Fabrication of lotus-type porous metals and their physical properties

Lotus-type porous metals whose long cylindrical pores are aligned in one direction were fabricated by unidirectional solidification in a pressurized gas atmosphere. The pores are formed as a results of precipitation of supersaturated gas when liquid metal is solidified. The lotus-type porous metals with homogeneous size and porosity of the evolved pores produced by a mould casting technique are limited to the metals with high thermal conductivity. On the other hand, the pores with inhomogeneous pore size and porosity are evolved for metals and alloys with low thermal conductivity such as stainless steel. In order to obtain uniform pore size and porosity, a new "continuous zone melting technique" was developed to fabricate long rod- and plate-shape porous metals and alloys even with low thermal conductivity. Mechanical properties of tensile and compressive strength of lotus-type porous metals and alloys are described together with internal friction, elasticity, thermal conductivity and sound absorption characteristics. All the physical properties exhibit significant anisotropy. Lotus-type porous iron fabricated using pressurized nitrogen gas instead of hydrogen exhibits superior strength.