Formation And Evolution Of Sulfide Scale Of Centrifugal Compressor Blades

The centrifugal compress blade material FV(520)B’s sulfidation resistant property gets more and more attention due to the exploitation of nature gas with high content of H2S.Study on sulfidaiton mechanism of FV(520)B helps to predict the residual life and to be beneficial both theory and practice of development of new sulfidation-resistant alloy with better performance.The influence of each element and growth mechanism of sulfide scale was explained by analyzing of sulfide scales in different sulfidation stage. The defect type of sulfides was illustrated by the analysis of the valance distribution of elements in sulfides by the application of XPS technology. The structure and composition of sub-layers were analyzed by using XRD, SEM, EDS, OM technology to further clarify the growth mechanism and evolution of sulfide scale. The repair of specimen covered by sulfide scale was preliminary discussed by the use of thermal spray technology and the plasma spray technology.The experiment results elucidate that single-layer sulfide scale of600nm was formed after12h sulfidation.XPS data indicated that the scale was mainly consisted of Fe7S8,FeS2,Ni(1-x)S,Cr2S3was found when sputter depth comes to350nm and the concentration of Cr2S3increased with the significant increase of sputter depth.XPS data indicated that the average content of Fe3+and Ni3+found in Fe7S8,FeS2,Ni(1-x)S was36.53%and35.78%,32.08%which drew an conclusion that there were18%cation vacancies in lattice and made it clear that the growth of sulfide scale depended on outward migration of cations. Fe7S8, FeS2, Fe(1-X)S,Cr2S3After120h sulfidation a multilayered sulfide scale was formed with an out layer of (Fe0.5Ni0.5)0.96S, Fe(1-x)S, intermediate layer of only Fe(1-X)S and inner layer of Cr2S3with few Fe(1-X)S. The growth mechanism could be explained as follows:at first stage the sulfide scale was formed by ferrous and nickel sulfide with higher sulfidation rate and finally produced (Fe0.5Ni0.5)0.96S.Then the diffusion rate of Ni2+decreased with the growth of scale due to low content in matrix and the intermediate layer was created by the outward diffusion of Fe2+.The inner layer was formed by the migration of Cr3+reacting with ferrous and nickel sulfide to produce the Cr2S3with little Fe(1-X)S.The repair of specimen covered by sulfide scale was preliminary discussed by the use of thermal spray technology and the plasma spray technology, the results showed that the coating which was produced by thermal spray technology were bonded to substrate badly, partly combination was observed when the sulfide scale is thin. The result of repairing the specimen covered with sulfide scale by using Plasma spray technology is effective, but in the welding region and the binding region sulphide inclusions and pores still existed.