Al₂O₃/Al composites manufactured by in-situ reaction between molten Al and SiO₂ were investigated. Near net shape composites were obtained after the reaction. The effects of molten Al temperature and dipping time on the reaction rate, density, and structure of the composites were investigated. The maximum reaction rate of approximately 1.1 mm/ks was obtained in molten Al at 1138 K and 1473 K. When a SiO₂ rod is dipped in molten Al at 1273 K and above, the density is 3.5 Mg/m³ and the hardness is 300-330 HV. Intermediate layers can be observed between the layer where the reaction occurred and the SiO₂, which incurred no reaction. The hardness of the intermediate layer is about 660HV10, and the structure of this layer is composed mainly of fine Al₂O₃. This composite material is composed of continuous Al₂O₃. Al, and a small amount of Si. The volume fraction of Al₂O₃ is approximately 70%, while the remainder is Al-Si alloy. In order to stabilize the layer where the reaction occurs, the temperature of the molten Al should be preferably above 1273 K.

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  A computer model was developed to establish the relations between 2-dimensional (2D) and 3-dimensional (3D) parameters such as number of particles and particle size distribution. Computer experiments were performed for both monodispersed and lognormally polydispersed systems. The model is based on distributing a number of spherical grains randomly and without intersection between the grains in a cubic unit. The cubic unit was cut by a random plane and the number of particles which appear in the section and their area fraction were measured. This procedure was repeated so that the average number of particles and the average area fraction become constant. Finally, the 2D size distribution of the particles over all sections was obtained. As a result it was concluded that the volume fraction is equal to the area fraction irrelevant to particle size distribution providing that the total number of measured 2D particles is large enough. As for the number of particles, a relation was deduced to calculate the number of 3D particles in a monodispersed system depending on the number of 2D particles and the volume fraction. On the other hand, in lognormally polydispersed systems the number of 3D particles could be calculated in consideration of the 3D mean and the standard deviation which were estimated from the 2D mean and the standard by a method developed for this propose. Finally, the method was applied on two ductile cast iron specimens and the applicability of the present model was verified.

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  The effects of sulfur, titanium and zirconium on the shape of eutectic solidification front in gray cast iron were investigated by interrupting unidirectional solidification. The specimens contain 0.012, 0.108, 0.37mass%S, 0.177mass%Ti, 0.078mass%Zr respectively. They are 80 g in weight. 17mm in diameter. and 55mm in length. The temperature gradient at the solid-liquid interface is about 25 K/ cm. The oscillatory model for graphite branching is proposed by considering the shape of the solidification front and protuberance length of the graphite flakes.

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  It is important to simulate and control macro compositional segregation of alloyed elements, in order to produce large ingots for forging and VAR(Vacuum Arc Remelting) ingots with high quality and reliabilty. In this study, a simulation model which uses database for thermodynamic calculation, solidification analysis and material balance calculation by solute redistribution during solidification was developed and applied for large ingots made of 2.25 Cr-1Mo steel (190t), 3.5NiCrMoV steel (180t), 3.0NiCrMoV steel (420t) and Ti-Pd alloy VAR ingot. The calculated results proved to be in excellent agreement with the experimental results, and the simulation model was proved to be suitable for manufacturing.

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  In order to increase the wear resistance, spheroidal graphite cast irons with ferritic matrix were carburized and/or alloyed with tungsten by YAG laser-beam surface melting. Laser-treated iron without alloying elements has a hypo-eutectic chill structure with austenite dendrites. This micro structure can be changed to a hyper eutectic chill structure with primary cementites by laser carburization with graphite powder. Laser-treated iron with carburizing and tungsten alloying had hard WC carbide. The average hardness of a laser-treated iron without alloying elements, a carburized iron and iron both carburized and W alloyed were, 820 HV 0.1, 1100 HV 0.1 and 1150 HV 0.1 respectively. Pin on disc type tribo-tests revealed that these laser-treated irons have excellent wear resistances. This laser carburizing process could easily be applied to low carbon steel and 18 Cr-8Ni steel.

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  Influence of microstructure on the effect of laser beam surface hardening of spheroidal gphite cast iron was investigated. Cast irons with a bull’s eye structure and ferritic matrix were used to clarify the effect of matrix microstructure by laser treatment. At the same time, cast irons with different graphite nodule sizes were laser treated for the investigation of the effect of graphite size on melting behavior. Spheroidal graphite cast irons were coated by graphite powder and/or tungsten powder for YAG laser carburizing and/or tungsten alloying. Microscopic observations were carried out on the laser-treated surface layers. The surface layer of the cast irons formed into a chill structure by rapid melting and cooling with laser beam scanning. The melted depth of cast irons were varied with the microstructure and coatings. For example, the melted depth of ferritic matrix irons was deeper than that of bull’s eye cast irons. Moreover, the carbide fraction of chilled layers was varied with graphite nodule size.

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  Laser Cladding is the conventional techniques for metal surface coating to improve corrosion resistance and strength while retaining the properties of the base metal. In this study, Ni base alloy is coated on a carbon steel by using pulse YAG laser. To investigate the degree of fusion between the base metal and the coating material, the depth and width of fusion of the base metal is calculated by using the finite element method for heat conduction. By comparing the calculated results with the experimental result, it is found that the depth and width of fusion can be predicted by the simulation. The depth of fusion increases as the peak power of pulse radiation increases, and is doubled by preheating the base metal from room temperature to 731 K. By increasing the degree of fusion, the adhesiveness between the base metal and coated metal is heightened but the hardness of the clad part is lowered.

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