics make it an attractive element to be used as implant material in physiological environments because it biodegrades and has excellent biocompatibility and bioactivity. In addition, an excess of magnesium ions does not result in cellular toxicity in the human body, where it is often getting rid along with urine. The most significant disadvantage of magnesium is its uncontrolled quick corrosion rate, which can cause rapid loss in mechanical qualities. As a consequence, this might cause the implant to fail before the tissue has completely healed.The purpose of this research is to improve the surface features of the implant, as well as to control the rate at which magnesium corrodes and, as a result, the concentration of magnesium ions that are released into the surrounding environment. This will be accomplished by coating the implant surface with a composite biodegradable polymer (Polycaprolactone PCL) matrix reinforced with MgO Nano-particles which will act as a protective layer to increase the corrosion resistance of magnesium implants. In addition, a laser surface modification procedure was implemented in order to improve the surface's qualities and make certain that there is a strong adhesion between the coating and the surface of the substrate. In order to increase the surface roughness of the specimen, (Nd: YAG) laser device was utilized to create pulses on the surface of the specimen.

Abstract: Nucleation and growth conditions of single-crystallinity control are convincingly elaborated by multi-scale mathematical modeling of heat and mass transport to totally abate undesirable weld defects, e.g. disoriented crystal and hot cracking inside molten pool of nonequilibrium crystallization, in order to illustrate the usefulness of predictive capability through theory and experiment procedures. Crystal growth is complicated by crystallinity-dependent thermal and chemical driving forces in front of dendrite tip during viable laser surface modification of Ni-based single-crystal superalloy. These two thermal metallurgical determinants play crucial role in crack-insusceptible columnar crystal growth, which is favorably oriented throughout weld depth. There is particular challenge in complete elimination of disoriented crystal, i.e. stray grain formation, for acceptable surface quality. Conservative (001)/[100] crystalline orientation is desired to diminish Al concentration and supersaturation, and morphologically satisfy epitaxial growth kinetics to successfully lessen central cracking with satisfactory variability of laser power and welding speed. Comparatively, (001)/[110] crystalline orientation is disadvantageous to asymmetrically augment Al concentration and supersaturation and aggressively increase interface instability, microstructure heterogeneity and hot cracking vulnerability along disoriented crystal boundaries. Disoriented crystal is increasingly withstood if the Al concentration and supersaturation in front of dendrite tip are low enough and crack-unsusceptible part is relatively large enough in case of attractive (001)/[100] crystalline orientation with optimal range of heat input to ameliorate microstructure homogeneity. Crystalline orientation region varies with diverse welding configurations, and epitaxy across solid/liquid interface is also sensitive to heat input of laser processing, which necessitate high efficient welding conditions optimization. Considerable effort is made to distinguish diffusion-driven crystal growth between a series of combinations of multiple welding conditions, such as critical welding configuration and heat input. Metallographically, the morphologies of crystal growth and hot cracking are experimentally observed to consistently support kinetics calculation result and well explain correlation between solidification behavior and crystal growth.

Abstract: This paper investigates the effect of fiber laser surface modification of AISI 316L austenitic stainless steel on corrosion behavior. In the experiments, the fiber laser with center wavelength of 1062 nm was employed with various laser parameters of beam velocity and laser frequency. The laser-treated has performed on the specimen surface in order to form the melted layer with an argon gas shielding. The electrochemical tested results showed that the laser-treated increases 40% pitting potential. Moreover, the results also exhibited corrosion potential shift to more positive potential. On the basis of the findings on the corrosion improvement, it can be concluded that the pitting potential of the material can be improved by a corrosion protective layer from the new laser-treated surface.

Abstract: A microsecond pulsed laser beam was used to local magnetic domain modification of electrical grain oriented silicon steel. It was carried out using three different laser pulse regimes: a single pulse laser regime, a multipulse laser regime and a multipulse laser regime with modulation of laser pulses. The laser processing variables were pulse energy and and number of pulses. The samples were tested for nanohardness and coercivity before and after laser treatment. Light optical microscopy, scanning electron microscopy and magnetic force microscopy were used to observe the cross-sectional profile, surface of the samples, and magnetic domain visualization, respectively. The local laser treatment of grain oriented silicon steel surface has been studied in terms of its influence on the magnetic domains and coercivity. It was found that laser-modified samples showed coercivity improvement in comparison to the non-treated samples. The most significant improvement in coercivity was obtained in the modulated multipulse regime and negligible improvement in the single pulse laser regime. Three main effects responsible for the observed improvement were identified, namely: magnetic domain refinement, influence of number of laser pulses and shape of laser HAZ profile. The present work highlights on differences in the magnetic domain structure, microstructure of the laser modified material and basic electromagnetic and mechanical properties. In present study, the pulse laser surface processing was presented as a useful energy efficient alternative to other techniques e.g. mechanical scribing, electrical discharge scribing, plasma jet scribing, etc. The refined magnetic domains in electrosteels are responsible for the observed low coercivity, which indicates perspective application of the investigated laser modified steels in the power transformer cores with lower core losses.

Abstract: This paper presents laser surface modification of gray cast iron for enhanced surface hardness properties. A 300 W high power Nd:YAG laser system with pulse mode was used to modify gray cast iron samples surface. Laser processing was conducted using a 3³ full factorial design. Three controlled parameters were laser power, pulse duration and overlap percentage. The modified surface was characterised for metallographic study, roughness and hardness. Metallographic study and surface morphology were conducted using optical microscope while hardness properties were measured using Vickers scale. Surface roughness was measured using a 2D stylus profilometer. The results show that hardness of laser modified surface increased due to grain refinement. The overlapping rates increased significantly with decreasing laser scanning speed which affected sample surface integrity. Low surface roughness obtained at the highest scanning speed of 1400 mm/min, and low power of 830 W with pulse repetition frequency of 50 Hz. Process optimization was carried out for maximum surface hardness and laser modified depth, and minimum surface roughness. These findings indicate potential application of cast iron for high wear resistant applications through laser surface modification.

Abstract: This paper presents laser surface modification process of plasma sprayed yttria stabilized zirconia (YSZ) thermal barrier coating (TBC) for enhanced hardness properties and low surface roughness. A 300W JK300HPS Nd: YAG laser was used to process YSZ TBC sample surface. The parameters selected for examination were laser power, pulse repetition frequency (PRF) and residence time. Micrographs of the TBC system were captured using EVO 15 Scanning Electron Microscope (SEM). Surface roughness was measured using 2-dimensional stylus profilometer. X-ray diffraction analysis (XRD) was conducted to measure phase crystallinity of the laser-modified coating surface. X-ray diffraction patterns were recorded in the 2θ range of 10 to 80° using Bruker D8 Advance system with 0.7Å wavelength from a copper source (~1.5Å). The laser modified surface exhibited higher crystallinity compared to the as-sprayed samples. The presence of tetragonal phase was detected in the as-sprayed and laser processed samples. The hardness properties of laser modified TBC increased 15% of the as-sprayed sample. These finding are significant to development of thermal barrier coating design optimization for enhanced surface properties of semi-solid forming die.

Abstract: Titanium and titanium alloys are widely used in aeronautical, marine, chemical and biomedical applications and so on, owing to their specific properties such as good corrosion resistance, low densities, high specific strength and modulus, and high-temperature resistance. However titanium and titanium alloys also have many disadvantages, such as low hardness, low wear-resistance and the low corrosion-resistance in some cases, which limit their wider application. Recent years, the corrosion resistance of titanium and titanium alloys is required to elevate in some fields. Proper surface modification can solve the problems effectively. This paper reviews the recent investigations of laser surface modification to improve the corrosion resistant of titanium and its alloys. The microstructures, the corrosion resistance properties, and the influence factors of the coatings were discussed systematically. And the future prospect of the further researches and uses is presented.

Abstract: This paper presents laser surface modification of AISI 1025 low carbon steel for enhance surface hardness properties. An Nd:YAG laser system with pulse mode was used in order to modify 10mm thick plate surface. Three controlled parameters were laser power, pulse duration and overlap percentage which ranged from 100W to 200W, 0.4 to 1.0ms and 50% to 90% respectively. The treated samples was characterised for metallographic study and hardness. Metallographic study was conducted using optical microscope for laser modified layer thickness and grain size. Hardness properties were measured using Vickers indenter. The result show that hardness of laser treated area increased due to fine grain size produced in the laser modified layer. The overlapping rates increase significantly with decreasing laser scanning speed. These findings are important high wear applications.

Abstract: The interaction between femtoseocnd laser and transparent materials has been studied intensively in recent years. When the femtosecond laser was focused onto the surface of the transparent materials, if the laser fluence applied to the sample exceeds the material’s fluence threshold, ablation occurs. In this paper, we study the surface ablation of lithium niobate by femtosecond laser. We produced a two-dimensional array of voids in the sample surface by varying the number of shots and laser energy, and analyze of the damage depth with the relation to the pulse energy and the number of the pulse. It has important reference on the microfabrication in such materials by femtosecond laser.

Abstract: Laser surface modification of nine tool steels, namely, plastics mold steels (PMSs), high-speed steels (HSSs) and cold/hot-work steels (CHWSs), was achieved by means of a CW Nd:YAG laser. The microstructure and the phases present in the surface of the specimens were analyzed by optical microscopy, scanning-electron microscopy and X-ray diffractometry. The surface hardness of the specimens was measured using a Vickers microhardness tester. The corrosion characteristics of the laser surface-melted steels in 3.5 wt% NaCl solution at 25 oC were studied by potentiodynamic polarization technique. The microstructures of the surface of the steels were changed completely after laser surface melting. Some steels showed improved corrosion resistance compared with the conventionally hardened specimens due to dissolution of the alloying elements in solid solution. The hardness and corrosion characteristics of all the laser surface-melted specimens are strongly dependent on the amount of passivating elements in solid solution and also on the morphology of the re-precipitated carbides. Both these factors depend on the laser processing parameters and the substrate compositions.