Growth of corrosion products on thermally sprayed coatings with FeAl intermetallic phases in aggressive environments

摘要

The cyclic corrosion behavior of coatings with FeAl intermetallic matrix was investigated in agressive gases for exposure times of up to 500 h. The composite coatings strengthened by a fine dispersive A1_2O_3 were thermally sprayed by HVOF method in Jet Kote 2 system. One portion of intermetallic coatings was sealed with an inorganic phosphate seal. The surfaces of HVOF sprayed coatings after a corrosion test were subjected to observation. A kinetics test was earned out by periodic method. Mass changes of the studied coatings during the corrosion test are presented. The surfaces of the composite coatings after the corrosion test in aggressive environments were analyzed by scanning microscopy observation. The results show that an adherent alumina scale and iron oxide layers were formed on all studied coatings. A stable alpha-Al_2O_3 phase on the surface of the studied coatings ensure high oxidation resistance. The corrosion rate is controlled by diffusion of corrosion products in the channels of oxide layer. An analysis of the corrosion products' phase composition was conducted by an X-ray diffraction method. The growth of corrosion products on the thermally sprayed coatings during the corrosion test and the chemical reactions between the corrosion products and aggressive environments are presented. All the results confirm good heat proofness of HVOF sprayed coatings with an intermetallic FeAl matrix.