Crack healing in Y-doped Cr₂AlC-MAX phase coatings

Abstract

Self-healing materials facilitate a design concept which includes damage management, where damage that is inflicted during operation can be healed autonomously. It has been shown that the M_n+1AX_n phases Ti₃AlC₂, Ti₂AlC and Cr₂AlC exhibit such behaviour. Cracks are filled and hence healed by oxidation products of the M and A elements in the MAX phase at the high operating temperatures in which they are used. After crack healing the fracture strength is recovered to the level of the virgin material. In this work, the Cr₂AlC-MAX phase was shown to exhibit excellent self-healing properties. Cracks of maximum widths of approximately 500 nm and 4 μm could be healed after a 3–5 h anneal at 900 and 1200°C, respectively. In this system, the addition of Y on the rate of oxidation and on the self-healing behaviour was investigated.

Keywords:

• Thin films
• Self-healing
• Oxides

Acknowledgements

The support of M. To Baben and J.M. Schneider (RWTH Aachen) for the preparation of the thin film samples is greatly acknowledged. The help of C. Kwakernaak, W.G. Sloof and F.D. Tichelaar (Surface and Interfacing Science (TU Delft) and National Centre for HREM, TU Delft) with regard to the TEM measurements is also greatly acknowledged. The authors are also grateful to C. Leyens for helpful discussions as well as for the help of S. Heinze during the experiments.