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

Abstract

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 °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 × 10−3 mm s−2 and 1.04 × 10−3 mm s−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.