In our previous study, high strength brass pipes were fabricated by the centrifugal casting with machining chips. It was found that the obtained centrifugal casts have smaller microstructures. This study was carried out to discuss the origin of the refined microstructure. For this purpose, α and β brass machining chips and molten α brass where primary crystal was α phase and α+β brass where primary crystal was β phase were used, and systematical casting experiments were carried out. It was found that the grain sizes of α and β matrix casts with α and β brass machining chips, respectively, were smaller than those of α and β matrix casts with β and α brass machining chips, respectively. These results can be explained by disregistry value between machining chip phase and primary crystal phase.
Closed-cell Zn-22Al superplastic alloy foams were manufactured through the melt foaming process. The Zn-22Al foams were produced with varying porosity of 51-82%. The cell wall consisted of fine equiaxial crystal grains after solution treatment. The compressive properties of the Zn-22Al foams were investigated at 523 and 298 K. The Zn-22Al foams have strain rate sensitivity exponent of 0.55 in Region II. This is because of the superplastic deformation induced by the fine microstructure of the cell wall. High temperature deformation mechanism can be explained using the new parameter of local strain rate. We developed new constitutive equation of metal foam including relative density, local strain rate and strain rate sensitivity exponent.
The effect of surface-treatment on the plain fatigue and fretting fatigue behaviors of Ti-6Al-4V was investigated using specimens subjected to four processes/treatments: surface polishing (A), polishing followed by shot peening (A-SP), carbon-doped oxidation (B) and carbon-doped oxidation followed by shot peening (B-SP). B-SP-treated specimens showed the highest fretting fatigue limit for B-treated fretting pad, and the A-treated specimens showed the highest plain fatigue limit. These results are discussed considering surface conditions, residual stresses and fractographic details as induced by the surface treatments. It was found that the compressive residual stresses and the hardness of the region near the specimen surface had a large effect on fatigue behavior.
Layered structure of indium zinc oxide (IZO) films sputter deposited on a (001) sapphire substrate at temperatures of 673 and 873 K was investigated by electron microscopy. IZO films were grown epitaxially in  direction on a sapphire substrate. Lattice distances of a deposited IZO film were close to those of an In2ZnkOk+3 compound estimated from In-Zn ratio of the film. Periodical layered structure was observed in the films of k=1, 2, and 3, when the substrate temperature was 873 K. Crystal structure and lattice parameters of the compound of k=1, In2ZnO4 was determined as a=0.3392 nm, c=2.627 nm with the rhombohedral structure.
Viscosity of supercooled liquids and thermal properties in Zr55+xCu30−x−yNi5+yAl10 (x=0, 5, 10, y=0, 2, 5, 10) (at%) bulk metallic glasses (BMGs) have been examined. Viscosity has been measured by using a penetration viscometer at a high speed heating rate of 6.67 K/s in a high purity He-gas atmosphere. With the increase of the Zr-content from 55 to 60 at% and above, the viscosity of the supercooled liquids was drastically decreased from roughly η=108 to 107 Pa•s at 750 K. In this case, the glass transition temperature (Tg) was slightly decreased and the crystallization temperature (Tx) was largely increased due to the change of the main crystallization phase from metastable fcc-Zr2Ni to stable bct-Zr2Cu, resulting in a large increase of the ΔTx (=Tx−Tg) value. Maximum ΔTx values of 128 K and 172 K were observed in the Zr65Cu18Ni7Al10 BMG at heating rates of 0.67 and 6.67 K/s, respectively. It may be suggested that the drastic change of the viscosity and the main crystallization phase may be due to the structure change of the supercooled liquids in the compositional border between 55 and 60 at% Zr.
Urchin structured nickel fine particles have been successfully obtained by the hydrazine reduction of NiCl2•6H2O in ethanol. Changing the time of the addition of hydrazine and sodium hydroxide can control the particle structures, especially the aspect ratio of the Ni nanoneedles. These particles were not stabilized by organic compounds. In-situ TEM observation at high temperature revealed the deformation of the obtained fine particles began at 350℃.