Comparison of Mechanical Properties of Nanostructured Cr2O3 and Cr2O3-20YSZ Plasma-sprayed Coatings

In this research, nanostructured Cr2O3 (C) and Cr2O3-20YSZ (CZ) coatings were deposited using Atmospheric Plasma Spray (APS) process and subsequently their mechanical properties including fracture toughness, hardness and bonding strength were evaluated and compared with each other. For this purpose, Cr2O3 and YSZ nano-powders were firstly prepared by high-energy planetary ball milling and then mixed in the given volume. To use the powder mixture in the plasma spraying, the powders were agglomerated and sprayed onto a 304L steel substrate. Microstructural studies of the powders and coatings were carried out through Filed Emission Scanning Electron Microscope (FE-SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD) analysis. XRD patterns of the milled powders and the coatings indicated there was no newly-appeared phase during the milling and plasma spraying process. Porosity of the coatings was measured using an optical microscope by image analysis of their cross-sectional images. Mechanical properties evaluation showed that both coatings have high adhesive strength in the range of 43-49 Mpa. Although the addition of YSZ nanoparticles to the chromia coating slightly decreased the coating hardness, it caused a considerable increase in the coating toughness due to the zirconia transformation toughening mechanism.