Effect of N2 flow rate on structural and infrared properties of multi-layer AlCrN/Cr/AlCrN coatings deposited by cathodic arc ion plating for low emissivity applications

The effect of N-2 flow rate on structural, composition, deposition rate, electrical and infrared properties of the multi-layer AlCrN/Cr/AlCrN tandem coatings have been studied. The coatings were designed and prepared by a cathodic arc ion plating system at various N-2 flow rates for low emissivity applications. The results showed that the thickness of AlCrN layers decreased continuously with increasing N-2 flow rate. Structure and elemental composition of the deposited coatings strongly depended on N-2 flow rate. X-ray diffraction analysis showed that for 10-80 sccm, the coatings exhibited a single (fcc) phase, for 120-160 sccm, an amorphous phase was obtained. The phase formation has been confirmed by transmission electron microscopy diffraction patterns. As for electrical resistivity, the AlCrN layers turned from conductive, semiconductive, to dielectric behavior. In practice for low emissivity applications, the deposited multi-layer coatings exhibited emissivity values among 0.0748-0.1193, which rose with increased N-2 flow rate. Among all the phases, the coating with an amorphous AlCrN layer (160 sccm) presented an outstanding thermal stability and had an emissivity of 0.1194 even after annealing at 800 degrees C for 10 h in air. It was observed that the amorphous AlCrN layer effectively controlled the inward diffusion of O and the outward diffusion of Cr, Al and Ni from substrate, which rendered this multi-layer coating a potential material for low emissivity applications at high temperature.