Part I. Mechanism of oxidation of Cr₂AlC films in temperature range 700–1200°C

Abstract

The isothermal oxidation behaviour of Cr₂AlC-MAX phase (ternary alloy with general formula M_n+1AX_n: M = early transition metal, A = A-group element, mostly IIIA or IVA, X = C or N, n = 1–3) films on alumina substrates was investigated at temperatures between 700 and 1200°C for hold times of 1 to 30 h. The influence of the annealing temperature and time on the structure, surface morphology and microstructure evolution was studied. It was found that two processes occur simultaneously in these layers. These are the transformation of the disordered solid solution (Cr,Al)₂C_x to the ordered Cr₂AlC-MAX phase and the oxidation of the MAX phase. In this work, a detailed discussion of these processes is given. Moreover, a schematic model of the associated structural and chemical changes in the annealed Cr₂AlC layers based on the X-ray diffraction (XRD), Energy Dispersive X-ray (EDX), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and magnetic results was developed.

Keywords:

• Thin films
• Phase transition
• Oxides

Acknowledgments

The financial support of the Deutsche Forschungsgemeinschaft under LE1373/10-2 is greatly acknowledged, as well as the help of M. to Baben and J. M. Schneider (RWTH Aachen) for the production of the film samples. 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.