Extended metastable Al solubility in cubic VAlN by metal-ion bombardment during pulsed magnetron sputtering: film stress vs subplantation

• Dynamic ion-recoil mixing of near-film-surface atomic layers is commonly used to increase the metastable solubility limit x(max) in otherwise immiscible thin film systems during physical vapor deposition. Recently, Al subplantation achieved by irradiating the film growth surface with Al+ metal-ion flux was shown to result in an unprecedented x(max) for VAlN, far above values obtained with gas ion irradiation. However, it is reasonable to assume that ion irradiation necessary for subplantation also leads to a compressive stress sigma buildup. In order to separate the effects of Al+ bombardment on sigma and x(max), and realize low-stress high-x(max) nitride alloys, we grow metastable cubic V1-xAlxN (0.17 amp;lt;= x amp;lt;= 0.74) films using reactive magnetron sputtering under different ion irradiation conditions. Al and V targets are operated in Ar/N-2 discharges employing (i) conventional DC (Ar+, N-2(+)), (ii) hybrid High-power pulsed magnetron sputtering (HIPIMS)/DC processing with one type of metal ion present (Al+ or V+/V2+), and (iii) HIPIMS with concurrent Al+ and V+/V2+ fluxes. Comparison to the ab initio calculated Al solubility limit reveals that x(max) = 0.55 achieved with V+/V2+ irradiation is entirely accountable for by stress. In contrast, Al+ fluxes provide a substantial increase in x(max) to 0.63, which is 12% higher than that expected based on the stress-induced increase in metastable solubility. Correlative stress and atom probe tomography data confirm that the metastable Al solubility enhancement is enabled by Al+ subplantation. The here proposed processing strategy allows for growth of single-phase cubic nitride alloys with significantly increased Al concentrations embodying tremendous promise for substantial improvements in high temperature oxidation resistance and mitigates the risk of stress-induced adhesive or cohesive coating failure. Published by AIP Publishing.

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TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Annan materialteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Other Materials Engineering (hsv//eng)

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