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The high temperature ballooning properties of the Zircaloy-4 cladding were evaluated at the simulated Loss Of Coolant Accident (LOCA) environment. Effect of Nb on the ballooning property was also investigated, which is added in advanced cladding for the enhancement of corrosion resistance. Initially pressurized zirconium cladding in 10 MPa and 60 MPa as hoop stress was heated until rupture. Burst elongation and burst temperature was measured after the test. The results showed that phase transformation from a to R has an great influence on the deformation behavior in that a phase acts transgranular slip and 3 phase does intergranular sliding. Effect of Nb did not show significantly in high temperature ballooning property because shortage of test time was such that Nb did not affect the phase transformation.

keyword : Zirconium cladding, Loss of Coolant Accident, LOCA, Phase transformation, Niobium

With the rapid advancement in electronic industries, there is a great interest on the nano grain sized, high-purity copper, which possesses both high-strength and high-conductivity, produced by severe plastic deformation (SPD). The nano grain sized materials, in general, show the unconventional mechanical behavior as a result of extremely high density of grain boundary area causing a rapid dynamic recovery during deformation. The commercially available, high-purity copper usually contains a small amount of trace phosphorous, and the presence of such element is believed to affect the rate of dynamic recovery, and eventually tensile behavior of pure copper. In the present study, the effect of trace phosphorous on the tensile behavior of accumulative roll bond (ARB)ed high-purity copper was examined. Both 99.99% pure oxygen-free copper (OFC) and 99.9% pure deoxidized high phosphorous copper (DHP) were used for the present study. It was found that the tensile strength of OFC ceased to increase after 2 ARB process cycles, while that of DHP increased continuously with ARB process up to 8 cycles, suggesting that the presence of trace phosphorous affected the rate of dynamic recovery significantly. Finally, it was discussed how the trace phosphorous affected the tensile behavior of ARBed, high-purity copper, based on the SEM, TEM and DSC(differential scanning calorimeter) observations. (Received February 17, 2004)

keyword : ARB, OFC, DHP, Tensile behavior, Tensile strength

Superplasticity of ultra-fine grained (UFG) Ti-6A1-4V alloy processed by equal channel angular (ECA) pressing was investigated with the variation of strain rate and temperature. Initial coarse equiaxed grains (11 μm in diameter) were significantly refined to =0.3 μm without changing volume fraction after 4 times of isothermal ECA pressing at 600℃. Tensile tests of both coarse grained specimens and UFG specimens were performed at temperatures of 600℃, 650℃ and 700℃, respectively, and at strain rates of 10^(-4)/s to 10^(-2)/s. UFG structures exhibited considerably higher elongations than those of coarse grained specimens at the same conditions of temperatures and strain rates. The results indicated low-temperature superplasticity (LTS) could be achieved by using UFG structures. Also, it was found in this study that, in spite of non-equilibrium state due to intense plastic straining, grain size were found to be an important factor in controlling overall superplasticity of UFG structure. A plastic instability during superplastic deformation of UFG Ti-6A1-4V alloy was discussed in relation to Hart`s criterion. (Received June 2, 2004)

keyword : ECA pressing, Ultra-fine grain, Ti-6Al-4V alloy, Superplasticity

The texture and mechanical properties during fabrication processes - extrusion, cold rolling and aging treatment - of plate in the 7050 Al alloys without/with 0.1%Sc were investigated. In both the cross section(CS) and longitudinal section(LS) of the specimen without Sc, after cold rolling, texture of R-fiber was predominant. In the Sc added alloy after cold rolling, {112}<111>(Cu)＋weak (123)<634>(S) texture components developed in the CS of the specimen while strong (3-fiber＋(110)<001>(Goss) components developed in the LS of the specimen. After solution treatment and aging treatment, the alloy (CS and LS) without Sc had random texture, but by the alloys with the 0.1%Sc, the components of the rolling texture are not changed. After the aging treatment, hardness and tensile strength of the alloy with 0.1%Sc increased about 15% and 17%, respectively, than those without Sc. Tensile strength of the Sc added specimen was the highest along the rolling direction where the <111> texture was strongly developed. On the other hand, in the specimen without Sc, the mechanical properties were not dependent on the direction of the sample. (Received May 3, 2004)

keyword : Texture, Sc added alloy, 7050 Al alloy, Recrystallization

The consolidation behavior of Fe nanopowder synthesized by plasma arc discharge process has been investigated by using thermal dilatometry system at elevating temperature in hydrogen atmosphere. The densifications have finished at 560-620℃ and the shrinkage was divided into the first rapid densification at low temperature and then the slight retardization of shrinkage at high temperature. The highly compacted specimen having the delamination in green body could not reach to full densification due to the remaining of delamination after heat-up sintering. But low pressure compacted body presented the relatively higher sintering density of 90%T.D. after heat-up process with showing quite sound microstructure. The densification behaviors were discussed in terms of powder characteristics and microstructural development. Also innovative route for full densification, namely 3L consolidation process(low compaction - low heat up - low temperature sintering), is suggested in this study. (Received July 5, 2004)

keyword : Plasma arc discharge, Nanopowder, Compaction, 3L Consolidation

The innovative consolidation process of Fe nanopowder synthesized by plasma arc discharge process has been proposed in this study, that is 3L consolidation process, low compaction - low heat up - low temperature sintering. The compaction body of surface passivated Fe nanopowder having low compactability could easily reach to full densification(98%T.D.) at relatively low sintering temperature of 560℃ for 2 hrs. in hydrogen atmosphere with low heating rate(5℃/min.). And also the grain growth was effectively inhibited under 250 nm during low temperature sintering and 3 times larger hardness (250 Hv) could be obtained by this process with comparing to conventional sintered body. This highly ability of consolidation for PADed Fe nanopowder depends on and discussed in terms of the chacracterisitcs of nanopowder, fine powder size, complete dispersion and surface modification. (Received July 5, 2004)

keyword : Plasma arc discharge, Nanopowder, Sintering, 3L Consolidation

The effect of thermal cycling on the degradation of thermal barrier coatings has been studied. A Ni-based superalloy substrate was coated with an Al-rich NiAI or NiCoCrAlY bond coat and yttria stabilized zirconia. These specimens were exposed to two types of thermal cyclings, namely, 10 minute thermal cycling and 1 hour thermal cycling, at 1100℃ in the air. The TBC system with NiCoCrA1Y bond coat showed a longer life time in 10 minute thermal cycling compared to that with NiAI, while the TBC system with NiAl showed a longer life time in 1 hour thermal cycling compared to that with NiCoCrAlY. These degradation behaviors will be discussed in detail. (Received June 15, 2004)

keyword : Thermal barrier coating, Thermally grown oxide, NiAl, NiCoCrAlY, Thermal cycling

In the development of the advanced spent fuel management process based on the molten salt technology, it is essential to choose the optimum material for the process equipment handling molten salt. The corrosion behaviors of 304 S.S., 321 S.S., 316 LN S.S. and Incoloy 800 H in a molten salt of LiCI-Li₂O were investigated in the temperature range of 650-800℃. The oxide scales consisting of Fe₃O₄i FeCr₂O₄and Cr₂O₃ were formed in the 304 S.S., 321 S.S., 316 LN S.S. and Incoloy 800 H regardless of reaction temperature and time. The order of corrosion rate was Incoloy 800 H < 316 LN S.S. < 321 S.S. < 304 S.S.. Incoloy 800 H showed uniform corrosion behavior, whereas 304 S.S., 321 S.S. and 316 LN S.S. showed intergranular corrosion behavior. Incoloy 800 H with high Ni content exhibited the highest corrosion resistance among the examined alloys. (Received February 27, 2004)

keyword : Hot molten salt, Molten salt corrosion, Corrosion behavior, Hot corrosion

Solvent extraction experiments of Sm were performed from chloride solution with PC88A and saponified PC88A. Solvent extraction reaction of Sm with PC88A and the corresponding equilibrium constant were evaluated from the experimental and ionic equilibria data as follows Sm^(3+)_(aq)+ 1.5H₂A_(2,org)= SmA_(3,org)+ 3H^(+)_(aq) , K = 0.33. The predicted distribution coefficients of Sm agreed well with the experimental results. The distribution coefficients of Sm with saponified PC88A and the values of equilibrium pH depended on the initial extraction conditions. When the concentration of PC88A was in excess of that of Sm, saponification of PC88A greatly enhanced the extraction of Sm. (Received June 21, 2004)

keyword : SmCl3, PC88A, Extraction, Saponification, Equilibrium constant

A chemical model was developed to estimate equilibrium constant for the solvent extraction of Nd and Sm from chloride solution with saponified PC88A. The model could be employed to predict the distribution coefficient of metal from the initial extraction conditions. The model consisted of chemical equilibria, mass balance, charge balance and solvent extraction reaction. By applying the model to the experimental conditions and data, equilibrium constants for the solvent extraction of Nd and Sm were obtained. The effect of the saponification of PC88A on the extraction of Nd was explained in terms of the equilibrium constant obtained in this study and the change of equilibrium pH. The predicted distribution coefficients of Nd and Sm agreed well with those measured. (Received July 14, 2004)

keyword : NdCl3, SmCl3, PC88A, Saponification, Equilibrium constant