Fabrication of porous NiAl intermetallic compounds with a hierarchical open-cell structure by combustion synthesis reaction and space holder method

We have developed a process to fabricate porous NiAl intermetallic compounds with a bi-modal porous structure by combining the combustion synthesis reaction and the space holder method. The fabricated porous NiAl showed large pores of the order of several tens of micrometers derived from the NaCl space holder and small pores of the order of several micrometers derived from the combustion synthesis reaction. The NaCl space holder acted as a heat absorber and contributed to the formation of small pores by preventing the melting of NiAl. Although the reaction was difficult to complete for large volume fractions of NaCl, it was possible to obtain single-phase NiAl by controlling the sintering conditions. We could finally obtain highly porous (porosity: >80%) single-phase NiAl with a hierarchical open-cell structure.