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This work reports the oxidation and crack healing behavior of a fine-grained (~2 μm) Cr2 AlC MAX phase ceramic. The oxidation behavior was investigated in the temperature range 900°C-1200°C for times up to 100 h. The material showed a good oxidation resistance, owing to the formation of a dense and thin α- Al2 O3 layer. The microstructure, composition and thickness of the oxide scale were characterized. Its oxidative crack healing behavior as a function of temperature, healing time, and initial crack size was studied systematically. The material showed excellent healing behavior. The main crack healing mechanism is the filling of the crack by oxides well adhering to the crack faces. The crack geometry before and after healing was characterized by X-ray tomography. Three-point bend tests showed the dependence of strength recovery at 1100°C as a function of initial crack length and healing time. [ABSTRACT FROM AUTHOR]

Using spark plasma sintering, Ti3 AlC2/ W composites were prepared at 1300°C. They contained 'core-shell' microstructures in which a Ti xW1− x 'shell' surrounded a W 'core', in a Ti3 AlC2 matrix. The composite hardness increased with W addition, and the hardening effect is likely achieved by the Ti x W1− x interfacial layer providing strong bonding between Ti3 AlC2 and W, and by the presence of hard W. Microstructural development during high-temperature oxidation of Ti3 AlC2/ W composites involves α- Al2 O3 and rutile ( TiO2) formation ≥1000°C and Al2 TiO5 formation at ~1400°C while tungsten oxides appear to have volatilized above 800°C. Likely due to exaggerated, secondary grain growth of TiO2-doped alumina and the effect of W addition, fine (<1 μm) Al2 O3 grains formed dense, anisomorphic laths on Ti3 AlC2/5 wt% W surfaces ≥1200°C and coarsened to large (>5 μm), dense, TiO2-doped Al2 O3 clusters on Ti3 AlC2/10 wt% W surfaces ≥1400°C. W potentially affects the oxidation behavior of Ti3 AlC2/ W composites beneficially by causing formation of Ti x W1− x thus altering the defect structure of Ti3 AlC2, resulting in Al having a higher activity and by changing the scale morphology by forming dense Al2 O3 laths in a thinner oxide coating, and detrimentally through release of volatile tungsten oxides generating cavities in the oxide scale. For Ti3 AlC2/5 wt% W oxidation, the former beneficial effects appear to dominate over the latter detrimental effect. [ABSTRACT FROM AUTHOR]