Impact of Si content on the thermal stability and oxidation resistance of cubic structured CrAlSiN coatings

Abstract

Thermal stability and oxidation resistance are crucial factors for evaluating the industrial potential of CrAlSiN coatings. Nevertheless, most of the studies focus on the microstructure and performance of CrAlSiN coatings with nanocomposite structure, the thermal stability, oxidation resistance, and the underlying mechanisms of CrAlSiN solid solution coatings still remain unknown. Here, Cr_1-x-zAl_xSi_zN coatings with gradient Si contents (z = 0–0.09) were prepared by arc evaporation. The influence of Si content on microstructure, mechanical properties, thermal stability, and oxidation resistance of CrAlSiN solid solution coatings is thoroughly discussed. The Cr_1-x-zAl_xSi_zN coatings are cubic structured up to z = 0.08, whereas the Cr_0.37Al_0.54Si_0.09N coating demonstrates a mixed cubic and hexagonal wurtzite structure. The hardness of cubic Cr_1-x-zAl_xSi_zN coatings increases with Si content rises due to solid solution effect and grain refinement, from the 27.7 ± 0.9 GPa of Cr_0.46Al_0.54N to the 36.1 ± 0.5 GPa of Cr_0.38Al_0.54Si_0.08N. While Cr_0.37Al_0.54Si_0.09N coating shows a declined hardness of 33.5 ± 0.6 GPa resulted from wurtzite formation. Furthermore, the breakage of CrN bonds is suppressed by Si-addition, where the formation temperature of hexagonal Cr₂N is enhanced from 1000 °C for Cr_0.46Al_0.54N to 1100 °C for all Si-containing coatings. Notably, oxidation resistance is also improved by increasing Si content owing to the promoted formation of dense Cr-rich oxide scale, grain refinement, and inhibited thermal decomposition process. After oxidation at 1100 °C for 15 h, Cr_0.44Al_0.55Si_0.01N, Cr_0.43Al_0.55Si_0.02N, Cr_0.42Al_0.54Si_0.04N, Cr_0.38Al_0.54Si_0.08N and Cr_0.37Al_0.54Si_0.09N coatings form oxides with thicknesses of ∼1.20, ∼0.95, ∼0.90, ∼0.90 and ∼ 0.64 μm, compared to the ∼1.49 μm of that on Cr_0.46Al_0.54N coating.