Effect of Pore Size on the High Temperature Oxidation of Ni-Fe-Cr-Al Porous Metal

This study investigated the effect of the pore size of Ni-22.4% Fe-22% Cr-6% Al porous metal on its high-temperature oxidation. Two types of open porous metals with pore sizes of 800 mu m and 580 mu m were used. A 24-hour isothermal oxidation test was conducted at three different temperatures of 900 degrees C, 1000 degrees C, and 1100 degrees C under a 79% N-2 + 21% O-2 atmosphere. The results of the BET analysis revealed that the specific surface area increased as the pore size decreased from 800 mu m to 580 mu m. The high-temperature oxidation results showed that porous metals exhibited far lower levels of oxidation resistance compared with bulk metals, and that the oxidation resistance of porous metals decreased with a decreasing pore size. According to the microstructural observations of the oxide layers, the 900 degrees C and 1000 degrees C oxidation layer contained Ni, Cr, and Al oxides mainly on the strut. The 800 mu m porous metal strut exhibited similar oxidation behavior at 1100 degrees C to that found at lower temperatures. In contrast, the 580 mu m porous metal strut was found to consist of Ni and Fe oxides in the upper layer and Ni, Cr, and Al oxides in the lower layer, representing a low oxidation resistance. For powders affixed to the strut inside the porous metal, a different oxide-forming behavior from that of the strut was observed. In addition, the Ni-Fe-Cr-Al porous metal high-temperature oxidation microscopic mechanism is also discussed.