Effect of Addition of Multimodal YSZ and SiC Powders on the Mechanical Properties of Nanostructured Cr2O3 Plasma-Sprayed Coatings

In this research, the effect of the addition of multimodal yttria-stabilized zirconia (YSZ) and SiC reinforcements on the mechanical properties of Cr2O3 plasma-sprayed coatings was studied. For this purpose, the starting powders were ball milled for 5h and then mixed and agglomerated, prior to spraying. Cr2O3, Cr2O3-20YSZ (CZ), and Cr2O3-20YSZ-10SiC (CZS) coatings were then deposited onto 304L steel substrates using the atmospheric plasma spray process. Microstructural evaluations of the initial/milled powders and the plasma-sprayed coatings were conducted through x-ray diffraction, field emission scanning electron microscopy (FESEM) equipped with energy-dispersive x-ray spectroscopy and porosity measurements. The microscopic images indicated that the multimodal milled powders resulted in nanostructured coatings. Mechanical tests including adhesive strength, fracture toughness, and micro-hardness were used to understand the dependence of the properties of coatings and their microstructure. Adding tough YSZ particles to the C coating considerably increased the toughness through the phase transformation-toughening mechanism of tetragonal zirconia while decreasing micro-hardness of the coating; therefore, intrinsically hard SiC particles were added to the CZ coating to deal with the reduced hardness. Moreover, when compared to pure C coating, CZ, and CZS Composite coatings showed comparable bonding strengths and higher porosities.