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The high-temperature oxidation behavior of two Fe-29%Ni-17%Co (Kovar) alloys with different Mo additions was investigated at temperatures ranging from 1190℃ to 1250℃ under an N2 + O2 environment. And then, the effect of surface oxidation and Mo addition on the hot ductility of the Fe-Ni-Co alloy has been studied. The oxidation weight gain increased with increasing temperature and increasing oxygen content in the N2 + O2 environment. The oxidation resistance of the Kovar alloy apparently improves with the addition of Mo. On the other hand, surface analysis using EPMA, ESCA, and XRD revealed that the oxide scale formed in these two alloys consisted mainly of three different external oxide layers (Co-based oxide, Fe2O3, (Fe, Ni)Fe2O4) as well as the internal oxide layer of NiO. Mo was found to be strongly segregated on the boundary between the internal and external oxidation layers and consequently believed to play an important role particularly in decreasing the thickness of the internal oxide layer. Regardless of the alloy composition, the formation of oxide layer was found to have minimized the hot ductility of the Kovar alloy significantly. Grain boundary micro-cracks in the internal oxide region were also noted following deformation due to high temperature, one of which acting as a notch that caused the poor hot workability of the oxidized specimen. The addition of Mo to the Kovar alloy could also retard the decrease in the hot ductility of the oxidized specimen through the prevention of notching due to internal oxidation.

keyword : Low thermal expansion, Kovar, High temperature oxidation, Hot ductility, Mo

Since the aircraft accidents caused by fatigue failure far less the service life estimated in 1950`s, damage tolerance design concept assuming pre-crack existence on the aircraft structures was introduced, and crack growth measurement was requested to correlate theoretical fatigue crack growth rate by modifying the theoretical analysis parameters. In this study, 3 specimens from 3 different structure tests (coupon test, component test and full scale test) were selected and examined to verify fatigue crack growth rate. Before starting metallographical observation to each fracture surface, each test spectrum was truncated to select high load points and SEM observation was done to match well developed striations on the fracture surface to the selected load points. Also characteristic analysis technique effective to each structure test was suggested and confirmed through this study. With the crack growth data obtained by fractographic analysis, it is possible to give the information to correlate the test result data to the analysis result data. Eventually damage tolerance design concept will be used for an aircraft development with increased structure integrity and reliability.

keyword : Fractographic analysis, Fatigue Life, Damage tolerance

In order to purify the catalytic grown MWNTs, a new method using rapid cooling heat treatment was tried out. The CNTs heated at 900℃ had been quenched with solid CO2 coolant, then 30%HNO3 refluxing treatment was carried out for 1hour. 30%HNO3 refluxing treated CNTs for 8hours and 35%HCl washing treatment + 30%HNO3 refluxing treated CNTs for 4hours were also prepared, respectively. The morphology and purity were estimated by the means of TEM observation, powder XRD, EDX, and ICP analysis. The investigation of BET surface area and pore characteristics were conducted also by N2 adsorption at 77 K. From the results of experiments, it was found that the purity of 99.7 wt.% MWNTs could be obtained by rapid cooling associated method. In addition, the BET surface area of rapid cooling treated MWNTs increased significantly. It was assumed that rapid cooling treatment promoted the development of mesopores not only by the opening of MWNTs tip but also by the bursting of nanotubes caused by thermal shock effect.

keyword : Carbon nanotubes, Catalytic growth, Purification, Rapid cooling

Ag substrate with {113}<121> texture was to be developed for Tl-1223 high temperature superconductor (HTS) in this study. Since Ag would not react chemically with Tl-1223 HTS, the buffer layers, generally used between HTS and substrate, are not needed. However, the texture control of Ag is not easy task due to the low stacking fault energy. Previous study revealed that Tl-1223 {00l} almost parallels Ag {113} crystallographically. To obtain {113}<121> texture of Ag, a mechanical and thermal treatment method was used after 97% cold rolling and 300℃ heat-treatment. Ag {113}<121> texture formed tends to be disappeared as the abnormal grain growth and secondary recrystallization occur by heating at 850℃, Tl-1223 crystallization temperature. It was found that plastic deformation of 0.5% and 850℃ heat-treatment was an effective way to avoid secondary recrystallization and to keep {113}<121> texture of Ag substrate.

keyword : Ag substrate, Rolling, Mechanical-thermal treatment, {113}<121> texture, Secondary recrystallization, ODF, orientation distribution function, T1-1223 HTS, high temperature superconductor

The low carbon steels were oxidized isothermally at temperatures of 1100-1200℃ in air and CO2/O2 mixed atmosphere for up to 2 hr in air, and their oxidation characteristics were examined. The oxidation characteristics in air and mixed atmosphere were similar. The low carbon steels oxidized quite fast, forming scales that consisted mainly of Fe2O3 and (FeO+Fe3O4) from the surface. Beneath the thick, nonadherent oxide scales, internal oxide precipitates formed.

keyword : Steel, Oxidation, Air, Oxygen, Carbon Dioxide

This article represents that the flexural failure in a LOC (lead-on-chip) package begins from the brittle fracture of the plastically-encapsulated silicon chip. Thus, in order to enhance the flexural strength of the LOC package, it is very important to prevent the brittle fracture of the silicon chip embedded in the plastic package body. It was investigated in the present work how the fracture strength of the LOC package depends on the depth and orientation of grinding-induced defects on the back-surface of the silicon chip. It was found that the grinding-mark orientation rather than the grinding-mark depth on the back surface of the silicon chip is a more important factor in determining the fracture strength of the LOC package.

keyword : Silicon chip, LOC package, Grinding mark, Defect, Fracture

Submicron nickel powders were prepared in aqueous solution through a thermal-reduction process. The effect of reaction conditions on the morphology and particle size of Ni powders are discussed. X-ray diffraction and SEM were employed to characterize the products. SEM showed that the average particle size was 0.3 ㎛ having spherical shape with narrow size distribution at optimum condition. The reduction rate of Ni^(2+) was above 90%.

keyword : Nickel Powder, MLCC, Hydrotlermal

The influence of bonding materials on the field emission of CNT(carbon nanotube) cathodes was investigated with respect to the vacuum level. The vacuum level was controlled by gases(O2, H2) exposure. An OCNT(organic binder with CNT) cathode and an ICNT(inorganic binder with CNT) cathode were fabricated using different composition of CNT pastes which have organic or inorganic bonding materials. The emission current decreased in the case of OCNT cathode but increased in the case of ICNT cathode as the vacuum level decreased from 10(-7) Torr to 10^(-4) Torr by the exposing oxygen. From this study, we found that the effect of surface cleaning, increasing emission current, by ion bombardment in the ICNT cathode was more dominant than adsorption but adsorption in the OCNT cathode was more dominant than ion bombardment.

keyword : Field emission, Paste material, Carbon nanotube, Degradation

Ball shear tests for ball grid array (BGA) solder ball joints were investigated in terms of the effects of test parameters, i.e., shear height and shear speed. Two kinds of Pb-free solder compositions were employed in this study: Sn-3.5Ag-0.75Cu and In-48Sn. Substrate was a common solder mask defined (SMD) type with solder bond pad openings of 460 ㎛ in diameter. Shear tests were conducted with the two varying test parameters. It was observed that increasing shear height at a fixed shear speed has the effect of decreasing shear force for both Sn-3.5Ag-0.75Cu and In-48Sn solder joints, while the shear force increased with increasing shear speed at a fixed shear height. It should be noted that the shear forces of In-48Sn solder joints were more highly affected by the shear speed rather than those of Sn-3.5Ag-0.5Cu solder joints. Shear heights that were too high had some negative effects on the test results such as unexpectedly high standard deviation values or shear tip sliding from the solder ball. Low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces.

keyword : Shear height, Shear speed, Finite element analysis, Pb-free solder, Ball grid array

Metallic foam materials with high porosity were fabricated by melt foaming method. The structure of Al foam has homogeneous distribution of cell size. The pore diameter was increased with increasing holding time at optimum foaming temperature. We have been tried to control pore diameters and cell wall thickness for kinetic analysis by Ostwald ripening. In our experimental results, it was found that there were a closed relationship between radius of developing pores and holding time as 1.5 mm at 120 second, 1.75 mm at 300 second, 2.0 mm at 600 second and 3.5 mm at 1200 second. We can conclude that the evolution process of pore in molten aluminum must be Ostwald ripening. That means that hydrogen diffusion through pore walls from smaller pores to a larger one is the main process of pore evolution at least in the latter period of holding.

keyword : Ostwald ripening, Metal foam, Pore size, Holding time, Diffusion gas