Experimental and computational study on the effect of yttrium on the phase stability of sputtered Cr–Al–Y–N hard coatings

The effect of Y incorporation into cubic Cr–Al–N (B1) was studied using ab initio calculations, X-ray diffraction and energy-dispersive X-ray analysis of sputtered quaternary nitride films. The data obtained indicate that the Y incorporation shifts the critical Al content, where the hexagonal (B4) structure is stable, to lower values. The calculated critical Al contents of x ≈ 0.75 for Cr1−xAlxN and x ≈ 0.625 for Cr1−x−yAlxYyN with y = 0.125 are consistent with experimentally obtained values of x = 0.69 for Cr1−xAlxN and x = 0.68 and 0.61 for Cr1−x−yAlxYyN with y = 0.02 and 0.06, respectively. This may be understood based on the electronic structure. Both Cr and Al can randomly be substituted by Y. The substitution of Cr by Y increases the phase stability due to depletion of non-bonding (anti-bonding) states, while the substitution of Al by Y decreases the phase stability mainly due to lattice strain.