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7091 Al alloy is high strength aluminum alloy and application of this alloy enlarge in current industry system. The powder of rapidly solidified 7091 Al alloy was produced by rapidly solidification processing(RSP). In this study, it was investigated the structures of rapidly solidified 7091 Al alloys ; powder morphology, growth shape, microstructure, particle collisions, satellites, cooling rate. Particle shape was more spherical as decreasing powder diameter, and SDAS was more narrow as decreasing powder diameter, therefore cooling rate was more increased. The effect of powder collision affected on the powder structures and shapes.

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The microstructure changes of rapidly solidified Al-Fe-Mo-Si alloys(Al-4Fe-0.5Mo-1.5-Si and Al-8Fe-2Mo-1.5Si) have been investigated by in -situ heating experiments at 450° and 500℃ in the transmission electron microscope. Both alloys contain two distinct regions : regions without solidification cell structure but with intergranular precipitates (A) and regions with intergranular precipitates (B) The fine nm-scale precipitates existing in Al-Fe-Mo-Si alloys coarsen during annealing. Intercellular precipitates in zone B of the Al-4Fe-0.5Mo-1.5Si alloy, which were initially of rod-like morphology, change into sphere-like particles after annealing for 10 minutes at 450℃. The precipitates in regions A and B are observed to obey an R³∝t kinetic relationship. On the other hand, the precipitates in Al-8Fe-2Mo-1.5Si alloy show no sign of coarsening at 450℃. At 500℃, however, the precipitates in the zone A of Al-8Fe-2Mo-1.5Si alloy coarsen slightly, but the precipitates in zone B do not coarsen appreciably.

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Characteristics of Cu-based shape memory alloy are high elastic anisotropy and large grain size. So their mechanical properties such as fracture strength, ductility and fatigue strength are low by intergranular fracture due to those characteristics, and they are worse available than Ti-Ni alloys in practical applications. In this work, the study of manufacturing process of Cu-Al-Ni alloy by powder metallurgy using HIP technology was carried out in order to improve the mechanical properties. According to this experiment, more increasing of hot rolled ratio became coarser in grain size. Although increasing of the temperature in solution treatment there was not changed in grain size. In spite of having larger grain size of the specimen by powder metallurgy than that of the specimen by ingot making method, the fracture strength and elongation were increased by 25∼60 % and 90∼110%, respectively.

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In this study, the effect of heat treatment and hot isostatic pressing (HIP) on the creep-rupture properties of IN 713 LC was investigated, with special attention paid to illustrate the role of carbides at 760℃/587㎫ creep. The rupture life after ageing treatment was increased with increasing temperature for solution heat- treatment and HIP, and with decreasing time for the given temperatures. HIP did not increase the creep-rupture properties, because the failure was governed mainly by the brittle grain boundary fracture. The variation of the creep-rupture life with exposure time at solution heat-treatment temperatures, 1176℃ and 1205℃, and at ageing temperatures, 926℃, was due to the irreversible change in the kinds and shapes of the carbides near grain boundaries.

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Among many metals magnesium has excellent hydrogen-storage characteristics except that its hydriding and dehydriding rates are low. Many works have been carried out in oredr to ameliorate the reaction rates of magnesium with hydrogen. However, their processes of the sample preparation were energy -consuming and complicated. In this work, to simplify the process of sample preparation, samples with a composition 2Mg + Fe were prepared only by mixing Mg and Fe. For these mixtures the following hydrogen-storage characteristics were investigated : formation of dimagnesium iron hydride, activation process for hydriding - dehydriding reaction, equilibrium plateau pressures, microstructure of the hydrided sample, life as a hydrogen - storage material, and hydriding and dehydriding rates.

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In order to evaluate the life of steam turbine blade, information of the crack initiation at corrosion pits and the crack growth is needed. Corrosion pits are made artificially on the specimens machined from the real turbine blades(12% Cr steel) and specimens are tested to study the small crack initiation and growth. Difference between the small cracks and the long cracks is made by the crack growth behavior and the size of small cracks is 700∼800㎛ equivalent to 14∼18 times of grain size. The formation fife of these small cracks reveals 80∼90% of total fatigue life and those life with smaller applied stress shows larger portion of total life than that of larger stress.

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High temperature(600℃) tensile properties and microstructure of Ni₃Al intermetallic compound made by either reactive sintering or hot extrusion using elemental powders were studied. The content of Al was varied within a range of 24 to 25 at.% to adjust the chemical stoichiometry and 0.1 wt.% of B was added to suppress the intergranular brittleness. In reactive sintering, rapid densification was achieved below 720 ℃ due to liquid phase formed during heating. The extrusion improved the density and the ambient and high temperature tensile properties of experimental alloys remarkably. The fracture characteristic was changed from intergranular to transgranular by B addition and the ductility was enhanced by reducing Al content from 25 at.% to 24 at.% in Ni₃Al-B alloy. The density and the elongation of hot extruded Ni₃Al- B alloy were 99% and 41%, respectively at room temperature and the yield strength was improved over those of ingot material or reactively sintered material by a factor of two.

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Size distribution of Al ultra fine particles (UFP) generated by evaporating Al vapor into low pressure Ar environment is studied with varied gas pressure, evaporation temperature, position of particle collection, and inert gas velocity. Particles are observed to be spherical irrespective of operating conditions, which shows that they are formed by homogeneous nucleation process and the size distribution is very close to log -nomal. The mean size increases with increased pressure, temperature and the distance to collection and reduced gas whereas the standard deviation decreases with increased gas velocity and temperature.

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An in-situ electron microscope study has been conducted to characterize the fracture and crack tip deformation behavior of metals under tensile and cyclic loading in a transmission electron microscope (TEM). The results show a number of new findings regarding the dislocation behavior near the tip and its relationship to the mode of crack propagation. Dislocation emission at the crack tip was found to depend strongly on the geometry of plastic zone, which contains a dislocation-free-zone(DFZ) just ahead of the crack tip. The difficulty of dislocation emission was, in turn, manifested by the fracture toughness. These experimental results were then compared to the theoretical analysis based on the DFZ model of fracture. Furthermore, this in-situ method has been extended to study the cyclic loading on the behavior of crack-tip-generated dislocations. It is found that dislocations emitted from a crack tip during tensile loading can be retracted and annihilated partially upon unloading. The change of plastic zone, dislocation distribution, and the DFZ during the retraction process were carefully examined using a TV/video camera. Their consequent impact on the crack propagation were then discussed in connection with the previously proposed dislocation theory of fracture and dislocation shielding for a moving crack.

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The effects of various factors on the oxidation reactions of As(Ⅲ) in HNO₃, solution were investigated. The oxidation rate of As(Ⅲ) was increased with the addition of HCl as a catalyst and also with the formation of NO₂ gas, while it was decreased with the addition of O₂ due to the expulsion of NO₂ gas dissolved in the solution. The oxidation rate of As(Ⅲ) in HNO₃ solution could be expressed as the following equation at 7N HNO₃ and 75℃ : - d〔As(Ⅲ)〕/dt=K〔HCI〕 {0.0277+0.0116 〔As(Ⅲ)_o-As(Ⅲ)〕^(0.5)} 〔As(Ⅲ)〕^(0.5).

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