Microstructure and High-temperature Oxidation Behavior of Ti3 AlC2/ W Composites.

Using spark plasma sintering, Ti₃ AlC₂/ W composites were prepared at 1300°C. They contained 'core-shell' microstructures in which a Ti _xW_{1− 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 W_{1− 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 W_{1− 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]