Microstructure and Thermal Shock Resistance of Cr_2O_3 Ceramic Coatings Deposited by Supersonic Atmosphere Plasma Spraying

Cr2O3 based(Cr2O3-Ni-5%Al) coatings as an alternative for mold materials were deposited onto a pure copper substrate via a supersonic atmosphere plasma spray(SAPS).The coatings were examined by X-ray diffraction,scanning electron microscopy,image software,color 3D laser scanning microscopy and micro-hardness tester,respectively.The thermal shock test was conducted at 450 ℃ and 600 ℃,respectively.There was a slight difference between the crystalline degrees of Cr2O3 without the phase transfor-mation at various temperatures.The as-sprayed coating displayed a bimodal surface microstructure,which composed of well melted regions and partially melted particles.Furthermore,a typical porous lamellar structure was observed in the fracture surface,and the chromium-rich regions were uniformly dispersed in the cross-section of the as-sprayed coating.The Cr2O3 coating possessed the sur-face roughness value(Ra) of 4.763 μm,porosity of 1.2% and micro-hardness of 1 628 MPa.The hemispherical dome of samples spalled with the greater surface area after 127.4 and 58.6 average thermal shock cycles but the main part of cylindrical samples was intact,so the coating exhibited the superior thermal shock resistance.The results show that this supersonic atmosphere plasma spray method is suitable for the preparation of the extreme temperature variations coating for casting mould.