Effect of Cr on Corrosion Behavior of Laser Cladding Ni-Cr-Mo Alloy Coatings in Sulfuric Acid Dew Point Corrosion Environment

Abstract

Ni-Cr-Mo alloy coatings with different content of Cr element were produced on carbon structural steel by laser cladding. Coatings exhibited similar phase composition containing γ-Ni solid solution and similar microstructure composed of primary grains and eutectics with segregated Mo. Corrosion behavior of coatings in a sulfuric acid dew point corrosion environment were investigated through the combination of immersion test, electrochemical measurements, and surface analysis. Coatings exhibited similar passive behavior and passive film with a bilayer structure consisting of a compact inner layer and a porous outer layer. An increase in Cr resulted in a more protective passive film with thicker and more compacting inner layer. However, the corrosion resistance was firstly degraded as the content of Cr increased from 18 wt.% to 22 wt.%, and then improved as the content of Cr increased from 22 wt.% to 26 wt.%. This phenomenon was attributed to the competition effect between the increase in Cr and relative decrease in Ni.