Investigation on the corrosion behavior of Ni-Cr-Mo-W-xSi laser cladding coating in H2S corrosion environment

Abstract

Ni-Cr-Mo-W-xSi laser cladding coating with Si mass fraction changing from 0, 1 wt .%, 3 wt .% to 5 wt .% were fabricated by laser cladding technology. The influence of Si content on the phase constitution, microstructure evolution and high temperature sulfur corrosion resistance were investigated. Experimental results showed that the order of corrosion resistance under H2S corrosion environment at 500-600℃ was S1 > S0 > S3 > S5. The optimized content of Si addition for Ni-Cr-Mo-W-xSi laser cladding coating is 1 wt% due to the benefit of enrichment of Mo and Cr in the inner layer resulting in a protective oxides scale and better corrosion resistance while excessive Si (1% < Si ≤ 5%) caused obvious cracks along the network grain boundaries leading to poor corrosion resistance. Corrosion products such as NiS, Cr2S3, MoO2 and other mixed corrosion products were detected and the multi-layer structure of corrosion scales were observed. The formation of outermost sulfide layer and innermost oxide layer was duo to the corrosion of Ni and Mo leading to a selective formation of Ni-S and Mo-O, respectively. The detailed corrosion mechanisms based on the Gibbs free energy principle were discussed in this study.