Nanocrystalline nickel dispersed with nano-size WO3 particles has been successfully synthesized using electrodeposition. In this synthesis, ionized WO4 2− molecules in an electrolyte are hydrolyzed WO3 particles and embedded into a nanocrystalline nickel matrix during electrodeposition by controlling the pH and potential of the electrode. The effect of the nano-size WO3 dispersions on the mechanical property and thermal stability of the nanocrystalline nickel is investigated in detail. The nanocrystalline nickel electrodeposited with nano WO3 particles have the same size as the nickel matrix of approximately 25 nm and the dispersed WO3 particles which is approximately 15 nm. The nickel electrodeposited with the WO3 particles has a higher hardness than that without the WO3 particles in the range of the nickel matrix grain size which is less than about 130 nm. The increase in the hardness is attributed to dispersion strengthening of nano WO3 particles. The nickel electrodeposits with the WO3 particles possess an increased thermal stability compared to the material without the WO3 particles. The nickel matrix grain size of electrodeposits associated with the WO3 particles hardly changed even after annealing for 18 ks at 573 K. The thermal stability of the nickel electrodeposits with the WO3 particles is attributed to the Zener drag effect of nano the WO3 particle.
The effect of a fine particle peening (FPP) on atmospheric oxidation behavior and tribological properties of Ti-6Al-4V alloy was evaluated. Surface microstructures of oxidized specimens pre-treated with FPP were characterized using scanning electron microscope (SEM), energy dispersive spectrometry (EDS), glow discharge optical emission spectrometry (GDOES) and X-ray diffraction (XRD). The oxide layer formed on the oxidized specimen pre-treated with FPP was thicker than that on the oxidized-only specimen, because the microstructure induced by FPP facilitated the diffusion of oxygen and aluminum elements during the oxidation process. As results of reciprocating sliding wear tests, width of wear track on the oxidized specimen pre-treated with FPP was shallower compared to the oxidized-only specimen. Moreover, the oxide layer formed at the oxidized-only surface was delaminated during tests, otherwise there was no delamination at the oxidized surface pre-treated with FPP. This was because the surface oxide layer exhibited good interface adherence due to the existence of a thick oxygen solid solution layer. These results indicate that the modified layer created by the combination process of FPP and atmospheric oxidation is effective to improve the wear resistance of titanium alloys.
The effect of oxidation accelerated by ammonium sulfate prior to annealing on galvannealing time of Si-bearing galvanized steel has been investigated to develop a new process for manufacturing Si-bearing galvannealed steel. Oxidation accelerated by ammonium sulfate prior to annealing was effective to shorten the galvannealing time of the steel. The steel treated with ammonium sulfate showed the same galvannealing time as mild steel under the conventional oxidation condition. This is probably due to not only the suppression of the formation of external oxides, which suppressed the Fe/Zn reaction during galvannealing but also the penetration of zinc into the grain boundaries and the reduced iron layer/the steel interface during galvanizing.
Recent study demonstrated that processing through High-Pressure Sliding (HPS) is effective for grain refinement of a rod-like A2024 aluminum alloy. In this study, the HPS processing was applied to an AZ61 magnesium alloy. To achieve homogeneous grain refinement throughout the cross section of the rods, the samples were rotated around the longitudinal axis of the rod every after HPS processing. Microstructural observations revealed that the grain size was refined to 450 nm. Tensile tests showed that the samples exhibited excellent superplasticity with a maximum elongation of 1140% at a testing temperature of 473 K and at an initial strain rate of 1.0×10−3 s−1, giving a strain rate sensitivity of 0.4.
Two pure aluminum foams were bonded using foaming of a low melting point precursor and the bonding strength was evaluated. Two rectangular pure aluminum foams with about 77% porosity was obtained by a precursor method. The commercial flux was applied to the bonding areas of pure aluminum foams. The low melting point precursor sheet manufactured from ADC12 aluminum alloy was put between the pure aluminum foams and was fixed in the stainless steel square tube. The specimen was heated in a muffle furnace. The four point bending test was carried out for the bonded specimen. Some bonded specimens were broken in the matrix. The flexure strength of the bonded specimen varies widely. This is because that a part of the cell walls of the bonded area was melted and broken.
Previously we have reported that dislocation cells which are formed by cold-rolling grew into recrystallized grains with other dislocation cells formed via the recovery of microstructures. There are not any differences between these cells after deformation and similar microstructural changes would occur in both cell types at an early stage of annealing. Intermittent observations via SEM-EBSD were performed during annealing on the same areas in the specimens of 1050 aluminum cold-rolled at 28, 45 and 73% and then annealed at 673 K. Dislocation cells were formed in all the specimens except in an area of the specimen cold-rolled at 28% in which dislocation tangles were formed. These tangles did not migrate or anneal out. Changes in the microstructure did not occur in area of annealing, and recrystallized grains which were formed through the SIBM mechanism invaded the area. In the specimen cold-rolled at 45%, dislocation cells with orientations that deviated from the circumference were observed, which shrank and disappeared at the early stage of annealing, resulting in formation of regions composed of sub-grains having a similar orientation. These sub-grains were surrounded with low angle boundaries and exhibited suppressed growth. In the case of the specimen cold-rolled at 73%, the orientation of the original grains split into two due to cold-rolling, and dislocation cells that had each orientation were formed via dispersion with each other. Dislocation cells grew into sub-grains, and sub-grain boundaries migrated with areas of low dislocation density forming. At this stage, the sub-grain was composed of areas with low and high dislocation densities. The latter was invaded by other sub-grains via subgrain boundary migration, and the remaining area that had a low dislocation density being surrounded by high angle boundaries formed a recrystallized grain. This effect was due to the neighboring sub-grains having other orientations. Growth of dislocation cells into recrystallized grains depends on misorientation between the neighboring grains.
Electrodeposition of Zn-Zr oxide composite was examined from an unagitated sulfate solution containing Zn2+ and Zr ions at pH 1 to 2 and 313 K under galvanostatic conditions. Zr content in deposits was higher in pH 2 than that in pH 1, and decreased for the moment with increasing current density, but the further increase in current density brought about the increase in Zr content in deposits. This increase in Zr content in deposits is attributed to the acceleration of the hydrolysis of Zr ions by means of an increase in hydrogen evolution in the cathode layer. In solution containing Zr ions, Zn deposition was significantly polarized due to the film resistance of Zr oxide formed by the hydrolysis of Zr ions. The pH in the vicinity of the cathode, as measured by an Sb microelectrode, was approximately 2.2, which is close to the critical pH for the formation of ZrO2. SEM and EDX point analysis of deposits revealed that the granular Zr oxide deposited at the surface of Zn platelet crystals and at the void between the Zn platelet crystals. It was found from the polarization curves in 3 mass% NaCl solution that the corrosion potential of deposited Zn-1.1 mass% Zr oxide films was more noble than that of pure Zn, and the corrosion current density of Zn-1.1 mass% Zr oxide films was lower than that of pure Zn.
Polyaniline films were formed on an Fe substrate using the oxidative electropolymerization technique at 288 K in aqueous solutions of pH 2 to 10 containing aniline and p-toluenesulfonic and oxalic acids as supporting electrolytes, and the effect of conditions of electrolysis on the morphology and corrosion resistance of the films was investigated. Although the polyaniline films were formed partially in solutions of pH 2 to 4, the formation of films completed and the surface became smooth in solutions of pH 7 to 10. Polyaniline films with a smooth surface and good corrosion resistance were obtained at 8 to 30 A•m−2, while the films obtained at current densities above 50 A•m−2 showed a non-uniform surface morphology and the insufficient corrosion resistance. Films obtained at anode potentials of 0.4 and 0.8 V vs. NHE were not formed completely, and the films formed at an anode potential of 2.0 V exhibited very rough surfaces. Films formed from the solution containing p-toluenesulfonic acid as a supporting electrolyte exfoliated from the Fe substrate following immersion in a 3 mass% NaCl solution for 3 h. Although the films obtained from the solution containing oxalic acid as a supporting electrolyte showed the good adhesion to the substrate, they possessed many defects and pores, and as a result, the improvement in the Fe's corrosion resistance was less. In the solution containing both p-toluenesulfonic and oxalic acids as supporting electrolytes, the Fe coated with polyaniline films showed the good improvements in both corrosion resistance and adhesion.