Effect of target peak power density on the phase formation, microstructure evolution, and mechanical properties of Cr2AlC MAX-phase coatings

The applicability of Cr2AlC MAX-phases as protective coatings in energy conversion or aerospace applications requires a dense, single-phase structure. Therefore, we study the effect of target power density and substrate bias on phase formation, microstructure evolution, and mechanical properties of Cr2AlC coatings utilizing direct current (DCMS) and high-power pulsed magnetron sputtering (HPPMS). Generally, HPPMS results in coatings with superior density and hence larger elastic moduli compared to DCMS, indicating that ion bombardment by ionized film-forming species is beneficial. However, decreasing the substrate bias to -200 V for DCMS and -100 V for HPPMS favors the ion bombardment induced formation of the disordered (Cr,Al)(2)C-x solid solution. It is evident that there is an optimum moderate ion energy for the formation of dense Cr2AlC coatings. Too low energy results in the formation of under-dense coatings. Too high energy yields the formation of (Cr,Al)(2)C-x in addition to Cr2AlC.