Al2O3–FeCrAl composites and functionally graded materials fabricated by reactive hot pressing

Al2O3–FeCrAl composites were fabricated by mixing Fe2O3, Al and Cr powders and then reactive hot pressing. The high temperature alloy FeCrAl was formed by the reaction of extra Al, Cr and the Fe reduced from Fe2O3. The Al2O3–FeCrAl composites with various Al2O3 fractions were successfully fabricated by the proper addition of extra Fe, Cr, Al or Al2O3 powders. A five-layer functionally graded material of YSZ–FeCrAl was fabricated using the Al2O3–FeCrAl composites with compositions of 25, 53.2 and 75 vol.% Al2O3 as interlayer. The results from XRD analysis, optical microscope observation and thermal cycling test show that the composites fabricated by this method consist of α-Al2O3 phase and (Fe, Cr, Al) solid solution. The α-Al2O3 grain formed by this in-situ reaction between Fe2O3 and Fe is ultrafine and uniform distribution. The three-point bending strength is 305.0 MPa for the composite with 53.2 vol.% Al2O3 prepared by the reactive hot pressing, about 20% higher than that of the composite with same composition prepared by ex situ hot pressing method (252.0 MPa). No cracking was found in the functionally graded materials after 10 thermal cycles up to 1000 °C due to the better metal–ceramic bond, continuous in microstructure at interface of FGM and good oxidation resistance component FeCrAl alloy formed in the FGM.