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Due to their applicability for manufacturing dense, hard and stable coatings, Physical Vapor Deposition (PVD) techniques, such as High Power Impulse Magnetron Sputtering (HiPIMS), are currently used to deposit transition metal nitrides for tribological applications. Cr-Al-N is one of the most promising ceramic coating systems owing to its remarkable mechanical and tribological properties along with excellent corrosion resistance and high-temperature stability. This work explores the possibility of further improving Cr-Al-N coatings by modulation of its microstructure. Multilayer-like Cr1−xAlxN single films were manufactured using the angular oscillation of the substrate surface during HiPIMS. The sputtering process was accomplished using pulse frequencies ranging from 200 to 500 Hz and the resulting films were evaluated with respect to their hardness, Young’s modulus, residual stresses, deposition rate, crystallite size, crystallographic texture, coating morphology, chemical composition, and surface roughness. The multilayer-like structure, with periodicities ranging from 250 to 550 nm, were found associated with misorientation gradients and small-angle grain boundaries along the columnar grains, rather than mesoscopic chemical modulation of the microstructure. This minute modification of microstructure along with associated compressive residual stresses are concluded to explain the increased hardness ranging from 25 to 30 GPa, which is at least 20% over that expected for a film of the same chemical composition grown by a conventional PVD processing route.

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The use of carbonate molten salts for the new generation of concentrated solar power (CSP) plants have been considered and analysed during the last years to improve the efficiency of energy generation. However, the high temperature and corrosivity of the salts pose a risk on safety and profitability of the technology requiring more resistant materials. In this study, two alumina-forming austenitic (AFA) alloys corresponding to modified OC4 and HR224 grades, were exposed to the eutectic ternary Li2CO3-K2CO3-Na2CO3 (32.1-34.5-33.4 wt.%) salt mixture at 650 °C for 1000 h. The evolution of weight change along the exposure time and analysis of the resulting scales by means of scanning electron microscopy (SEM), X-Ray diffraction (XRD), and glow discharge optical emission spectroscopy (GDOES) revealed a good performance of both steel grades associated with the formation of multi-layered corrosion products. Whereas both alloys undergo external oxidation with the formation of NiO, internal oxidation with the formation of two spinels is the case of HR224. The rate of corrosion is significantly lower than those reported in molten carbonated in non-AFA alloys, allowing to recommend OC4 and HR224 for use in the carbonate-based CSP.

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