Thermal stability of multi-layered AlCrN/Cr/AlCrN coatings at elevated temperatures for low thermal emissivity applications

Abstract Multi-layered AlCrN/Cr/AlCrN coatings were designed and deposited on Ni-based substrates by a cathodic arc ion plating system for low thermal emissivity applications. The multi-layered coatings annealed at different temperatures in air and vacuum were systematically investigated by GIXRD, EPMA, XPS, DSC, GDOES, FESEM, HR-TEM and scratch tester as well as the infrared properties evaluation. The as-deposited AlCrN layer was consisted of Cr2N nanocrystallites embedded in AlCrN amorphous matrix, inhibiting element diffusion and presenting higher infrared emissivity. The amorphous matrix began to crystallize as fcc-Cr(Al)N structure at 750 °C. The diffusion of Ni element from the substrate to the middle Cr layer was observed as well as the Cr-rich oxides were substituted by chrome‑aluminum oxides above 750 °C in air. The grain boundaries resulted from the crystallization of amorphous AlCrN layer could promote the penetration of O element from air and the diffusion of Ni element from the substrate. The AlCrN/Cr/AlCrN coatings vacuum-annealed above 750 °C performed lower infrared emissivity than the as-deposited one, while the coatings air-annealed above 750 °C showed higher infrared emissivity than vacuum-annealed ones due to the low extinction coefficient of oxides formed on the coating surface. The multi-layered AlCrN/Cr/AlCrN coating could be proposed for low infrared emissivity applications below 750 °C.