Journal of the American Ceramic Society, Vol.101, No.2, 542-552, 2018
High-temperature oxidation and compressive strength of Cr2AlC MAX phase foams with controlled porosity
Cr2AlC foams have been processed for the first time containing low (35vol%), intermediate (53vol%), and high (75vol%) content of porosity and three ranges of pore size, 90-180m, 180-250m, and 250-400m. Sacrificial template technique was used as the processing method, utilizing NH4HCO3 as a temporary pore former. Cr2AlC foams exhibited negligible oxidation up to 800 degrees C and excellent response up to 1300 degrees C due to the in-situ formation of an outer thin continuous protective layer of -Al2O3. The in-situ -Al2O3 protective layer covered seamlessly all the external surface of the pores, even when they present sharp angles and tight corners, reducing significantly the further oxidation of the foams. The compressive strength of the foams was 73 and 13MPa for 53vol% and 75vol% porosity, respectively, which increased up to 128 and 24MPa after their oxidation at 1200 degrees C for 1hour. The increase in the compressive strength after the oxidation was caused by the switch from inter- to transgranular fracture mode. According to the excellent high-temperature response, heat exchangers and catalyst supports are the potential application of these foams.