Part II. Oxidation of yttrium doped Cr₂AlC films in temperature range between 700 and 1200°C

Abstract

The isothermal oxidation behaviour of Cr₂AlC films deposited with 0·1–0·3 at.%Y addition on alumina substrates was investigated at temperatures between 700 and 1200°C for hold times of 1 to 30 h. It was found that the Y atoms impede the bulk diffusion of Al and Cr atoms and, thus, the initial transformation of the disordered solid solution (Cr, Al)₂C_x to the ordered Cr₂AlC-MAX phase. It also reduces the oxidation rate of the ordered Cr₂AlC-MAX phase and promotes the α-Al₂O₃ phase formation relative to the other alumina on the surface and leads to better adhesion of the layers. 0·3 at.%Y was found to promote the formation of α-Al₂O₃ relative to the other possible phases most strongly for 700–900°C. However, 0·2 at.%Y addition was found to cause the best oxidation resistance at 1200°C. The model introduced in part I was developed further.

Keywords:

• Thin films
• Phase transition
• Oxides