• Proceedings of the KWS Conference
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• 2000.04a
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• pp.139-143
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• 2000

Laser beam weldability of Zircaloy-4 was investigated using a pulsed Nd:YAG laser of 550W average power. Mechanical properties and microstructure of laser butt welded Zircaloy-4 test specimens were examined. The influence of laser generated during laser welding was analyzed and optimum laser welding parameters were investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.889-897
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• 2011

In this work, we investigated the theoretical forming limit models for Zircaloy-4 and Zirlo used for spacer grid of nuclear fuel rods. Tensile and anisotropy tests were performed to obtain stress-strain curves and anisotropic coefficients. The experimental forming limit diagrams (FLD) for two materials were obtained by dome stretching tests following NUMISHEET 96. Theoretical FLD depends on FL models and yield criteria. To obtain the right hand side (RHS) of FLD, we applied the FL models (Swift's diffuse necking, M-K theory, S-R vertex theory) to Zircaloy-4 and Zirlo sheets. Hill's local necking theory was adopted for the left hand side (LHS) of FLD. To consider the anisotropy of sheets, the yield criteria of Hill and Hosford were applied. Comparing the predicted curves with the experimental data, we found that the RHS of FLD for Zircaloy-4 can be described by the Swift model (with the Hill's criterion), while the LHS of the FLD can be explained by Hill model. The FLD for Zirlo can be explained by the S-R model and the Hosford's criterion (a = 8).

• Proceedings of the Korean Nuclear Society Conference
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• 2003.05a
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• pp.233.1-233.1
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• 2003

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.10
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• pp.1239-1249
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• 2013

In this study we establish a process to predict hardening behavior considering the Bauschinger effect for zircaloy-4 sheets. When a metal is compressed after tension in forming, the yield strength decreases. For this reason, the Bauschinger effect should be considered in FE simulations of spring-back. We suggested a suitable specimen size and a method for determining the optimum tightening torque for simple shear tests. Shear stress-strain curves are obtained for five materials. We developed a method to convert the shear load-displacement curve to the effective stress-strain curve with FEA. We simulated the simple shear forward/reverse test using the combined isotropic/kinematic hardening model. We also investigated the change of the load-displacement curve by varying the hardening coefficients. We determined the hardening coefficients so that they follow the hardening behavior of zircaloy-4 in experiments.

• Nuclear Engineering and Technology
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• v.19 no.2
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• pp.122-129
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• 1987

Experiments and numerical analysis have been performed to investigate the effect of preoxidation by oxidizing Zircaloy-4 specimens at a higher temperature after a period of exposure at a lower temperature. The oxidation experiments were performed between $700^{\circ}C$ and 85$0^{\circ}C$ after Preoxidation at $650^{\circ}C$ in a steam and water mixture for 600 seconds and 1,800 seconds. As the thickness of preoxidized layer increased, the oxidation rate of preoxidized specimens at higher temperature became lower than that of as-received claddings. A transition region of oxidation rate exist in the preoxidized specimens, and the region disappeared rapidly as the oxidation temperature increased. This effect appeared more clearly at lower temperatures. According to the results of numerical analysis performed in this study, the growth rate of oxide layer thickness and weight gains were similarly affected by the thickness of preoxidized layer.

• Korean Journal of Materials Research
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• v.8 no.3
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• pp.268-273
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• 1998

Standard Zircaloy-4 sheets, charged with 230-250ppm hydrogen by the gas-charging method and homogenized at $400^{\circ}C$ for 72hrs in a vacuum, were corroded in pure water and aqueous LiOH solutions using static autoclaves at $350^{\circ}C$. Their corrosion behaviors were characterized by measuring their weight gains with the corrosion time and observing their microstructures using an optical microscope and a scanning electron microscope. The elemental depth profiles for hydrogen and lithium were measured using a secondary ion mass spectrometry(S1MS) to confirm their distributions at the oxidelmetal interface. The normal Zircaloy-4 specimens corroded abruptly and heavily at the concentration of Li ions more than 30ppm in the aqueous solution. This is due to accelerations by the rapid oxidation of many Zr- hydrides formed by the large amount of absorbed hydrogen, resulting from the increased substitution of $Li^{+}$ ions with $Zr^{4+}$-sites in the oxide as the Li ion concentration increased. The specimens that had been charged with amounts of hydrogen greater than its solubility corroded early with a more rapid acceleration than normal specimens, regardless of the corrosion solutions. At longer corrosion times. however, normal specimens showed a rather accelerated corrosion rate compared to the hydrogen-charged specimens. These slower corrosion rates of the hydrogen-charged specimens at the longer corrosion times would be due to the pre-existent Zr-hydride in the matrix, which causes the hydrogen pick- up into the specimen to be depressed, when the oxide with an appropriate thickness formed.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.148-153
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• 1998

핵연료 피복관용 신합금을 개발하기 위한 기초연구로서 Zr-xNb계 합금과, Zr-0.8Sn-xNb계 합금을 각각 4종씩 선정하였다. 이들 합금을 판재시편으로 가공한 뒤 Autoclave를 이용하여 36$0^{\circ}C$에서 부식 시험을 실시하였다. 부식과정에서 생성되는 산화막의 미세구조를 관찰하기 위해 천이 전 영역에서 동일두께를 갖도록 부식시편을 준비하여 산화막/금속계면에 대해 SEM관찰을 실시하였다. 또한 석출물의 크기와 부식과의 관계를 조사하기 위하여 부식전의 시편에 대해 TEM관찰을 실시하였다. Zr-xNb 2원계 합금에서는 Nb함량이 적을수록 부식저항성이 증가하는 경향을 보이는데, 0.2Nb가 첨가된 합금이 가장 우수한 부식저항성을 보였다. Zr-0.8Sn-xNb 3원계에서도 천이 전 영역에서는 2원계 합금과 마찬가지로 Nb함량이 적을수록 부식저항성이 증가하나, 천이 후 영역에서는 이런 경향이 바뀌는 것이 관찰되었다. 이는 Sn이 첨가됨으로서 Nb가 부식에 미치는 영향이 달라지기 때문이라 생각된다. 산화막 관찰결과, 순수 Zr은 결정립계를 따라서 산화막이 급격히 성장하는 반면에, Zircaloy-4합금은 매우 균일한 산화막 계면을 유지한다. Zr-xNb계 합금과 Zr-0.8Sn-xNb계 합금에서도 내식성이 우수한 합금은 균일한 산화막/금속 계면을 유지하는 것이 관찰되었다.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.183-188
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• 1997

핵연료 피복관용 Zr신합금을 개발하기 위해서 16종의 신합금을 설계하였다. 설계된 합금은 진공아크용해, $\beta$-열처리, 열간압연, 냉간압연 및 진공열처리의 공정에 의해 판재로 제조되었으며 이들 시편에 대해 35$0^{\circ}C$와 40$0^{\circ}C$에서 부식시험, 상온과 고온에서 인장시험 및 40$0^{\circ}C$에서 크립시험을 실시하여 신합금의 특성을 평가하였다. Zr-Nb-Sn계에 Fe, V, Te, Sb, Ru, Pd의 다른 원소를 미량 첨가하는 다원계 합금에서 Fe와 Cr은 부식특성을 향상시키는데 매우 효과적인 것으로 나타났다. Sb는 기계적강도를 향상시키고 Fe, Cr원소는 연신율을 증가시키는 원소로 밝혀졌으며 Sb와 V은 크립저항성을 매우 향상시킨다. 16종의 합금중 2-3종의 합금은 기존의 Zircaloy-4보다 우수한 내식성을 보였으며 Zr-Nb-Sn-FeCr합금은 ZIRLO와 유사한 부식저항성을 나타냈다. 부식과 크립저항성을 동시에 향상시키기 위해서는 Fe, Cr, Sb원소를 적절히 함유시킨 합금에 대해서 집중적인 연구가 수행되어야 할 것으로 사료된다.

• Nuclear Engineering and Technology
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• v.24 no.1
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• pp.75-85
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• 1992

The texture changes and their effect on the 0.2% yield strength of Zircaloy-4 sheet were examined after quenched from the ($\alpha$+$\beta$) phase temperature. When the prior ($\alpha$+$\beta$) gram size was slightly larger than that of the $\alpha$-annealed, the observed texture was similar to the $\alpha$-annealed texture having an ideal orientation of the (0001) basal pole at 30$^{\circ}$away from the normal direction toward the transverse direction. When the prior ($\alpha$+$\beta$) grain size was twice as large as that of the $\alpha$-annealed, the location of maximum basal pole intensity was distributed between the transverse and the rolling direction making an angle 15$^{\circ}$from the normal direction, and the observed texture became isotropic. It was found that the Kearns texture parameter, fr, in the rolling direction increased steadily, and fr in the transverse direction increased slightly, while fr in the the normal direction decreased with increasing heat treatment time. With a small increase in fr, the 0.2% yield strength increased drastically. The influence of texture was analyzed by deriving the Schmid orientation factors and the resolved shear stresses for the deformation systems. It was found that the large increase in the 0.2% yield strength was attributed mainly to the microstructural changes and partly to the texture changes by the ($\alpha$+$\beta$) heat treatment.