Abstract: Spectroscopic and electrostatic probe measurements were made to examine plasma characteristics under nitriding for a 10-kW-class direct-current arc plasma jet generator with a supersonic expansion nozzle in a low pressure environment. Heat fluxes into the plate from the plasma were also evaluated. Ammonia and mixtures of nitrogen and hydrogen were used as the working gas. The H-atom electronic excitation temperature and the N2 molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. As approaching the titanium plate, the thermodynamical nonequilibrium plasma came to be a temperature-equilibrium one. Both the electron number density near the plate and the heat flux increased with H2 mole fraction for mixtures gases. In cases with mixtures of N2 and H2, a radical of NH with a radially wide distribution is considered to contribute to the better nitriding as a chemically active and non heating process.
Abstract: Electroplating behavior of Bi 2Te 3 and thermoelectric properties of the electroplated Bi 2Te 3 films were investigated for nanowire application. Composition, microstructure, and thermoelectric properties of the electroplated Bi-Te films were strongly dependent upon composition of the electroplating solutions and plating current density. While the power factor of the Bi 2Te 3 film plated at a current density of 1×10-4 A/cm2 was 1.75×10-4 W/K2-m, the film formed at 5×10-4 A/cm2 exhibited the value of 3.5×10-4 W/K2-m. Substantial pore filling was achieved with electrodeposition of Bi 2Te 3
for the alumina template with 200 nm pores.
Abstract: Si 3N 4 thick coating was fabricated by reactive RF plasma spraying, in which elemental Si reacted with surrounding nitrogen plasma. It was possible to fabricate the Si 3N 4 coating by reactive spraying on a graphite substrate. As for the substrate, however, graphite is difficult to apply to the practical structural parts because of its low mechanical strength. Thus, it was necessary to realize Si 3N 4 coating onto the metal substrate. In this research, Ti alloy, carbon steel and Ni alloy were used as the metal substrates. Ti alloy was difficult to apply to the formation of Si 3N 4 coating because the preferential reaction of Ti-N prevented the nitriding reaction of Si-N. On the carbon steel substrate, pure Si coating was fabricated. However, nitriding reaction was difficult to occur on this substrate
because the melting point of carbon steel was lower than the reaction temperature of Si-N. Ni alloy, one of the useful heat-resistant alloys, was also tried as the substrate. Finally, the feasibility of some kinds of interlayer between Si 3N 4 and steel substrate was clarified to improve the bonding property between Si 3N 4 and metal substrate.
Abstract: Plasma nitrocarburizing treatment was performed for SCM 435 steel by using a pulsed plasma ion nitriding system. The effects of the variation of nitrogen and methan contents upon the hardened layer were investigated. Both the thickness of the compound layer and the amount of ε phase in the compound layer increased with nitrogen content. For an atmosphere containing 90% N2 gas content in the gas mixture, the thickness of the compound layer decreased due to the reduction of the number of nitrogen ion and slow diffusion of nitrogen atoms. The relative amount of ε phase in the compound layer increased with CH4 gas content up to 2%. For CH4 gas content over 2% in the gas mixture, the thickness of the compound layer decreased with CH4 content due to the formation of θ-Fe3C phase.
Abstract: In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. The MPD arcjet generator can produce higher-velocity, higher-temperature, higher-density and larger-area plasmas than those of conventional thermal plasma torches. Two types of MPD arcjet generator were developed for applications to mullite, zirconia and titanium-nitride spraycoatings. The MPD spray process could successfully form dense, uniform and hard ceramic coatings. In titanium nitride reactive spraying, plasma diagnostic measurement and flowfield analysis were also carried out. A large amount of N and N+ was expected to be exhausted with a high velocity from the MPD generator. Both the electron temperature and the electron number density were kept high at a substrate position compared with those for conventional low-pressure thermal
sprayings. A chemically active plasma with excited particles of N+, Ti, Ti+ and Ti2+ was considered to contribute to better titanium nitride coatings. All coating characteristics showed that the MPD arcjet generators had high potentials for ceramic spray coatings.
Abstract: Electroless copper plating was investigated for the electronics applications, such as a metallization for ULSI and MEMS etc. The role of electrolyte composition on the kinetics and mechanism of the electroless copper deposition process was described. Electrochemical techniques were employed for the investigations. The mixed potential and current were determined and then those were compared with experimental deposition rate. The kinetics is strongly influenced by the pretreatment and additive concentrations.
Abstract: The behavior of bake-hardening of the laser weldment was investigated. The bake-hardening steel(BH steel) was welded with Nd:YAG laser followed by plastic deformation and subsequent heat-treatment. Then the influence of laser welding on the behavior of bake-hardening was investigated. The hardness of the laser weld metal significantly increased after welding. After the plastic deformation, both the base metal and weld metal became harder by work-hardening. The heat treatment resulted in more increment of hardness in both the base metal and weld metal by
bake-hardening. The amount of bake-hardening reached a maximum value at the plastic strain of 5% or more. We modified a kinetic equation proposed for predicting the strength of a low-carbon bake-hardening steel and applied to the estimation of hardness of the base metal and weld metal. The calculated hardness values agree with the experimental data. The calculated activation energy for bake-hardenig was that for diffusion of carbon and nitrogen atoms in α-Fe. Thus the hardening is
thought to be governed by diffusion of these solute atoms.
Abstract: Reactions between 48Sn-52In solder and under bump metallurgies(UBM) such as 100nmTi/8µm Cu and 300nm Al/400nm Ni(V)/400nm Cu have been investigated, and the shear strength of 48Sn-52In solder bumps on each UBM has been evaluated. While intermetallic compounds with two different morphologies were continuously thickened on Ti/Cu with repeating the reflow process, the intermetallics on Al/Ni(V)/Cu spalled into the solder with increasing the number of reflow times.
The solder bumps on Ti/Cu exhibited higher shear strength than those on Al/Ni(V)/Cu.
Abstract: Interfacial reaction between electroless plated Ni-P/Au UBM(Under Bump Metallization and eutectic Sn-58mass%Bi solder was studied by using AEM(Analytical Electron Microscopy). UBM is prepared by the electroless plating of Au (0.15μm ) / Ni-15at%P (7 μm ) on bare Cu substrate, and then it is reacted with Sn-58Bi solder at 220°C for 1 min. The chemical analysis using AEM
provided us very consequential information about microstructure of the interface and phases formed. CBED(Convergent Beam Electron Diffraction) technique is used for phase identification of intermetallic compounds. In this study, the AEM results indicate that Ni3Sn is formed at the P-rich Ni layer/Ni3Sn4 interface by crystallographic analysis. The measured primitive cell volume(104.10 Å3)of this phase is close to the Ni3Sn(103.19 Å3) rather than Ni2SnP(235.24 Å3).
Abstract: The effect of welding conditions on defects, microstructure, mechanical properties and formability of CO2welded 800MPa grade TRIP steel was investigated. Bead-on-plate welding was carried out under the various welding speed in 6kW with a shield gas of Helium. Extensive porosity was observed in the joints produced at a 4m/min of welding speed but was not observed in the joints when a welding speed greater than 6m/min was used. The maximum hardness was obtained at the weld metal and the HAZ near the weld metal and was the same regardless of the welding speed. The HAZ hardness near the base metal was reduced due to retained ferrite but was higher than that of the base metal. In a parallel tensile test to weld axis, the strength of the joints was higher than that of the base metal. Elongation was found to be lower than that of the raw material because a crack was initiated in the bead at the strength levels corresponding to the tensile strength of the base metal and was propagated perpendicular to tensile direction. The formability of joints was found to be 63% that of the raw material.