Structural and Phase State and Properties of Gradient and Bilayer Al2O3/Cr2O3 Coatings Obtained by Detonation Spraying

This study aims to compare the structural, mechanical, tribological, and corrosion properties of gradient and bilayer Al2O3/Cr2O3 coatings obtained by detonation spraying on 316L stainless steel. The coatings were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, instrumental indentation, scratch testing, ball-on-disk tribological testing, and potentiodynamic polarization in a 3.5% NaCl solution. The results showed that the gradient Al2O3/Cr2O3 coating had a denser and more homogeneous structure than the bilayer coating. Quantitative SEM image analysis showed that the apparent porosity decreased from 1.285% for the bilayer coating to 0.934% for the gradient coating. Instrumental indentation revealed an increase in hardness from approximately 401 HV to 462 HV and an increase in elastic modulus from about 173 GPa to 183 GPa. The gradient coating also demonstrated higher critical loads during scratch testing, indicating improved resistance to crack initiation and coating failure. Tribological tests showed a lower and more stable coefficient of friction for the gradient coating, decreasing from approximately 0.58–0.60 to 0.52–0.55. Potentiodynamic polarization measurements showed that the corrosion current density decreased from 0.50540 to 0.24155 µA/cm2, while the corrosion rate decreased from 0.00894 to 0.00428 mm/year. These results demonstrate that the gradient coating architecture improves the performance of Al2O3/Cr2O3 coatings by reducing porosity, increasing structural integrity, and promoting an improved structural integrity and reduced defect-related stress concentration through the coating thickness. Therefore, gradient Al2O3/Cr2O3 coatings obtained by detonation spraying are promising for applications requiring enhanced wear and corrosion resistance.