Elemental aluminum powders and elemental titanium powders were ball-milled to fabricate Ti/Al composite powders with different titanium to aluminum ratio using several kinds of organic solvents as a process controlling agent. The organic solvent was decomposed during milling and the carbon was incorporated in the composite powder. The carbon content of the composite powder depended on the kind of the organic solvent. The composite powders were low pressure plasma sprayed onto a steel substrate to produce coatings. The coatings deposited on a water cooled substrate were predominantly composed of a metastable Ti3Al phase that was supersaturated with carbon. Heat treatment of the coatings led to the decomposition of the Ti3Al phase to a TiAl phase and fine Ti2AlC. When the thermal spraying was carried out on a preheated substrate, the main constituent of the coatings was a stable TiAl phase and Ti2AlC was detected by X-ray diffraction. The as-sprayed coating possessed a high hardness. Fine Ti2AlC particles appeared after heat treatment of these coatings. The volume percentage of the Ti2AlC ranged from 4.9% to 15.3% depending on the coating composition.
A ceramic coating with super hydrophilicity characteristics (the contact angle θ=0°) was prepared by the thermal spraying technique using calcinations powders recovered from the waste dry batteries (IZC). Evaporation behavior and evaporation time of a water droplet for the IZC coatings on a mild steel substrate were examined. It was found that the water droplet did not show the Leidenfrost phenomenon on the IZC coatings surface, and the evaporation time remarkably shortened compared with those on the grinding or blasted surfaces of the mild steel substrate. On the other hand, the cooling speed in soaking the heated test piece in boiling water was examined. The cooling speed of the IZC coated substrate remarkably increases in the initial stage, since it changes from film boiling to nucleate boiling. These facts suggest that the IZC coatings are effective for improvement in the evaporation and cooling speed.
Thermal spraying technology has been used for the improvement of wear resistance, erosion resistance, heat resistance and corrosion resistance. Corrosion, wear and abrasion resistance of the substrate materials were significantly improved by the paint coatings. These organic paint coatings, however, did not endure high temperatures and did not adhere well. Modern high performance machinery parts subjected to the extremes of temperature and mechanical stress, needs surface protection against high temperature corrosive media, and mechanical wear and tear. Chromium carbide based materials are commonly used for high temperature wear applications. In this study, we treated Cr3C2-NiCr coatings by laser irradiation treatment and examined its hardness in comparison with that formed by HVOF process. Consequently, the average hardness of laser irradiated Cr3C2-NiCr coating was found out to be higher than that of HVOF coating. The laser-treated Cr3C2-35%NiCr coating further improved the solid particle erosion resistance by a factor of almost twice.
An aluminum bicrystal specimen with a twin boundary was deformed in tension to 20%. During the deformation, the specimen developed two different areas inhomogeneously deformed, which were the area with delta-shape along the boundary and the special band of secondary slip (SBSS) inside the component crystals. The misorientation angle between the component crystals changed from 49.0 degrees to 57.3 degrees along the boundary due to the piled-up dislocations. Two recrystallization mechanisms were recognized at two kinds of inhomogeneously deformed areas in annealing. The strain induced boundary migration (SIBM) nucleated at the inhomogeneously deformed area with delta-shape adjoining to the boundary. The SIBM resulted in the exchange of the component crystal orientations, because the high angle SIBM boundary invading the component crystal had much higher mobility than the original boundary with almost zero misorientation. Recrystallized grains with island-shape were observed at the SBSS. The crystal orientations did not correspond with those before and after the deformation. The present mechanism which generated the recrystallized orientations not in the deformation structure was considered to be an important recrystallization mechanism at low strain.
The impact welding of aluminum onto copper was carried out using a gas gun, and the mechanical properties of Al/Cu joint were investigated by tensile tests and micro hardness indentation tests. The bonding strength measured by tensile test decreased with increasing an impact velocity. The results of the tensile tests suggested that it was necessary to make a microscopic survey of the joint interface. Then, the inverse analysis with FEM analysis was applied to the load versus depth curves measured by the indentation technique to identify the material constants in the constitutive equations of aluminum, copper and the compound layer. In addition, the numerical simulation for the tensile test was carried out using the identified material constants of aluminum, copper and the compound layer. The nominal stress-strain curve of the compound layer obtained by the numerical simulation showed the typical feature of brittle materials. The ultimate tensile stress of the compound layer was calculated to be about 1.4 GPa and ten times larger than that of aluminum. It was concluded that the bonding strength of Al/Cu joint was dependent on the integrity of the compound layer.