Papers by Keyword: Lotus-Type Porous Metal

Abstract: A Ti coating was deposited on not only surface but also inner surface (pore wall) of a lotus-type porous copper with porosity of 43.3% and pore size of 603.5μm by arc air plating for modification. The structure, microhardness and compressive properties of the porous copper were investigated, and compared to those after annealing under 600°C and 800°C for 6 hours. It is indicated that Ti coating with thickness from 4.6μm to 12.5μm has been deposited on the pore wall for the porous copper successfully. It is found that the HV_0.01 increases from 89.32 to 348.19 for the porous copper after the deposition, which is attributed to the higher hardness of the Ti coating. In case of 0.2% yield stress, it keeps almost the same for the porous copper with the deposition of the Ti coating, while increases from 21.22 to 23.79MPa after annealing, which may stem from the improved adhesion of the coating with pore wall by diffusion. It is believed and much possible for metal coating to improve the mechanical properties of lotus-type porous metal.

Abstract: Lotus-type porous metal with many straight pores is attractive as a heat sink because larger heat transfer capacity is obtained due to the small diameter of the pores. The heat transfer capacity of the lotus-type porous copper heat sink was calculated using the model with the pores of uniform diameters. However, actual lotus-type porous metals have a distribution of pore diameter. In the present work, we investigated the lotus-type porous copper fin model by considering size distribution of the lotus-type porous copper fin. Prediction of the heat transfer characteristics for the lotus-type porous copper heat sink shows a good agreement with the experimental data.

Abstract: Lotus-type porous aluminum was fabricated by continuous casting technique in mixture gas of hydrogen and argon at various transfer velocities in order to understand formation process of pores. The porosity and pore diameter decrease with increasing transfer velocity. The transfer velocity dependence of the porosity in lotus aluminum is different from that in other lotus metals such as stainless steel and copper. It is considered that the difference is attributed to lower solubility in aluminum than that in other metals.

Abstract: Lotus-type porous magnesium ingots were fabricated in pressurized hydrogen atmosphere through a mold casting technique. The mold consists of two cooling blocks placed at the bottom and one lateral side. It was found that the pores started to grow upwards and horizontally and the both directional pores collapsed and then shifted to the direction. Such anisotropic growth of pores is in good agreement with the map of temperature gradient predicted by two-dimensional finite differential analysis.

Abstract: Lotus-type porous metals, whose pores are aligned in one direction by unidirectional solidification, have a unique combination of properties. These are expected as revolutionary engineering materials with anisotropy of the properties. For the industrial use of the lotus-type porous metals, a reliable joining technology is required. We already reported the melting property of a few lotus-type porous metals by laser welding. These results indicated that these materials possessed anisotropy of melting property with the pore direction perpendicular and parallel to the specimen surface, especially remarkable anisotropy was obtained for the copper specimen owing to the difference of the laser energy absorption to the specimen surface. In this report, the three-dimensional heat transfer analyses, which take into account the difference of the laser energy absorption comparing with the anisotropy of thermal conductivity inherent to lotus-type porous metals, were performed by commercial code with user-defined subroutine. Predicted profile of weld fusion zone is in good agreement with the cross-sectional view obtained by experiments.

Abstract: Lotus-type porous NiAl and Ni3Al intermetallic compounds, possessing cylindrical pores aligned in the direction parallel to the solidification direction, were fabricated by using a unidirectional solidification technique in a pressurized hydrogen atmosphere of 2.5MPa. The porosity of lotus NiAl is 24.2 %, and the porosity of lotus Ni3Al is 3.2%; the porosity of the porous NiAl is larger than that of Ni3Al. This is because the solubility gap of hydrogen between liquid and solid phases of NiAl is larger than that of Ni3Al.

Abstract: Lotus-type porous metals with low thermal conductivity are fabricated by continuous zone melting technique, which possess directional elongated pores. The porous metals have been able to be fabricated through the conventional casting method by utilizing the solubility gap between solid and liquid in pressurized gas atmosphere. However, there is a shortcoming that the pores are coarsened in the part farther from the chill plate in the ingot. In order to overcome such a shortcoming, we developed the continuous zone melting technique and successfully produced the lotus-type porous metals with even low thermal conductivity such as stainless steel and superalloys. Furthermore, from the viewpoint of mass production with low cost, we invented novel ”continuous casting technique”. The molten metals dissolving gas are solidified continuously by passing through the mold cooled with chiller and thus, lotus-type porous metal plate as long as one meter was produced for short time. Sufficient uniformity of the porosity and pore size was obtained in such long porous ingots. This technique is prospective method for commercial mass production.

Abstract: Effects of pore directions on the profile of fusion zone for lotus-type porous magnesium by laser welding has been investigated by comparing the experimental observations and the results of numerical simulation. The three-dimensional finite element calculations were performed, which takes into account equivalent thermal properties and anisotropy of thermal conductivity. There is the pore anisotropy in the profile of fusion zone by laser beam irradiation and the good weldability was obtained when the growth direction of the original pore equaled to the direction of the laser beam irradiation. A good agreement was obtained between the calculated profile of the weld fusion zone and the experimental results.