Microstructure and high-temperature corrosion behavior of a Cr-Al-C composite

A Cr-Al-C composite was successfully synthesized by a hot-pressing method using Cr, Al, and graphite as starting materials. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses revealed that the composite contained Cr2AlC, AlCr2, Al8Cr5, and Cr7C3. The orientation relationships and atomic-scale interfacial microstructures among Cr2AlC, AlCr2, and Al8Cr5 are presented. This composite displays both excellent high-temperature oxidation resistance in air and hot-corrosion resistance against molten Na2SO4 salt. The parabolic rate constants for the oxidation in air at 1000 degrees, 1100 degrees, and 1200 degrees C are 3.0 x 10(-12), 6.2 x 10(-11), and 6.2 x 10(-10) kg(2) (m(4).s)(-1), respectively, while the linear weight gain rates for the hot corrosion of Na2SO4-coated samples at 900 degrees and 1000 degrees C are, respectively, 1.2 x 10(-3) and 4.4 x 10(-3) mg (cm(2).h)(-1). The mechanism of the excellent high-temperature corrosion resistance can be attributed to the formation of a protectively alumina-rich scale.