Study On Corrosion Behavior In Simulated Flue-gas/coal-ash Environment Of Several Kinds Of Coatings Prepared By Thermal Spraying

High temperature corrosion behavior and corrosion mechanism of three kinds of austenitic steels?T12?T91?Super304H?and spray three kinds of coatings?45CT?NiCr/Cr₃C₂?NiCrAlY?at 650 and 750?was studied in the synthetic flue-gas/coal-ash environments.These three kinds of coatings prepared by the optimized HVOF is dense,the porosity of these coatings between 0.76%and0.92%.The kinetics curves of hot corrosion and coating thickness change bar chart were obtained by weighting and coating thinning.The microstructure and composition of the scales were investigated by scanning electron microscope/energy dispersive spectroscope and X-ray diffraction.The influence of material composition and temperature,atmosphere and corrosion medium on the corrosion behavior was investigated.The corrosion results of these three steels?T12?T91?Super304H?in flue-gas/coal-ash environments show that,a lot of iron and chromium oxides are formed on the surface of austenitic steels,which are closely related to composition and elements of steels.The higher Cr content in the alloy,the more corrosion resistance in the scale.T12 contains no Cr element,the main products of T12 is Fe₂O₃.the main products of T91?Cr 8.5wt%?is Fe₂O₃ and NiFe₂O₄.In Super304H?Cr18wt%?the corrosion products is mainly iron oxides?Fe₂O₃ and NiFe₂O₄?.as the Cr content is high.The comparison of three kinds of austenitic steels corrosion properties indicate that Super304H is better than T91 and T12.The three kinds of steels all generate little sulfides in affected zone.The corrosion of the steels is mainly oxidation corrosion with light sulfidation in metal/scale interface and internal sulfidation in Substrate under the scale.The sulfidation accelerates destroy the oxide film and enhance the corrosion.The corrosion results of these three coatings?45CT?NiCr/Cr₃C₂?NiCrAlY?in flue-gas/coal-ash environments indicate that,The higher Cr content in the alloy,the more corrosion resistance of the material.The comparison of three kinds of coatings corrosion properties indicate that 45CT>NiCrAlY>Ni Cr/Cr₃C₂.From the corrosion layer thickness,The layer of corrosion product on the surface of the 45CT is thinner than NiCrAlY and NiCr/Cr₃C₂.The surface corrosion products of 45CT are Cr₂O₃?NiCr₂O₄?FeCr₂O₄.The surface corrosion products of NiCr/Cr₃C₂ are NiO?NiFe₂O₄and Fe₂O_3.The surface corrosion products of NiCrAlY are NiFe₂O₄ and Fe₂O₃.Different coatings corrosion product were generate holes and peeled off in vary degrees,The scale of corrosion products had duplex microstructure,The outer layer was rich in Fe?Cr?O,and the inner layer was rich in Ni and O.The T91 steel can be seen to have intergranular corrosion tendency in the substrate after spraying the coating.The T91 steel without coating has a rapid corrosion rate and no tendency to intergranular corrosion.Super304H shows intergranular corrosion morphology without spraying the coating.Samples coated by three coatings is easier to generate oxide band at the coating/substrate interface when corroded.In the corrosion process of Super304H spray coating,the coating/substrate interface corrosion occurred mainly on the side of the coating,while the corrosion of process of T12 and T91 spray coating occurred mainly on the substrate side.