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

Abstract

The isothermal oxidation behaviour of Cr 2 AlC-MAX phase (ternary alloy with general formula M n+1 AX 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) 2 C x to the ordered Cr 2 AlC-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 Cr 2 AlC 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.