Phase Stability of Nanolaminated Epitaxial (Cr_1–xFe_x)₂AlC MAX Phase Thin Films on MgO(111) and Al₂O₃(0001) for Use as Conductive Coatings

In this study, we model the chemical stability in the (Cr1–xFex)2AlC MAX phase system using density functional theory, predicting its phase stability for 0 < x < 0.2. Following the calculations, we have successfully synthesized nanolaminated (Cr1–xFex)2AlC MAX phase thin films with target Fe contents of x = 0.1 and x = 0.2 by pulsed laser deposition using elemental targets on MgO(111) and Al2O3(0001) substrates at 600 °C. Structural investigations by X-ray diffraction and transmission electron microscopy reveal MAX phase epitaxial films on both substrates with a coexisting (Fe,Cr)5Al8 intermetallic secondary phase. Experiments suggest an actual maximum Fe solubility of 3.4 at %, corresponding to (Cr0.932Fe0.068)2AlC, which is the highest Fe doping level achieved so far in volume materials and thin films. Residual Fe is continuously distributed in the (Fe,Cr)5Al8 intermetallic secondary phase. The incorporation of Fe results in the slight reduction of the c lattice parameter, while the a lattice parameter remains unchanged. The nanolaminated (Cr0.932Fe0.068)2AlC thin films show a metallic behavior and can serve as promising candidates for highly conductive coatings.