• Journal of Welding and Joining
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• v.20 no.6
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• pp.809-815
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• 2002

Metallurgical behavior of laser welded cold rolled low carbon steel was investigated. Welding was performed with CW Nd:YAG laser system. Applied laser power, travel speed and nitrogen blowing pressure were 720W CW, 17mm/s and 196kPa, respectively. According to the test results, many carbide particles were observed on the base metal surface that was polished and etched with nital solution. The carbide particles at the welding heat affected zone were thought to be dissolved during welding process. Microstructural inspection revealed that dissolved carbide particles formed mixed phase of very fine martensite and bainite. Test results also demonstrated that the hardness of matrix remained constant value of around 160Hv over the welding heat affected zone. Dissolved carbide particles, however, showed higher average hardness values of around 276Hv near the fusion boundary and 700Hv at the welding heat affected zone of 0.4mm apart from the fusion line. It was considered that care should be given to minimize the test error when measuring the hardness value since many of the dissolved particles were so small that it was not easy to aim the indentor of the testing machine just on the objects.

• Journal of Welding and Joining
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• v.30 no.5
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• pp.70-75
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• 2012

This study is related to the laser weldability of AZ31B magnesium alloy, an all-purpose wrought alloy with good strength and ductility. In general, AZ31B is classified into AZ31B-H24 and AZ31B-O depending on temper designation. Thus, in this study, the laser weldability of AZ31B-H24 and AZ31B-O was investigated and compared. CW Nd:YAG laser was used to produce bead and butt joints. And the effects of welding conditions on the weldability of these joints were examined in detail. As a result of this study, AZ31B-H24 was found to have thinner oxide film and smaller grain size compared with AZ31B-O. Due to such difference, in bead welding, AZ31B-H24 had more wide welding range for full penetration compared with AZ31B-O. Furthermore, it was also confirmed that AZ31B-H24 and AZ31B-O have different welding conditions to obtain stable keyhole in butt welding.

• Laser Solutions
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• v.4 no.3
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• pp.30-39
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• 2001

This work was tamed out to apply a laser welding technique in joining between a Zn coated low carbon steel plate(SECC) and a free cutting carbon steel shaft(SUM24L) with or without W coating. Experiments were carried out and analysed by applying the FD(factorial design)method to obtain the optimum Laser welding condition. Optical microscopy, SEM, TEM and XRD analyses were performed in order to observe the microstructures in the fusion zone and the HAZ. Mechanical properties of the welded specimens were examined by microhardness test, tensile test and twist test. There was no flawed Zn in the fusion zone by EDS analysis. This means that during the welding process, Zn gas could be eliminated by appropriate shielding gas flow rate and butt welding gap. Ni coating itself did not influence on the tensile strength and hardness. However, twist bending strength and the weld depth of the Ni-coated free cutting carbon steel were lower as compared with those of the uncoated free cutting carbon steel. It was attributed to a lower absorbance of laser beam to the shin Ni surface. According to the results of the factorial design tests, the twist bending strength of welded specimens was primarily affected by pulse width, laser power, frequency and speed.

• Journal of the Korean Ceramic Society
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• v.37 no.12
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• pp.1187-1191
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• 2000

정방정형 지르코니아를 상온에서 안정화시키는 이트리아와, 지르코니아의 저온 열화을 억제하고 파괴강도의 증가에 기여하는 알루미나를 YAG(5Al$_2$O$_3$.3Y$_2$O$_3$) 졸의 형태로 m-ZrO$_2$와 알루미나의 혼합 slurry에 첨가하여, m-ZrO$_2$를 yttria 안정화 지르코니아로의 in situ 변환과 동시에 알루미나의 분산도를 향상시키고자 하였다. 20wt% 알루미나-지르코니아(YSZ)의 복합체 (20ATZ)를 1450$^{\circ}$~150$0^{\circ}C$에서 상압소결하여 0.5$mu extrm{m}$ 이하의 균일한 미세구조로 얻었다. 이 복합체는 정방정형 지르코니아와 $\alpha$-알루미나 상으로만 이루어지었고, 소결밀도 >99% TD이었다. 제조된 복합체의 파괴강도는 810 MPa로, 고상법으로 $Al_2$O$_3$와 3Y-ZrO$_2$분말로부터 제조된 시편의 682 MPa 보다 약 20% 향상되었고, 파괴인성은 5.52 MPa.m$^{1}$2/로 고상법으로 제조된 시편의 5.39 MPa.m$^{1}$2/과 비슷하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05c
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• pp.118-122
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• 2001

The ${\beta}-SiC+TiB_2$ ceramic electroconductive composites were pressureless-sintered and annealed by adding 12wt% $Al_2O_3+Y_2O_3$(6 : 4wt%) powder as a function of sintering temperature. The relative density is over 78.83% of the theoretical density and increased with increasing sintering temperature. The phase analysis of the composites by XRD revealed of $\alpha$-SiC(6H), $TiB_2$, $Al_5Y_2O_{12}$ and $\beta$-SiC(15R). Flexural strength showed the highest of 140 MPa for composites sintered at $1900^{\circ}C$. The vicker's hardness increased with increasing sintering temperature and showed the highest of 4.07 GPa at $1900^{\circ}C$. Owing to YAG, the fracture toughness showed the highest of 4.07 $MPa{\cdot}m^{1/2}$ for composites at $1900^{\circ}C$. The electrical resistivity was measured by the Pauw method from $25^{\circ}C$ to $700^{\circ}C$. The electrical resistivity of the composites showed the PTCR(Positive Temperature Coefficient Resistivity).

• Korean Journal of Optics and Photonics
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• v.15 no.5
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• pp.449-454
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• 2004

The optical limiter is an optical component which reduces laser beam intensity for the protection of eyes and light sensors. Carbon nanotube is now known as a highly efficient optical limiting material. Optical limiting effect of the multi-walled carbon nanotube suspensions, in several kinds of solvents such as distilled water, chloroform, ethanol and ethylene glycol, were measured in the range from room temperature to near to the boiling points of the solvents. The pulsed Nd:YAG laser whose wavelength is 1064 nm and pulse duration is 6 ns was used as a light source. The experimental result shows that the limiting efficiency was reduced as the temperature increased, and the suspension which has lower boiling point, viscosity and surface tension has highest efficiency.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.40-43
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• 2011

최근, 레이저 초음파 영상화 기법은 구조물의 비접촉식 손상 진단을 위해 널리 연구되고 있다. 초음파 영상화 기법의 가장 큰 장점은 비접촉식으로 구조물의 손상을 진단할 수 있고, 가진 및 측정 지점을 자유로이 이동할 수 있다는 점이다. 따라서 이는 고온이나 동적상태의 구조물에 적용이 가능하며, 시간과 공간상의 충분한 데이터를 획득할 수 있으므로 역문제 (Inverse problem)를 해결할 필요 없이 완전한 초음파의 전파 형상을 얻을 수 있다. 지난 연구들에서는 충분한 가진력 혹은 측정 민감도를 확보하기 위해 가진 레이저와 부착형 센서의 조합이나 부착형 가진 트렌스듀서와 센싱 레이저의 조합으로 초음파 영상을 획득하고자 하였다. 하지만 이들 조합은 가진 혹은 측정 지점이 구조물에 부착되어 있어 완전한 비접촉식 기법을 구현하지 못하였다. 이를 극복하고자 레이저와 EMAT 센서 등의 조합이 시도되어 왔으나, 이 또한 EMAT 센서의 적용 거리에 따른 한계점을 지니고 있다. 본 연구에서는 가진 레이저 (Nd:Yag)의 스캐닝을 통해 다양한 가진 점에서 발생된 초음파가 탄성체 구조물을 통해 전파되고, 이를 센싱 레이저 (Laser Doppler Vibrometer)를 이용하여 측정함으로써 비접촉식 초음파 영상화를 구현하였다. 나아가, 정상파 필터(Standing-wave filter)를 이용하여 구현된 초음파 영상으로부터 손상 영향만 검출해 내는 기법을 개발했다. 개발된 기법은 복합재 시편의 층간박리 (Delamination) 진단을 통해 검증하였다.

• Korean Journal of Optics and Photonics
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• v.8 no.6
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• pp.450-455
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• 1997

A pulsed Ti:sapphire laser with a Z-folded cavity, which was pumped by a freqeuncy-doubled Nd:YAG laser, was developed. It shows 120 nm wavelength tuning range from 740 nm to 860 nm with 90 nm FWHM under a pumping energy of 3 mJ with 18% output coupler. Using a birefringent filter, the effective efficiency was improved about 10 times compare to without a birefringent filter. The output energy obtained was $\365mu$Jwith 4 nm FWHM. And the wavelength tuning range was broadened to about 160 nm within an output energy fluctuation of $\pm$10%.

• Korean Journal of Materials Research
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• v.11 no.9
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• pp.792-796
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• 2001

For electron beam lithography and SEM(scanning electron microscopy) applications, miniaturized electrostatic lenses called a microcolumn have been fabricated. In this paper, we report the fabrication technique for 20~30$\mu\textrm{m}$ apertures of electron lenses based on silicon and Mo membrane using an active Q-switched Nd:YAG laser. Experimental conditions of laser micromachining for silicon and Mo membrane are improved. The geometrical structures, such as the diameter and the preciseness of the micron-size aperture are dependent upon the total energy of the laser pulse train, laser pulse width, and the diameter of laser spot.

• Journal of Environmental Science International
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• v.8 no.6
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• pp.699-704
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• 1999

The Photodegradation efficient of total organic compounds in the drinking water has been studied using the methods of photocatalytic reaction and laser beam irradation. The results are summarized as follows; 1. The photodegradation efficiency of total organic compounds shows as $50\%\;to\;80\%$ as within one hour and after this the efficiency is decreased slowly. 2. The photodegradation efficiency of total organic compounds shows as 65 to $90\%$ within 3.3min. when Nd : YAG beam is irradiated to the water layer. 3. An excellent observation of the organic compound removal efficiency gives revealed in that case of the longest wavelength of 532nm is irradiated among the three kinds of laser beam sources of 532nm, 355nm and 266nm. 4. The organic compound removal efficiency shows high in the case of UV beam irradiation in the thin layer of water. However the efficiency is not depended on the thickness of water layer severely. 5. The removal efficiency of the organic compounds in the direct irradiation shows higher than the indirect irradiation in the case of UV beam, but the efficiency is not depended on the direction of irradiation in the case of Nd : YAG beam irradiation.