Hot corrosion behavior of NbSi2/SiO2-Nb2O5 multilayer coating on Nb alloy

A NbSi2/SiO2-Nb2O5 multilayer coating, consisting of a NbSi2 inner layer and a SiO2-Nb2O5 outer layer, was prepared on Nb alloy through halide activated pack cementation (HAPC) and microarc oxidation (MAO). The hot corrosion behaviors of the single NbSi2 coated and the NbSi2/SiO2-Nb2O5 coated Nb alloys were comparatively investigated with a mixture of Na2SO4/NaCl (3:1 wt.%) salt at 900 degrees C. The growth kinetics of the corroded scales follow the parabolic laws, and the parabolic rate constants of the NbSi2 coated and the NbSi2/SiO2-Nb2O5 coated specimens were 2.16 x 10(-3) mms(-2) and 1.04 x 10(-3) mms(-2), respectively. During the corroding process, the SiO2-Nb2O5 outer layer that serves as a barrier promotes the formation of continuous SiO2 scale, and isolates the NbSi2 layer from the corrosion salt. The lower corrosion rate of the NbSi2/SiO2-Nb2O5 coated specimens is attributed to the formation of the protective SiO2 corroded scale. (C) 2018 Elsevier B.V. All rights reserved.