Microstructural and compositional design of Cr2AlC MAX phases and their impact on oxidation resistance

Abstract

The oxidation of MAX phases has largely been investigated, but the effect of secondary phases and microstructure is still unclear. We report on the effect of reactive and non-reactive sintering, and starting powders, on the microstructure, phase formation, and chemical composition of Cr2AlC MAX phases. The grain sizes are shown to be sensitive to both the processing method and the starting powders. Secondary phases were observed mostly in reactively sintered samples as Cr7C3 and AlCr2 were identified, and Al contents varied between 24.4 and 28.0 at%. Finally, the oxidation behavior of the produced MAX phases was evaluated after 60 and 120 min at 1100 °C. The Al content, the average grain size of the as-sintered samples, and the presence of secondary phases affected the decomposition of the MAX phase into Cr-carbides in the vicinity of the oxide scale and the composition of the oxide scale, respectively.