Yttrium incorporation in Cr ₂ AlC: On the metastable phase formation and decomposition of (Cr,Y) ₂ AlC MAX phase thin films

Abstract Herein we report on the synthesis of a metastable (Cr,Y) 2 AlC MAX phase solid solution by co‐sputtering from a composite Cr–Al–C and elemental Y target, at room temperature, followed by annealing. However, direct high‐temperature synthesis resulted in multiphase films, as evidenced by X‐ray diffraction analyses, room‐temperature depositions, followed by annealing to 760°C led to the formation of phase pure (Cr,Y) 2 AlC by diffusion. Higher annealing temperatures caused a decomposition of the metastable phase into Cr 2 AlC, Y 5 Al 3 , and Cr‐carbides. In contrast to pure Cr 2 AlC, the Y‐containing phase crystallizes directly in the MAX phase structure instead of first forming a disordered solid solution. Furthermore, the crystallization temperature was shown to be Y‐content dependent and was increased by ∼200°C for 5 at.% Y compared to Cr 2 AlC. Calculations predicting the metastable phase formation of (Cr,Y) 2 AlC and its decomposition are in excellent agreement with the experimental findings.