Fabrication, Properties and Applications of Porous Metals with Directional Pores

Abstract

Porous metals with long cylindrical pores aligned in one direction are fabricated by unidirectional solidification through pressurized gas method (PGM) and thermal decomposition method of gas compounds (TDM). The pores are evolved from insoluble gas when the molten metal dissolving the gas is solidified in the dissolving gas (PGM) or inert gas (TDM). Three fabrication techniques, mold casting, continuous zone melting and continuous casting techniques, are adopted. The latter two techniques can control the solidification velocity and the last one possesses a merit for mass production of lotus metals. The porosity, pore diameter and its length are able to be controlled by the solidification velocity and ambient gas pressure, while the pore direction can be controlled by the solidification direction. Anisotropy in the elastic and mechanical properties is resulted from anisotropic pore morphology. The anisotropic behaviors of tensile, compressive and fatigue strength are explained in terms of the dependence of stress concentration on the pore orientation. The anisotropic properties of thermal, electrical conduction and magnetization are also found, which are attributed to the scattering of heat flux, electric current and magnetic flux with anisotropic pores, respectively. Several applications of the porous metals to manufacturing products are investigated. The unidirectional pores can be utilized for high performance of heat sinks for electronic devices of cars and computers. Thus, the porous metals are expected to be used for various manufacturing products.