In order to examine how the solid-liquid interface responds to temperature variation depending on the materials characteristics, i.e. faceted phase or nonfaceted phase, the moving solid-liquid interface of transparent organic material, as a model substance for metallic materials (pivalic acid, camphene, salol, and camphor-50wt% naphthalene) was observed in-situ. Plots of the interface movement distance against time were obtained. The solid-liquid interface of the nonfaceted phase is atomically rough; it migrates in continuous mode, giving smooth curves of the distance-time plot. This is the case for pivalic acid and camphene. It was expected that the faceted phases would show different types of curves of the distance-time plot because of the atomically smooth solid-liquid interface. However, salol (faceted phase) shows a curve of the distance-time plot as smooth as that of the nonfaceted phases. This indicates that the solid-liquid interface of salol migrates as continuously as that of the nonfaceted phases. This is in contrast with the case of naphthalene, one of the faceted phases, for which the solidliquid interface migrates in “stop and go” mode, giving a stepwise curve of the distance-time plot.

In the DBC (direct bonding of copper) process the oxygen partial pressure surrounding the AlN/Cu bonding pairs has been controlled by Ar gas mixed with oxygen. However, the direct bonding of Cu with sound interface and good adhesion strength is complicated process due to the difficulty in the exact control of oxygen partial pressure by using Ar gas. In this study, we have utilized the in-situ equilibrium established during the reaction of + 1/2 by placing powder bed of CuO or around the Cu/AlN bonding pair at . The adhesion strength was relatively better in case of using CuO powder than when powder was used. Microstructural analysis by optical microscopy and XRD revealed that the interface of bonding pair was composed of , Cu and small amount of CuO phase. Thus, it is explained that the good adhesion between Cu and AlN is attributed to the wetting of eutectic liquid formed by reaction of Cu and .

In order to fabricate the porous Mo with controlled pore characteristics, unique processing by using powder as the source and camphene as the sublimable material is introduced. Camphene-based 15 vol% slurries, prepared by milling at with a small amount of dispersant, were frozen at . Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at , and sintered at for 1 h. After heat treatment in hydrogen atmosphere, powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores due to the difference in the camphene growth rate during freezing process. The size of small pores was decreased with increase in sintering temperature, while that of large pores was unchanged. The results are strongly suggested that the porous metal with required pore characteristics can be successfully fabricated by freeze-drying process using metal oxide powders.

Dependence of the freeze-drying process condition on microstructure of porous W and pore formation mechanism were studied. Camphene slurries with contents of 10 vol% were prepared by milling at with a small amount of dispersant. Freezing of a slurry was done in Teflon cylinder attached to a copper bottom plate cooled at . Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at for 30 min, and sintered in the furnace at for 1 h. After heat treatment in hydrogen atmosphere, powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores with dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry.

An attempt was made to evaluate creep reliability of two commercial Ni-based superalloys by using ultrasonic wave. The materials include fine-grained PM alloy fabricated by mechanical alloying and subsequent hot isostatic pressing, and IN738LC cast alloy with a grain size of a few cm. Microstructural parameters (fraction of creep cavity and size of precipitates) and ultrasonic parameters (velocity, attenuation) were measured to try to find relationships between them. Ultrasonic velocity decreased with creep cavity formation in PM alloy. On the other hand, no distinct changing trend of ultrasonic velocity was observed for IN738LC alloy. Ultrasonic attenuation was found to have a linear correlation with the size of precipitates and was suggested as a potential parameter for monitoring creep reliability of IN738LC alloy.

In order to fabricate the porous metal with controlled pore characteristics, unique processing by using metal oxide powder as the source and camphene as the sublimable material is introduced. CuO powder was selected as the source for the formation of Cu metal via hydrogen reduction. Camphene-based CuO slurry, prepared by milling at with a small amount of dispersant, was frozen at . Pores were generated subsequently by sublimation of the camphene. The green body was hydrogen-reduced at for 30 min, and sintered at for 1 h. Microstructural analysis revealed that the sintered Cu showed aligned large pore channels parallel to the camphene growth direction, and fine pores are formed around the large pore. Also, it showed that the pore size was controllable by the slurry concentration.

The pressureless sintering behavior of /Cu powder mixtures, prepared from /CuO and /Cu-nitrate, has been investigated. Microstructural observation revealed that powders with nano-sized Cu particles could be synthesized by hydrogen reduction method. The specimens, pressureless-sintered at for 4 min using infrared heating furnace with the heating rate of /min, showed the relative density of above 90%. Maximum hardness of 16.1 GPa was obtained in /MgO/Cu nanocomposites. The nanocomposites exhibited the enhanced fracture toughness of 4.3-5.7 , compared with monolithic . The mechanical properties were discussed in terms of microstructural characteristics

The calcination and hydrogen-reduction behavior of Fe- and Ni-nitrate have been investigated. /NiO composite powders were prepared by chemical solution mixing of Fe- and Ni-nitrate and calcination at for 2 h. The calcined powders were hydrogen-reduced at for 30 min. The calcination and hydrogen-reduction behavior of Fe- and Ni-nitrate were analyzed by TG in air and hydrogen atmosphere, respectively. TG and XRD analysis for hydrogen-reduced powders revealed that the /NiO phase transformed to phase at the temperature of . The activation energy for the hydrogen reduction, evaluated by Kissinger method, was measured as 83.0 kJ/mol.

The effect of Cu content on microstructure and mechanical properties of nano-sized Cu dispersed nanocomposites was investigated. The nanocomposites with Cu content of 2.5 to were prepared by reduction and hot-pressing of powder mixtures. The nanocomposites with Cu content of 2.5 and exhibited the maximum fracture strength of 820MPa and enhanced toughness compared with monolithic . The strengthening was mainly attributed to the refinement of matrix grains. The toughening mechanism was discussed by the observed microstructural feature based on crack bridging

In-situ processing route was adopted to disperse carbon nanotubes (CNTs) into powders homogeneously. The composite powders with homogeneous dispersion of CNTs could be synthesized by a catalytic route for in-situ formation of CNTs on nano-sized Fe dispersed powders. CNTs/Fe/ nanopowders were densified by spark plasma sintering (SPS). The hardness and bending strength as well as electrical conductivity increased with increasing sintering temperature. However, the electrical conductivity of the composites sintered at above showed decreased value with increasing sintering temperature due to the oxidation of CNTs

An optimum route to synthesize composite powders with homogeneous dispersion of carbon nanotubes (CNTs) was investigated. nanocomposite powders were fabricated by thermal chemical vapor deposition of gas over nanocomposite catalyst prepared by selective reduction of metal powders. The FT-Raman spectroscopy analysis revealed that the CNTs have single- and multi-walled structure. The CNTs with the diameter of 25-43 nm were homogeneously distributed in the powders, and their characteristics were strongly affected by a kind of metal catalyst and catalyst size. The experimental results show that the composite powder with required size and dispersion of CNTs can be realized by control of synthesis condition

The microstructure and mechanical property of hot-pressed composites with a different temperature for atmosphere changing from H to Ar have been studied. When atmosphere-changed from H to Ar gas at 145, the hot-pressed composite was characterized by inhomogeneous microstructure and low fracture strength. On the contrary, when atmosphere-changed at low temperature of 110 the composite showed more homogeneous microstructure, higher fracture strength and smaller deviation in strength. Based on the thermodynamic consideration and microstructural analysis, it was interpreted that the Cu wetting behavior relating to the formation of CuAlO is probably responsible for strong dependence of microstructure on atmosphere changing temperature. The reason for a strong sensitivity of fracture strength and especially of its deviation to atmosphere changing temperature was explained by the microstructural inhomogeneity and by the role of CuAlO phase on the interfacial bonding strength.

An optimum route to fabricate the ferrous alloy dispersed nanocomposites such as /Fe-Ni and /Fe-Co with sound microstructure and desired properties was investigated. The composites were fabricated by the sintering of powder mixtures of and nano-sized ferrous alloy, in which the alloy was prepared by solution-chemistry routes using metal nitrates powders and a subsequent hydorgen reduction process. Microstructural observation of reduced powder mixture revealed that the Fe-Ni or Fe-Co alloy particles of about 20 nm in size homogeneously surrounded , forming nanocomposite powder. The sintered /Fe-Ni composite showed the formation of Fe phase, while the reaction phases were not observed in /Fe-Co composite. Hot-pressed /Fe-Ni composite showed improved mechanical properties and magnetic response. The properties are discussed in terms of microstructural characteristics such as the distribution and size of alloy particles.

In purpose of introducing the inverse magnetostrictive properties into the structural ceramics, based nanocomposites dispersed with nano-sized Ni-Co particles were studied. The composites were fabricated by the hydrogen reduction and hot-pressing of and NiO-CoO mixed powders. The mixtures were prepared by using Ni- and Co-nitrate as source materials for the Ni-Co particles. Microstructural observations revealed that nano-sized Ni-Co particles were dispersed homogeneously at grain boundaries. High strength above 1 GPa was obtained for the wt% Ni-Co nanocomposite fabricated by a controlled powder preparation process. The inverse magnetostrictive response to applied stress was obtained due to the presence of dispersed Ni-Co particles, which indicates a possibility to incorporate new functions into the structural ceramics without loosing the mechanical properties.