Development and Oxidation of a Re_xO_(y~-) Modified Chromizing Coating

摘要

Novel reactive element oxide Re_xO_y (Re=Ce,Y)-modifed chromizing coatings have been developed by the first step of co-electrodeposition of Ni with CeO_2 or Y_2O_3 particles on a mild carbon steel and the subsequent step of diffusional chromizing on electrodeposited Ni-CeO_2/or Y_2O_3 composite films using a halide-activated pack-cementation method at 1120℃ for 4 h. By comparison, the coating processing was also performed on the carbon steel and on an electrodeposited Ni film without Re_xO_y addition. The thickness of the chromizing coating obtained was approximately 75 μm on the carbon steel and in a range of 55～60 μm on the other electrodeposited films with and without Re_xO_y. The former chromizing coating was mainly composed of α(Cr,Fe) phase and the latter coatings mainly composed of α(Cr, Ni) phase. All chromizing coatings were double-layered. However, the outer layer of coatings on the composite films was thicker and finer grained, in which the distribution of the Re_xO_y particles was observed. The oxidation at 940℃ showed that the Re_xO_y-modifed chromizing coatings were profoundly oxidation resistant as compared to the other two Re_xO_y-free coatings. It is proposed that the better performance of the Re_xO_y-modifed chromizing coating was associated with dispersion of the Re_xO_y particles, which exerted reactive element effect on the growth of chromia scale.