Fabrication and mechanical properties of high purity of Cr2AlC coatings by adjustable Al contents

The effect of Al content on phase structure and mechanical properties of vacuum annealed Cr-Al-C coatings was investigated. Cr-Al-C coatings were deposited by co-sputtering of Cr2Al and Al targets in optimized CH4/Ar atmosphere. The atomic content of Al was adjusted through the control of Al target current from 0.5 A to 3.0 A, thus Cr-Al-C coatings with different stoichiometric ratios were obtained. After 1.5 h thermal annealing at 750 °C in vacuum, Cr2AlC MAX phase was observed from the XRD measurements. The Rietveld refinement of XRD spectra results indicated that the annealed coatings were composed of Cr2AlC, Al8Cr5 and Cr7C3 phases with different amounts. With the increase of Al content, the hardness and modulus of the Cr2AlC MAX phase coatings varied from 10.17 to 19.00 GPa and 198.43 to 267.62 GPa, respectively, while the toughness suffered an obvious decline. HRTEM analysis demonstrated that the excess of Al content resulted in the formation of Al8Cr5 and Al segregation at grain boundaries, which led to the deterioration of mechanical properties.