Influence of annealing temperature on microstructural, mechanical and chemical properties of CrAlN coatings

Abstract

CrAlN coatings were deposited using RF magnetron sputtering on to SS 304 substrates. To check the thermal stability of the coatings, they were annealed in air from 500 degrees C to 900 degrees C. Different characterizations such as structural, microstructural, mechanical and chemical studies were carried out. It was observed that the coatings retained their properties till 700 degrees C and then at 800 degrees C, the coatings showed degradation in some of the properties. Field Emission Scanning Electron Microscopy (FESEM) suggested no change in the microstructure till 800 degrees C and then, there was formation of cracks at the annealing temperature of 900 degrees C. From Raman analysis, the formation of some detectable oxides was confirmed for coatings annealed at 800 degrees C and 900 degrees C. At 800 degrees C, the coating showed a little decrease in the mechanical parameters which further degraded to a hardness value of 13.50 +/- 2.31 GPa as the annealing temperature increased to 900 degrees C. After carrying out these measurements, the chemical stability was also studied by doing corrosion test and Electrochemical Impedance Spectroscopy (EIS) of the coatings in 3.5% NaCl solution and the coatings were found to show outstanding corrosion resistance even after being annealed at a temperature as high as 800 degrees C which slightly decreased as the temperature increased further. Post corrosion mechanical properties of the annealed coatings were also observed.