A comparative study of reactive direct current magnetron sputtered CrAlN and CrN coatings

Approximately 1.5 mu m thick CrN and CrAIN coatings were deposited on silicon and mild steel substrates by reactive direct current (DC) magnetron sputtering. The structural and mechanical properties of the coatings were characterized using X-ray diffraction (XRD) and nanoindentation techniques, respectively. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy (XPS). The surface morphology of the coatings was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD data showed that the CrN and CrAIN coatings exhibited B1 NaCl structure. Nanoindentation measurements showed that as-deposited CrN and CrAIN coatings exhibited a hardness of 18 and 33 GPa, respectively. Results of the surface analysis of the as-deposited coatings using SEM and AFM showed a more compact and dense microstructure for CrAIN coatings. The thermal stability of the coatings was studied by heating the coatings in air from 400 to 900 degrees C. The structural changes as a result of heating were studied using micro-Raman spectroscopy. The Raman data revealed that CrN coatings got oxidized at 600 degrees C, whereas in the case of CrAIN coatings, no detectable oxides were formed even at 800 degrees C. After annealing up to 700 degrees C, the CrN coatings displayed a hardness of only about 7.5 GPa as compared to CrAIN coatings, which exhibited hardness as high as 22.5 GPa. The potentiodynamic polarization measurements in 3.5% NaCl solution indicated that the CrAIN coatings exhibited superior corrosion resistance as compared to CrN coatings. (c) 2006 Elsevier B.V. All rights reserved.