Demonstrating the self-healing behaviour of some selected ceramics under combustion chamber conditions

Abstract

<p>Closure of surface cracks by self-healing of conventional and MAX phase ceramics under realistic turbulent combustion chamber conditions is presented. Three ceramics namely; Al<sub>2</sub>O<sub>3</sub>, Ti<sub>2</sub>AlC and Cr<sub>2</sub>AlC are investigated. Healing was achieved in Al<sub>2</sub>O<sub>3</sub> by even dispersion of TiC particles throughout the matrix as the MAX phases, Ti<sub>2</sub>AlC and Cr<sub>2</sub>AlC exhibit intrinsic self-healing. Fully dense samples (>95%) were sintered by spark plasma sintering and damage was introduced by indentation, quenching and low perpendicular velocity impact methods. The samples were exposed to the oxidizing atmosphere in the post flame zone of a turbulent flame in a combustion chamber to heal at temperatures of approx. 1000 °C at low pO<sub>2</sub> levels for 4 h. Full crack-gap closure was observed for cracks up to 20 mm in length and more than 10 μm in width. The reaction products (healing agents) were analysed by scanning electron microscope, x-ray microanalysis and XRD. A semi-quantification of the healing showed that cracks in Al<sub>2</sub>O<sub>3</sub>/TiC composite (width 1 μm and length 100 μm) were fully filled with TiO<sub>2</sub>. In Ti<sub>2</sub>AlC large cracks were fully filled with a mixture of TiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub>. And in the Cr<sub>2</sub>AlC, cracks of up to 1.0 μm in width and more than 100 μm in length were also completely filled with Al<sub>2</sub>O<sub>3</sub>.</p>