Solid State Phenomena Vol. 135

Abstract: A change of the mechanical property and microstructure of an Fe ion irradiated polycrystalline Fe-9wt%Cr model alloy to 1 dpa was examined using a nano-indentation and transmission electron microscopy. We anticipated that irradiated damage would be formed up to about 2.5μm and a displacement damage peak would be located at around 1.7μm from a surface through a TRIM code calculation. A thick dark band was formed at about 1.5μm from a surface with an actual TEM observation, which is consistent with a displacement damage peak in the TRIM code calculation. TEM observations showed that small defects with a Burgers vector a0<100> and 1/2a0<110> are formed in irradiated Fe-9wt%Cr alloy. In the nano indentation test, the hardness increase due to irradiation induced defects was up to 0.6GPa which can be converted to a yield stress increase of 200MPa.

Abstract: NiFe2O4 nano particles were synthesized by a simple levitational gas condensation (LGC) using Ni and Fe metal powder as starting materials. The TEM image reveals spherical particles with the range of the particle size from 8 to 22 nm. The Mössbauer spectrum revealed the presence of superparamagnetic phase with abnormal ionic states of Fe2+ and Fe3+

Abstract: In the present work, corrosion characteristics of ceramic dispersion strengthened (CDS) high-Cr stainless steel (SS) has been investigated. For the preparation of CDS SS with uniformly distributed reinforcements, TiC particles were mechanically activated with Cu powder by using high-energy ball mill machine, and then Cu-coated TiC particles were mixed with molten SS. Potentiodynamic polarization curves were experimentally measured on unmodified SS and CDS SS in 0.05 M NaCl solution. The values of corrosion potential Ecorr, corrosion current io, pitting potential Epit and polarization resistance Rp were quantitatively determined from the measured potentiodynamic polarization curves. From the result, it is concluded that CDS SS exhibits higher corrosion resistivity than unmodified SS.

Abstract: The microstructure and mechanical properties of Ti joints brazed with a Zr41.2Ti13.8Ni10.0Cu12.5Be22.5 (at.%) amorphous filler were investigated. With a Zr-based amorphous filler, in this study, Ti joints with a homogeneous composition could be obtained by heating to well below the α-β transformation temperature for a short time, so that the undesirable effects of the high temperature heating are considerably diminished. The joints brazed at 790 °C for 10 min consisted of the coarse acicular structure rather than the fine Widmanstätten structure which generally deteriorates the ductility of the joints. The joints with the homogenous coarse acicular structure, i.e. without a residual liquid region, show almost the same mechanical properties as those required for base metals without heating. Although the residual liquid region in the joints deteriorates the ductility of the joints, this region could be successfully removed by a diminution in the quantity of the filler.

Abstract: In this study, joining characteristics of dissimilar Ti and Cu metals have been investigated, when using both an Ag-based eutectic alloy as a filler and an Ag layer present on Ti base metal as a diffusion barrier. The observed microstructures were classified into three characteristic types, depending on the presence of a Ag layer at the Ti interface, e.g. first, the sample retaining thick continuous intermetallic layers, e.g. Ti2Cu, TiCu, Ti3Cu4, Ti2Cu3, and TiCu4 by a significant dissolution of the Ti atoms into the molten filler, in the absence of a Ag coating layer onto the Ti base metal, second, the sample with relatively thin Ti-Cu intermetallic layers by the reduced reaction of Ti with Cu due to a prominent decrease in the Ti dissolution, owing to the role of the Ag coating layer as a diffusion barrier, and finally, the sample without any brittle Ti-Cu intermetallics in the joint by a complete suppression of both the dissolution of the Ti atoms and its reaction with the Cu elements in the molten filler due to the presence of a Ag layer.

Abstract: Effect of magnesium addition on rapid transformation of α-alumina prepared from route of ammonium aluminum carbonate hydroxide during thermal heating and microwave radiation heating was investigated. The phase transformation and the final particle size of the transient alumina composite powder were significantly affected by amount of magnesium added in the aluminum precursor during the microwave radiation heating in various environmental atmospheres. Rapid transformation from γ- to α-phase was found in the magnesium added transient alumina by microwave-assisted transformation and nano-sized α-alumina was obtained. When the 3 wt% magnesium added ammonium aluminum carbonate hydroxide was heated by microwave radiation under nitrogen atmosphere, the transformation temperature from γ- to α-alumina was considerably lowered to 1000°C and the average particle size of 27.6 nm was attained for the α-alumina-spinel composite powder.

Abstract: The reduction behavior of WO3 and CuO powder mixture has been studied by using thermo-gravimetric(TG), X-ray diffraction, and scanning electron microscopic analyses. The powder mixture was manufactured by ball-milling. It was found that W coated W-Cu composite powders were formed when reducing the powder mixture under hydrogen atmosphere. The following reduction steps are suggested as a mechanism for the formation of W coated W-Cu composite powders: with increasing temperature, Cu is initially reduced from CuO and the reduction reactions of WO3 to WO2 via WO2.9 and WO2.72 are followed. The gas phase WO2(OH)2 is formed by the reaction of the WO2 and water vapor, and then WO2(OH)2 diffuses toward Cu surface and deposits on it as W by reducing reaction with environmental hydrogen gas. The formation mechanism of W coated W-Cu composite powders involving the gas phase transportation reaction has been confirmed by the model experiment conducted by using Cu plate and WO3 powder.

Abstract: Metallic and ceramic foam catalyst supports and catalysts were manufactured. Comparative studies of the foam-structure catalyst supports and straight-channel catalysts supports were performed. Affect of the catalyst support pore structure upon the catalyst operational performance was analyzed.