Abstract
Repetitive heating and cooling cycles inevitably cause crack damage of hot gas components of gas turbine engines, such as blades and vanes. In this study the self-healing capacity is investigated of mullite + ytterbium monosilicate (Yb2SiO5) as EBC material with Ti2AlC MAX phase particles embedded as a crack-healing agent. The effect of Ti2AlC in the EBC was compared with the self-healing ability of the mullite + Yb2SiO5 material. After introducing cracks by Vickers indentation on the surface of each sample, crack healing was realized by controlling the temperature and time during the post-heat-treatment process. For the mullite + Yb2SiO5 composite with Ti2AlC particles, crack healing occurred at 1000 °C, while in the case of the mullite + Yb2SiO5 composite without Ti2AlC, a sustained temperature of 1300 °C or higher was required. Compared with the healing of the mullite + Yb2SiO5 composite by the formation of a eutectic phase, the addition of Ti2AlC promoted healing via the oxidation of Ti and Al. Notably, the surface formation of a ternary oxide of Ti–Yb–O was confirmed, which completely covered the damage area. Consequently, the addition of a Ti2AlC MAX phase to the EBC composite resulted in a complete strength recovery, while the mullite + Yb2SiO5 composite without Ti2AlC showed a strength recovery of about 80%. Furthermore, by analyzing the indentation load–displacement curve to indicate the role of Ti2AlC, the addition of Ti2AlC improved both the hardness and stiffness of the composite.
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