Unique microstructure of porous NiAl intermetallic compound prepared by combustion synthesis

Porous NiAl intermetallic compounds have been prepared by combustion synthesis from nickel and aluminum elemental powders. The synthesis process, pore structure and pore forming mechanism were studied systematically. The results show that porous intermetallic compounds are composed of single NiAl phase, which have unique feature of complex pore structure, i.e. micro-pores are distributed in the wall of macro-pores and small pores. It has been found that different pores are formed in different stages. The macro-pores are formed by the volatilization of pore-forming agent at preheating stage. Due to the kirkendall effect and molten Al to cover the surface of Ni particles by capillary force, small pores are formed during the reaction. The shape and the size of small pores depend largely on the Al particles. However, the formation of micro-pores in the unique complex pore structure mainly contributes to the liquid of Al and part of NiAl accompanied by liquid–solid reaction of Ni–Al at the cooling stage, which is different from the kirkendall pores.