Fabrication of lotus-type porous metals through thermal decomposition of compounds

Lotus-type porous metals with directional pores are fabricated by unidirectional solidification in a pressurized hydrogen gas called as High Pressure Method (HPM). The pores are evolved when the gas atoms dissolved into the melt from the gas atmosphere are precipitated in the solidification process. However, this method has two obstacles for mass-production of the lotus metals; hydrogen is flammable and explosive when a small amount of oxygen is mixed in the chamber, and the use of high-pressure chamber is expensive and its handling is laborious. In order to overcome those shortcomings, we developed a novel method called as "Thermal Decomposition Method (TDM)" of compounds involving gas elements. During the solidification the gas pores are evolved in the same way as HPM. Moreover, when the compounds are decomposed in the melt, the metallic elements form some different compounds in the melt which serves as nucleation sites to evolve the fine pores with more uniform distribution. The fabrication method is superior to the conventional HPM.