Improvement in fracture toughness and wear resistance of plasma-sprayed chromia coating by addition of YSZ nanoparticles

In the present research, wear behavior of Cr2O3-20YSZ (CZ) and Cr2O3 (C) coatings created using atmospheric plasma spray (APS) process was evaluated. For this purpose, Cr2O3 and YSZ nanopowders were produced after milling for 5h in a high-energy ball mill and subsequently plasma spraying of the agglomerated powders was carried out on 304L substrates. Microstructural characterization of these ceramic coatings was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and optical microscope. Mechanical tests including adhesive strength, fracture toughness, and micro-hardness were used so as to explain the coatings wear behavior. Sliding wear test was conducted using a ball-on-disk configuration against an alumina counterpart at room temperature. Addition of YSZ particles to the Cr2O3 matrix due to the phase transformation toughening mechanism associated with tetragonal zirconia resulted in an increase in the fracture toughness while decreased the micro-hardness. It was found that the composite coatings had the friction coefficients of the proper order of 0.11-0.15. The CZ composite coating compared to the C coating showed the higher wear resistance so that the weight loss was obtained as 11 and 31 mg, respectively. Observation of the wear tracks of the coatings indicated that the lower wear rate of the CZ coating was attributed to its higher toughness and therefore filling the pores due to the higher plastic deformation of its wear debris.