• Journal of the Korean Society for Heat Treatment
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• v.10 no.3
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• pp.198-208
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• 1997

The-steady-state creep mechanism and behavior of Zircaloy-4 used as cladding materials in PWR have been investigated in air environment over the temp, ranges from 600 to $645^{\circ}C$ and stress ranges from 4 to $7kg/mm^2$. The stress exponents for the creep deformation of this alloy, n were decreased 4.81, 4.71, 4.64, and 4.56 at 600, 615, 630 and $645^{\circ}C$, respectively; the stress exponents decreased with increasing the temperature and got closer to about 5. The apparent activation energies, Q, were 62.1, 60.0, 57.9 and 55.4 kcal/mole at stresses of 4, 5, 6, $7kg/mm^2$, respectively; the activation energies decreased with increasing the stress and were close to those of volume self diffusion of Zr in Zr-Sn-Fe-Cr system. In results, it can be considered that the creep deformation for Zircaloy-4 was controlled by the dislocation climb over the ranges of this experimental conditions. Larson-Miller parameter, P, for the crept specimens was obtained as P=(T+460)(logt,+23). The failure plane observed by SEM slightly showed up intergranular fracture at this experiment ranges. However, it was essentially dominated by the dimple phenomenon, which was a characteristics of the transgranular fracture.

• Nuclear Engineering and Technology
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• v.45 no.1
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• pp.73-80
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• 2013

The primary water stress corrosion cracking (PWSCC) of Alloy 600 in a PWR has been reported in the control rod drive mechanism (CRDM), pressurizer instrumentation, and the pressurizer heater sleeves. Recently, two cases of boric acid precipitation that indicated leaking of the primary cooling water were reported on the bottom head surface of steam generators (SG) in Korea. The PWSCC resistance of Ni base alloys which have intergranular carbides is higher than those which have intragranular carbides. Conversely, in oxidized acidic solutions like sodium sulfate or sodium tetrathionate solutions, the Ni base alloys with a lot of carbides at the grain boundaries and shows less stress corrosion cracking (SCC) resistance. The role of grain boundary carbides in SCC behavior of Ni base alloys was evaluated and effect of intergranular carbides on the SCC susceptibility were reviewed from the literature.

• Corrosion Science and Technology
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• v.3 no.6
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• pp.233-239
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• 2004

Primary water stress corrosion cracking of steam generator tubings occur on many tubes in pressurized water reactors(PWRs), and they are repaired using sleeves or plugs. In order to develop proper repair criteria, it is necessary to know the leak behavior of the tubes, which have stress corrosion cracks. Crack development tests were carried out on the tubes at room temperature, and leak rate and burst pressure were measured on the degraded tubes at room temperature and a high temperature. No leakage was detected on the tubes where 100 % through wall crack developed, at 1560 psi, which is an operating pressure difference of pressurized water reactors(PWRs). In some tests, leak rates of the tubes increased with time at a constant internal water pressure. A test tube showed a very small amount of leakage at 2700 psi in a high temperature pressure test at $282^{\circ}C$, but it disappeared after the pressure increased slightly. Even cracks are 100 % through wall, they need to open in order to reach a certain amount of leak rate at the operating pressure difference.

• Corrosion Science and Technology
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• v.2 no.2
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• pp.59-67
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• 2003

Electrochemical potentiokinetic reactivation (EPR) tests are used to evaluate the degree of sensitization (DOS) of stainless steels and nickel base alloys. The validity of EPR test to detect DOS of these alloys, however, depends all the electrolyte composition employed. The existence of precipitates such as NbC, and TiC, etc. in the alloys also affects the reactivation behaviors of these alloys. In this investigation, the reactions involved during EPR processes are analyzed. In 0.5 M $H_2SO_4$+ 0.01 M KSCN electrolyte, a reactivation peak associated with the localized attack around NbC, different from that of intergranular corrosion, is observed for the solution annealed 347 SS. For solution annealed Alloy 600, matrix corrosion and localized attack around TiC with distinct anodic peaks appeared in the EPR curves are seen in the $H_2SO_4$+ KSCN electrolyte. With proper adjustment of elect rolyte composition, the contribution from intergranular corrosion, as a result of chromium carbide precipitation along the grain boundaries, can be distingui shed from the matrix and localized corrosion for the sensitized Alloy 600.

• Journal of the Korean Society of Industry Convergence
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• v.5 no.4
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• pp.367-372
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• 2002

Experimental study was conducted for lapping process after WEDMed specimen. In order to decide the lapping depth of the specimen, the number of the grain size was increased from 400, 600 to 800 to obtain the better surface. Observation of scanning electron microscope, hardness test, surface roughness test and energy dispersive spectrum(EDS) analysis were used for this experimental study. From the comparison and analyses of the results of between the wire-cut electrical discharge machining and the lapping, the following results were obtained. The surface roughness after lapping was found to be improved as increasing the number of lapping process like 1st, 2nd, 3rd lapping and the number of grain size such as 400, 600, 800. The surface hardness after increasing the lapping depth of the specimen was slowly increased. It was found that after 3rd lapping process the hardness was reached the hardness of original base material. It was found that the small amount of coating components within 3% was remained after the 1st lapping process, compared to that approximately 16% after WEDM process.

• Nuclear Engineering and Technology
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• v.54 no.12
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• pp.4481-4490
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• 2022

In this study, a new rupture disk corrosion test (RDCT) method was developed for real-time detection of stress corrosion cracking (SCC) initiation of Alloy 600 in a primary water environment of pressurized water reactors. In the RDCT method, one side of a disk specimen was exposed to a simulated primary water at high temperature and pressure while the other side was maintained at ambient pressure, inducing a dome-shaped deformation and tensile stress on the specimen. When SCC occurs in the primary water environment, it leads to the specimen rupture or water leakage through the specimen, which can be detected in real-time using a pressure gauge. The tensile stress applied to the disk specimen was calculated using a finite element analysis. The tensile stress was calculated to increase as the specimen thickness decreased. The SCC initiation time of the specimen was evaluated by the RDCT method, from which result it was found that the crack initiation time decreased with the decrease of specimen thickness owing to the increase of applied stress. After the SCC initiation test, many cracks were observed on the specimen surface in an intergranular fracture mode, which is a typical characteristic of SCC in the primary water environment.

• Korean Journal of Materials Research
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• v.17 no.9
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• pp.484-488
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• 2007

Mo(Ti) alloy and pure Cu thin films were subsequently deposited on $SiO_2-coated$ Si wafers, resulting in $Cu/Mo(Ti)/SiO_2$ structures. The multi-structures have been annealed in vacuum at $100-600^{\circ}C$ for 30 min to investigate the outdiffusion of Ti to Cu surface. Annealing at high temperature allowed the outdiffusion of Ti from the Mo(Ti) alloy underlayer to the Cu surface and then forming $TiO_2$ on the surface, which protected the Cu surface against $SiH_4＋NH_3$ plasma during the deposition of $Si_3N_4$ on Cu. The formation of $TiO_2$ layer on the Cu surface was a strong function of annealing temperature and Ti concentration in Mo(Ti) underlayer. Significant outdiffusion of Ti started to occur at $400^{\circ}C$ when the Ti concentration in Mo(Ti) alloy was higher than 60 at.%. This resulted in the formation of $TiO_2/Cu/Mo(Ti)\;alloy/SiO_2$ structures. We have employed the as-deposited Cu/Mo(Ti) alloy and the $500^{\circ}C-annealed$ Cu/Mo(Ti) alloy as gate electrodes to fabricate TFT devices, and then measured the electrical characteristics. The $500^{\circ}C$ annealed Cu/Mo($Ti{\geq}60at.%$) gate electrode TFT showed the excellent electrical characteristics ($mobility\;=\;0.488\;-\;0.505\;cm^2/Vs$, on/off $ratio\;=\;2{\times}10^5-1.85{\times}10^6$, subthreshold = 0.733.1.13 V/decade), indicating that the use of Ti-rich($Ti{\geq}60at.%$) alloy underlayer effectively passivated the Cu surface as a result of the formation of $TiO_2$ on the Cu grain boundaries.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.403-403
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• 2010

The Pt-Ni alloy is an electro-catalyst of interest in the low temperature direct methanol fuel cells(DMFCs). It has been already reported that the Pt-Ni alloy catalysts may even have enhanced activity compared to pure platinum catalyst, depending on how the surfaces are prepared. The order-disorder transition in bimetallic alloy such as $\beta$-CuZn, Cu3Au, and CuAu have been investigated greatly by x-ray diffraction. After annealing the bimetallic alloy, the crystal structure changes as observed in the order-disorder transition of Cu3Au which changes from the face centered cubic to a simple cubic structure. Pt-Ni bimetallic alloy has been already reported to have the face centered cubic structure. However, in nano-scale Pt-Ni bimetallic alloy crystals the crystal structures changes to a simple cubic structure. In this experiment, we have studied the order-disorder transition in Pt-Ni bimetallic nanocrystals. Pt/Ni thin films were deposited on sapphire(0001) substrates by e-beam evaporator and then Pt-Ni alloy were formed by RTA at 500, 600, and $700^{\circ}C$ in a vacuum environment and Pt-Ni nano particles were formed by RTA at $1059^{\circ}C$ in a vacuum environment. We measured the structure of Pt-Ni bimetallic alloy films using synchrotron x-ray diffraction and SEM.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.17-24
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• 2011

To investigate the relationship between heat treatment in zirconium alloy tubing process and metallurgical characteristics of Zr-1Nb-0.69Sn-0.11Fe alloy tubes, mechanical and oxidation behaviors of tubes heat treated at different temperatures after the final pilgering were investigated. The stress strain curves exhibited the saturation behaviors in all heat treatment conditions ($460{\sim}600^{\circ}C$) in this study with the onset strain of saturation increased with increase of post-pilgering annealing temperature. The strength fell off rapidly with increasing annealing temperature. The ultimate strength of the low tin Zr-1Nb-0.69Sn-0.11Fe alloy with slightly higher iron and oxygen contents in this study was found to be higher than Zr-1Nb-1Sn-0.1Fe alloy. The oxidation experiments in steam condition revealed that the corrosion resistance of low tin Zr-1Nb-0.69Sn-0.11Fe alloy was better than the Zr-1Nb-1Sn-0.1Fe alloy with a higher Sn content. The weight gain of low tin Zr-1Nb-0.69Sn-0.11Fe alloy tubes gradually increased with the increasing annealing temperature possibly due to the decreased Nb content in the matrix because of the formation of ${\beta}-Nb$ particles.

• Journal of Ocean Engineering and Technology
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• v.22 no.6
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• pp.58-63
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• 2008

The short-term high temperature creep rupture behavior of Ni-based Alloy718 steels jointed by friction welding wasinvestigated at the elevated temperatures of 550 to $700^{\circ}C$ under constant stress conditions. The creep rupture characteristics such as creep stress, rupture time, steady state creep rate, and initial strain were evaluated. Creep stress has a quantitative correlation between creep rupture time and steady state creep rate. The stress exponents (n, m) of the experimental data at 550, 600, 650 and $700^{\circ}C$ were derived as 26.1, -22.4, 22.5, -18.5, 17.4, -14.3 and 6.9, -8.1, respectively. The stress exponents decreased with increasing creep temperature. The creep life prediction was derived by the Larson-Miller parameter (LMP) method and the result equation obtained is as follows: T(logtr+20)=-0.00148${\sigma}^2$-3.089${\sigma}$+23232. Finally, the results were compared with those of the base metal for Alloy718.