• Laser Solutions
• /
• v.12 no.3
• /
• pp.18-22
• /
• 2009

Experimental results for the laser shock peening of stainless steels, duplex stainless steel and STS304, for the enhancement of surface hardness are reported. A high power Nd:YAG laser (532 nm, 2nd harmonics) was used to irradiate the workpiece in water at the irradiances of 5, 10, $15\;GW/cm^2$. The surface of a workpiece was covered with Fe or Al foil for protection of the original surface and reduction of laser reflection. The laser pulse densities were varied from $25\;pulse/mm^2$ to $75\;pulse/mm^2$. In the case of the STS304, the surface hardness increased with increasing pulse density and the maximum increase of about 29% was achieved using Fe foil at $10\;GW/cm^2$ and $75\;pulse/mm^2$ conditions. The maximum increase in surface hardness of duplex stainless steel was about 8% at $10\;GW/cm^2$ and $75\;pulse/mm^2$ with also Fe foil. In the case of the Al foil, less increase of surface hardness was obtained, possibly due to the thermal expansion effect.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.14 no.5
• /
• pp.897-903
• /
• 2011

The objective of this study is to investigate the thermal behavior on material surface and the variation in the surface morphology of aluminum 6061 alloy by the Nd:YAG pulsed-laser irradiation. First, we predicted the surface temperature variation during pulsed-laser irradiation by using the two dimensional finite element analysis. When the pulsed-laser of 133 mJ energy and 5 ns pulse duration is irradiated on the surface of aluminum alloy, the material surface is thought to be melting because the surface temperature rises steadily up to about $660^{\circ}C$ exceeding the melting point. Also, the experimental results show that the solidification microstructure has been developed clearly after surface melting. Second, the diameter of melted zone was analysed by finite element analysis and measured by OM(Optical Microscopy). It increased logarithmically with increase in the number of laser irradiation. In addition, AFM(Atomic Force Microscopy) measurement showed an increase in the average surface roughness during pulsed-laser irradiation.

• Journal of Welding and Joining
• /
• v.34 no.6
• /
• pp.35-41
• /
• 2016

The experimental study has been performed through residual stress using the Ti6Al4V, investigate the effect of laser shock peening on laser welding process residual stress of Ti6Al4V welds in a reduce safety weld zone. This research evaluated the effects of shock waves from laser shock peening with a pulsed Nd:YAG laser on Ti6Al4V welding specimens, through the analysis of the residual stress of the specimens. The residual stress could be formed by the depth of 1 mm if the proposed method of reducing the residual stress is performed in the optimal condition. The welded structures and products during the production process increase the mechanical property of repeated stress, which could be expected to extend the fatigue life of the structure.

• Korean Journal of Metals and Materials
• /
• v.50 no.7
• /
• pp.539-544
• /
• 2012

Thermal shock behavior of TiN-coated SUS 304 substrate was investigated using a laser ablation method. By short surface ablation with a pulse Nd-YAG laser, considerable surface crack and spalling were observed, whereas there were few oxidation phenomena, such as grain growth of TiN crystallites, nucleation and growth of $TiO_2$ crystallites, which were observed from the coatings quenched from $700^{\circ}C$ in a chamber. The oxygen concentration of the ablated coating surface with the pulse laser also had a lower value than that of the quenched coating surface by Auger electron spectroscopy and electron probe micro analysis. These results were attributed to the fact that the properties of the pulse laser method have a very short heating time and so the diffusion time for oxidation was insufficient. Consequently, it was verified that the laser thermal shock test provides a way to evaluate the influence of the thermal shock load reduced oxidation effect.

• Journal of the Korean Society of Industry Convergence
• /
• v.22 no.4
• /
• pp.447-457
• /
• 2019

The intelligent sensory system is required to ensure the accurate welding performance. This paper describes the development of an intelligent vision sensor for the robotic laser welding. The sensor system includes a PC based vision camera and a stripe-type laser diode. A set of robust image processing algorithms are implemented. The laser-stripe sensor can measure the profile of the welding object and obtain the seam line. Moreover, the working distance of the sensor can be changed and other configuration is adjusted accordingly. The robot, the seam tracking system, and CW Nd:YAG laser are used for the laser welding robot system. The simple and efficient control scheme of the whole system is also presented. The profile measurement and the seam tracking experiments were carried out to validate the operation of the system.

• Nuclear Engineering and Technology
• /
• v.55 no.11
• /
• pp.4159-4166
• /
• 2023

Laser decontamination of radioactive surfaces is an innovative technology. Our contribution to improving this technology includes studies on laser beam decontamination with a pulsed laser of an average power of 150 W, equipped with a hand guided working head. Our investigations are focused on metallic surfaces typical in nuclear power plants, such as stainless steel, bright and rusted mild steel, galvanized steel, and painted steel. As typical nuclides of contaminated surfaces we chose Co-60 and Cs-137, the most frequently occurring nuclides in many nuclear plant components; Sr-85 as a representative of Sr-90, the potentially most harmful fission nuclide; and Am-241 as a representative of the minor alpha-radiation emitting actinides. Here, we present our results of decontamination and recovery ratios. Decontamination ratios of 90-100% were achieved on different surfaces.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.23 no.4
• /
• pp.167-172
• /
• 2013

Titanium dioxides nanoparticles coated aluminum oxide powders were fabricated by pulsed laser deposition (PLD) with Nd : YAG laser at 266 nm. The Pulse laser energy is 100 mJ/pulse. During the irradiation of the focused laser on the $TiO_2$ target, Ar gas is supplied into the chamber. The gas pressure is varied in a range of $1{\times}10^{-2}$ to 100 Pa. Titanium dioxides nanoparticles deposited aluminum oxide powders were characterized by using energy dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HR-TEM), in order to understand the effect of Ar background gas on surface morphology and properties of the powders. The coated $TiO_2$ nanoparticles had nanosized spherical shape and the crystallite sizes of 10~30 nm. The morphology of coated $TiO_2$ nanoparticles is not affected by gas pressure. However, the particle size and crystallinity slightly increased with the increase of gas pressure. According to this technique, the size and crystallinity of nanoparticles can be easily controlled by controlling pressure during the laser irradiation.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.10
• /
• pp.346-351
• /
• 2018

Metal three-dimensional (3D) printing technologies are mainly classified as powder bed fusion (PBF) and direct energy deposition (DED) methods according to the method of application of a laser beam to metallic powder. The DED method can be used to fabricate fine and hard 3D metallic structures by applying a strong laser beam to a thin layer of metallic powder. The PBF method involves slicing 3D graphics to be a certain height, laminating metal powders, and making a 3D structure using a laser. While the DED method has advantages such as laser cladding and metallic welding, it causes problems with low density when 3D shapes are created. The PBF method was introduced to address the structural density issues in the DED method and makes it easier to produce relatively dense 3D structures. In this paper, thin lines were produced by using PBF 3D printers with stainless-steel powder of roughly $30{\mu}m$ in diameter with a galvano scanner and fiber-transferred Nd:YAG laser beam. Experiments were carried out to find the optimal conditions for the width of a line depending on the processing times, laser power, spot size, and scan speed. The optimal conditions were two scanning processes in one line structure with a laser power of 30 W, spot size of $28.7{\mu}m$, and scan speed of 200 mm/s. With these conditions, a minimum width of about $85.3{\mu}m$ was obtained.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.21 no.5
• /
• pp.214-217
• /
• 2011

A fresnoite glass-ceramics has been investigating considerably because of the second order nonlinearity as well as its permanent optical nonlinearity. However, the chemical compositions of transparent glass-ceramics examined in the previous studies have been limited to adjust the composition close to fresnoite stoichiometrically. In this study, to investigate the effect of strontium ions in glass-ceramics on second order nonlinearity, $K_2O-TiO_2-SiO_2$ (KTS) glasses soaked in molten $Sr(NO_3)_2$ were prepared. Crystalline phases of the soaked glasses were measured by X-ray diffraction (XRD) as soaking times and additional heat treatment. The exchange of strontium ions into the glass was verified by Field Emission Scanning Electron Microscope (FE-SEM). And the phenomena of second order harmonic generation (SHG) was observed using Nd-YAG laser.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2007.11a
• /
• pp.354-358
• /
• 2007

An experimental study was performed to understand spray characteristics of the slinger injector. system for the micro turbojet engine. In this fuel injection system, fuel is sprayed and atomized in the combustor by centrifugal forces of engine shaft. This experimental apparatus consist of a high speed rotating Spindle, slinger injector, pressure tank and acrylic case. The droplet size and velocity were measured by PDPA(Phase Doppler Particle Analyzer) and spray was visualized by using Nd-Yag laser-based flash photography. From the test results, the droplet size(SMD) is largely affected to rotational speed, mass flow rate and the number of injection orifice. From the this experimental study, we could understand the spray characteristics of the slinger injection system and obtain the optimum shape of the slinger injector nozzle which is suitable for the micro turbojet engine.