Fabrication of Porous Steels via Space Holder Technique and Their Mechanical Properties

Porous metals, which include small pores inside metals, are promising materials due to their material and structural characteristics. Although they generally exhibit low strength because the pores behave as defects, porous metals are expected to achieve high specific strength due to their ultra-lightweight characteristic. This paper deals with a feasibility study on the fabrication of porous steels for developing unique metals with a high specific strength. Porous steels were fabricated via powder metallurgy-based space holder technique. Alloy tool steel, SKD11, and sodium chloride, NaCl, were used as a scaffold metal and spacer material, respectively. Mixed powders of SKD11 and NaCl were sintered via the spark plasma sintering technique. Each sintered compact was re-heated in an argon atmosphere to remove NaCl and densify the scaffold in the compact. Then, each compact was quenched and tempered. As a result, open-cell porous steels with porosities of 60% and 70% were successfully fabricated. The heat treatment refined the microstructure of the scaffold without changing the pore shape, porosity, etc., improving their strength property, irrespective of their porosity. Furthermore, the specific proof strength of heat-treated porous steels was comparable to that of dense pure aluminum.