• Journal of Welding and Joining
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• v.18 no.2
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• pp.213-213
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• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7NO1 spot-welded by pulse Nd: YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed: center line crack($C_{C}$), diagonal crack($C_{D}$), and U shape crack($C_{U}$). Also, HAZ crack($C_{H}$), was observed in the HAZ region, furthermore, mixing crack($C_{M}$), consisting of diagonal crack and HAZ crack was observed.White film was formed at the hot crack region in the fractured surface after it was immersed to 10%NaOH water. In the case of A5083 alloy, white films in C crack and $C_D crack region were composed of low melting phases, Fe₂Si$Al_8$ and eutectic phases, Mg₂Al₃ and Mg₂Si. Such films observed near HAZ crack were also consist of eutectic Mg₂Al₃. In the case of A7N01 alloy, eutectic phases of CuAl₂, $Mg_{32}$ (Al,Zn) ₃, MgZn₂, Al₂CuMg and Mg₂Si were observed in the whitely etched films near $C_{C}$ crack and $C_{D}$ crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Si in the case of A7N01 aooly, respectively.The $C_{D}$ and $C_{C}$ cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of $C_{M}$ crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The $C_{U}$ crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification. (Received October 7, 1999)

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.295-296
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• 2006

• Proceedings of the Korean Vacuum Society Conference
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• 2003.02a
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• pp.205-205
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• 2003

• Journal of Welding and Joining
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• v.12 no.1
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• pp.28-37
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• 1994

본 소고에서는 Al-Zn-Mg 계통의 고강도 알루미늄합금의 제조과정에서 실시하는 열처리 공정을 통해 얻어지는 시효경화 효과, 합금원소 첨가에 따른 석출물의 생성과 이에 따른 석출경화 효과와 용착금속의 응고균열 발생과의 상호관계를 조사하고 용접열영향부의 용질원자 확산과 입계의 liquid film에 의한 액화(liquation) 균열의 생성을 분석하여 설명하고자 한다.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.834-839
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• 2001

Calandria tube wrapping each pressure tube is one of the key structural components of CANDU reactor(Calandria) which is consisted of many pressure tubes containing nuclear fuel assemblies. As the Calandria tube(made of zirconium alloy) is sagging due to its thermal and irradiation creep during the plant operation, it possibly contacts with liquid injection nozzle crossing beneath the Calandria tube, which subsequently results in difficulties on the safe operation. It is therefore necessary to check the gap for the confirmation of no contacts between the two tubes, Calandria tube and liquid injection tube, with a proper measure during the life of plant. In this study, an ultrasonic measurement method was selected among several methods investigated. The ultrasonic device being developed for the measurement of the gap was introduced and its preliminary performance test results were presented here. The gap between LIN and CT at site was measured using by this ultrasonic device at site.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.134-138
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• 2005

The structural analysis and water pressure test of regenerative liquid rocket thrust chamber cooling channel specimens are performed at room temperature. material properties of copper alloy are obtained by uniaxial tension test at room temperature and used of elastic-plastic structural analysis. The plate type of cooling channel specimen are manufactured and performed water pressure test in order to confirm the analysis results. The differences between results of elastic-plastic analysis and that of water pressure test of cooling channel specimen are small and find that manufacturing process affect the structural stability of cooling channel very much because cooling channel thickness is small

• Korean Journal of Materials Research
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• v.19 no.2
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• pp.115-118
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• 2009

The use of dolomite refractories has increased during the past several years in the manufacturing of clean steel during the stainless steelmaking process. However, at the same time, the use of dolomite refractories has led to what is known as the skull formation. In the present work, to understand the skull formation, the wetting characteristics of dolomite substrates by liquid Fe-19wt%Cr-10wt%Ni alloys in various oxygen partial pressures were initially investigated at 1753K using the sessile drop technique. For comparison, the wetting characteristics of alumina substrates were investigated with the same technique. It was found that the wetting index, (1+$cos{\theta}$), of dolomite is approximately 40% higher compared to those of alumina. In addition, the oxygen partial pressure to generate the surface oxide, which may capture the liquid metal on the refractory surface, for dolomite is much lower than that for alumina. From this study, it was concluded that the use of dolomite is much more closely associated with the skull formation compared to the use of alumina due to the stronger wettability and the surface oxide formation at a lower oxygen partial pressure of dolomite.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.151-155
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• 2006

Elastic-viscoplastic structural analysis is performed for regenerative cooling chamber of liquid rocket thrust chamber using Bodner-Partom visco-plastic model. Strain rate test was also conducted for a copper alloy at various temperatures in order to get material constants of visco-plastic model used in the structural analysis. Material constants of visco-plastic model were obtained from strain rate test results and visco-plsstic model was incorporated into finite element program, Marc, by means of user subroutine. The structural analysis results indicate that the deformation of cooling channel is mostly caused by thermal loading rather than pressure loading and confirmed structural stability of the cooling channel under operating condition.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.177-183
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• 2005

In this work, Inconel 600, Inconel 625 and Haynes 230 are welding using Nd:YAG laser and electron bear. These heat-resistant alloys are typically used for the liquid thruster. To examine, the affects of experimental parameters on weld ability, the plate welding of these materials were carried out using both Nd:YAG laser and electron bear. Also, the micro-structure, micro-hardness, and tensile strength of the specimens were analyzed. from the analysis of the experimental results of laser and electron beam welding, we have obtained the optimal welding conditions.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.4
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• pp.69-76
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• 2006

Elastic-viscoplastic structural analysis has been performed for regenerative cooling chamber of liquid rocket thrust chamber using Bodner-Partom visco-plastic model. Strain rate test was conducted for a copper alloy at various temperatures in order to get material constants of visco-plastic model used in the structural analysis. Material constants of visco-plastic model were obtained from strain rate test results and visco-plastic model was incorporated into finite element program, Marc, by means of a user subroutine. The structural analysis results indicated that the deformation of cooling channel is mostly caused by thermal loading rather than pressure loading and confirmed structural stability of the cooling channel under the operating condition.