Effect Of Cr Content On High Temperature Oxidation Behavior Of Low-Cr Alloy Sputtering Coating

Metallic materials applied as interconnect of solid oxide fuel cell are facing several problems such as oxidation and the evaporation of Cr at operation temperature, which blocks the commercialization of SOFC. Therefore, improving the oxidation resistance of alloy materials and suppressing the evaporation of Cr has becoming the focus of current investigations. Based on previous works, three kinds of low-Cr alloys with different contents of Cr (Si-free) were prepared. By magnetron sputtering, columnar nano-grain coatings were deposited on the cast alloys with the same compositions. The oxidation behavior and the surface scale electrical property of both cast alloys and their sputtered coatings were investigated. The results are showed as below.(1). The diameters of the columnar nano-grains of sputtered coatings were smaller than20nm.(2). After oxidation in air at700℃for200h, a double-layer oxide scale with a CoFe2O4spinel outer layer and a continuous Cr2O3inner layer was thermally converted on the sputtered coating with6%Cr, which reduced the oxidation rate of the coating. For the sputtered coating with5%Cr, some internal oxides rich in Cr were formed. However, they were discrete and uncompleted continuous. The oxidation resistance was a little better than that of its cast alloy. In case of the sputtered coating with4%Cr, the oxidation resistance was lower than that of its cast alloy.(3). After oxidation in air at800℃for200h, only on the sputtered coating with6%Cr can a double-layer structure be formed, which contributes to the increase of oxidation resistance. For the sputtered coatings with5%and4%Cr and cast alloys, the protective Cr inner layer cannot be developed and their oxidation mass gain exhibited a continued increase over time.(4). The area specific resistances (ASRs) of cast alloys with different contents of Cr as well as the corresponding sputtered coatings after oxidation at700℃and800℃in air for200h were measured by four-point method. Although double-layer oxide scales were developed on sputtered coatings and the oxidation resistance was improved, the electrical conductivity of Cr2O3is lower than those of other oxides, leading to a higher scale ASR compared to cast alloys.