Microstructure, phase composition and mechanical properties of plasma sprayed Al2O3, Cr2O3 and Cr2O3-Al2O3 composite coatings

Abstract

In the present work, chromia and alumina coatings were produced by atmospheric plasma spray process. Phase composition, microstructure and mechanical properties of chromia and alumina composite coatings on carbon steel substrates were studied and compared to individual Cr2O3 and Al2O3 coatings. Morphology and microstructure of coatings were characterized using scanning electron microscopy equipped by EDS. The porosity of the plasma-sprayed coatings was measured by the Archimedes water immersion technique and image analysis method. X-ray diffraction was employed to identify phase composition of coatings. Also some mechanical properties such as bonding strength, Vickers microhardness and resistance to crack propagation of coatings were measured. The results showed different phases for Al2O3 in different coatings while Cr2O3 remained in eskolaite phase in all of the coatings. Addition of 75wt% Cr2O3 prevented formation of metastable and undesirable γ-Al2O3 phase. Alumina and rich-alumina coatings showed denser microstructure and higher flattening degree of splats as well as lower surface roughness. Bonding strength of individual Cr2O3 and Al2O3 coatings was higher than composite one. Vickers microhardness increased with addition of Cr2O3. Alumina improved spray ability and crack propagation resistant of chromia.