High temperature wear behavior of micro and nanostructured Cr2O3 plasma sprayed coatings

Cr2O3 feedstock of nano and micron size particles were coated on low carbon steel by APS process. Ni-Al bond coat was used to improve the adhesion of coatings to substrate. Microstructural investigations were conducted by FESEM and X-ray diffractometery (XRD) was utilized for structural analysis. Wear behavior of the coatings was studied by ball on disk testing using alumina balls at room temperature and 300 and 500˚C under a load of 30N. Experimental results showed that both coatings consist of a layered structured of melted and semi-melted splats. However the nanostructured coating contained more semi-melted splats resulting more porosity compared to the microstructured coating. Tribological evaluation of the coatings revealed that the nanostructured coating exhibits lower friction coefficient in comparison to the microstructured Cr2O3 coating. Wear rate of the coatings decreased by increasing the temperature so that at 300 and 500˚C. The nanostructured coating presented better wear resistance. Improvement of wear resistance and decreasing the friction coefficient in nanostructured coating at different temperatures can be attributed to the effect of nanoparticles, higher hardness and also formation of compacted and adhesive tribofilm on the surface of the coating.