Structural, mechanical and corrosion behaviors of the homogeneous and gradient CrAlSiN coatings in 3.5% NaCl solution

The homogeneous and gradient CrAlSiN coatings were prepared at constant and graded sputtering power respectively, and their structural, mechanical and corrosion behaviors were compared. Results showed that both coatings were composed of fcc-(Cr, Al)N, hcp-Cr2N, hcp-AlN and amorphous Si3N4, and exhibited a distinct columnar structure. However, the homogenous CrAlSiN coating possessed a uniform chemical composition and phase structure, while the gradient one exhibited compositional and microstructural variations from the coating/substrate interface to surface. Compared with the homogenous one, the gradient CrAlSiN coating possessed nearly equivalent hardness, but better performance in plastic deformation resistance and adhesive strength. Corrosion tests show that pitting corrosion occurred around micro-particles for both CrAlSiN coatings. However, the gradient CrAlSiN coating exhibited the lower corrosion rate of 3.63 × 10−4 mm/a and higher protective efficiency of 97.4%, which was related to the improved surface quality and refined columnar structure, and to the alternating layers of different compositions from the coating/substrate interface to surface promoting redistribution of current flow in coating.