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It is generally accepted that Si promotes kinetics of polygonal ferrite due to thermodynamic factors such as undercooling (increase of A(e3)) and maximum amount of ferrite formed. However, in this study, it was found that the difference between the measured rates of ferrite formation in C-Mn steel and Si added steel was much larger than that expected considering only thermodynamic factors. The classical nucleation theory with pillbox model was adopted to figure out what is the most controlling factor in formation of ferrite. The volume free energy change was calculated by use of the dilute solution model. The diffusivity of carbon was formulated as functions of C and Si by using experimental data. It was found that the volume free energy change was still predominant but the kinetic factors such as interfacial energy and the diffusivity of carbon by addition of Si were not negligible at lower undercoolnig. However, with increasing undercooling, the diffusivity of C was the most effective on the ferrite kinetics, though the ambiguity of treating interfacial energy was not yet clear.

keyword : dual phase steels, Si, ferrite transformation, nucleation rate

The effect of He-injection on irradiation-induced segregation of aging treated 12%Cr-15%Mn austenitic steel for structure material of nuclear and/or fusion reactors from the point of view of the reduced radio-activation was investigated by using the 1,250kV high voltage electron microscope (HVEM) connected with an ion accelerators. Aging treated high Mn-Cr steel has been irradiated at 873K by using three modes of single electron-beam irradiation, electron-beam irradiation after He-injection and electron/He(+)-ion dual-beam irradiation in HVEM. Irradiation-induced segregation analyses were carried out by an energy dispersive X-ray analyzer (EDX) in a 200 kV FE-TEM with beam diameter of about 0.5 nm. Void formations were observed in electron-beam irradiation after He-injection and electron/He(+)-ion dual-beam irradiated specimens. Irradiation-induced segregations of Cr and Mn at grain boundary were observed in each irradiation condition. The amounts of Cr and Mn segregation decreased in the cases of He-injection compared with single electron-beam condition.

keyword : irradiation-induced segregation, he-injection, high manganese austenitic steel, electron-beam irradiation damage, HVEM, aging treatment

The damping capacity was the most important factor for development of industrial apparatus and precision apparatus. In this research, we developed Fe-12Cr-22Mn alloy having alloying elements and investigated the damping property and strength. Particularly, the effects of the phases of alpha, gamma and epsilon martensite on the damping capacity at room temperature has been investigated. Various fractions of these phases were formed depending on the Co and Si contents and degree. It was found that the combination of 22Mn-4Co-0.4Si and 50% cold rolling formed the largest volume fraction of epsilon martensite phase and showed the highest damping capacity. The other phases of alpha and gamma had actually no effect on the damping capacity. It was also found that 50% clod worked Fe-12Cr-22Mn-Co-0.4Si alloy indicated the largest Vickers hardness.

keyword : damping property, high damping material, epsilon martensite, internal friction, deformation induced martensite

In this study, SUS304 powders blended with 10 and 20 vol.% diamond particles were used to prepare SUS304/diamond binary composite coatings on Al alloy substrate by cold spray process with in-situ powder preheating. The effects of the size and toughness of diamond on microstructure of the composite coatings were investigated. Assessment of porosity, microhardness, diamond fraction, and diamond broken ratio of the composite coatings was also carried out. The results revealed that the fraction of the diamond in the coatings is about 30-60% from the original mixtures due to the difference of deposition efficiency of the diamond and SUS304 during the cold spray process. The fracture of the diamond was also found in the composite coatings due to the high impact velocity of the diamond particles. Fracturing of the diamond is mitigated with higher toughness and smaller diamond particles. However, Ti coated diamond does not present significant difference in diamond fracture behavior.

keyword : cold spray, composite coating, microhardness, SUS304/diamond, diamond broken ratio

The corrosion behavior and oxide properties of HANA-3, HANA-6 and Zircaloy-4 alloys have been investigated. HANA-3 and HANA-6 alloys showed an excellent corrosion resistance when compared to the Zircaloy-4 alloy in a PWR-simulation loop condition without a neutron flux. In HANA alloys, the corrosion rate was increased with an increase of the final annealing temperature. Oxide microstructure observation showed that the oxides formed on all the alloys had a layer structure regardless of the alloy composition. HANA-6 which was annealed at 470℃ showed the best corrosion resistance among the tested alloys and it had the highest thickness of the fully developed oxide layer even though the total oxide thickness was the smallest. The oxides were consisted mainly of columnar grains in the interface region and equixed grains in the outer surface region. The size of oxide grains was increased with an increase of the corrosion resistance and the grain morphology was changed periodically from the interface to the outer surface, which was well correlated the layer structure and the transition behavior in the corrosion kinetics. The lateral cracks were observed only in the regions where the equiaxed grains are dominant. The precipitates incorporated into the oxide of HANA alloys maintained the crystallite in the interface region but transformed to the amorphous state by oxidation when apart from the interface.

keyword : Zr alloys, corrosion, oxide

Polyimide films are extensively used as base films in FPCB and TAB. Moreover, the low adhesion strength of this interface may lead to peeling. Many studies have investigated ways to increase the adhesion strength at the interfaces. This study aimed to investigate the effects of the seed layer with an electrodeposited copper foil on the surface morphology and mechanical characteristics of copper foil, and then we show adhesion strength of between seed layer and polyimide. Platinum, palladium, Pt-Pd alloy were used as seed metals. Electrochemical experiments, in conjunction with SEM, XRD, AFM and four-point probe, were performed to characterize the morphology and mechanical characteristics of the copper foil. Large particles were observed on the surface of the copper deposition layer when a copper foil was electroplated on the Pd seed layer. However, a homogeneous surface, low resistivity and a high level of adhesion strengths were obtained when the Pt seed layer was used. The maximum value of peel strength was 1.19N/cm.

keyword : electrodeposition, Pt , Pd, Pt+Pd alloy, polyimide, peel strength

This work shows how a variation in temperature influences the flexural strength of plastic-encapsulated microelectronic packages. The experimental results manifest that the plastic packages result in more improved flexural strength than bare silicon devices below the glass-transition temperature (i.e. approximately 180℃) of their plastic body. Furthermore, the flexural strength of the plastic packages is not so sensitive to device thickening or the existence of grinding marks on the device back-surface at the low temperatures. On the other hand, at the temperatures higher than 200℃, the plastic package body was softened abruptly, resulting in a reduction in load-supporting ability. It was also found that, at the high temperatures, increased device thickness or the proper elimination of the grinding marks on the device back-surface leads to more effective suppression of flexural-induced damage potential in the plastic packages. Thus, the present experimental results suggest that an adoption of optimized back-lapping processes can allow improved reliability margins in package products during the plastic packaging process such as mold ejection.

keyword : silicon chip, plastic package, temperature, fracture