Fabrication of Lotus-type Porous Metals by Continuous Zone Melting and Continuous Casting Techniques

摘要

The mold casting technique cannot be applied to fabricate lotus-type porous metals and alloys with low thermal conductivity. When the bottom part of the mold is cooled, the melt is solidified fast near the bottom and slowly at the upper part. The solidification velocity in the unidirectional solidification is not constant so that the pore size and the porosity are not uniform. Lotus-type porous metals and alloys with homogeneous porosity and pore size were produced using "continuous zone melting technique" for the metals and alloys with low thermal conductivity such as stainless steel, carbon steel, Ni3Al intermetallic compounds and NiTi shape memory alloys. This technique has an advantage to control the solidification velocity regardless of the magnitude of thermal conductivity. When lotus-type porous metals are put to practical use, mass production is indispensable. However, previous methods like a casting technique are not suitable. Recently, we developed a new "continuous casting technique", by which long lotus-type porous plate or rod can be fabricated. The molten metal dissolving gas in a crucible is solidified continuously through cooled mold as being pulled down at a given velocity. The pore size can be controlled by the solidification velocity, although the porosity is not varied much. An increase of solidification velocity leads to a decrease of pore size and an increase of pore number density in the lotus-type porous copper.