The Preparation Of FeAl-Al Intermetallic Composite Coatings And Study On High Temperature Erosion And Hot Corrosion Resistance Of The Coatings

The FeAl intermetallic compounds have a long-range and orderly special structure,so they have many excellent properties,such as good high temperature oxidation resistance,excellent sulfidation corrosion resistance,high specific strength,etc.,and at the same time,they have low density and low cost.The advantages are expected to solve the problem of high temperature erosion and hot corrosion protection of circulating fluidized bed boilers.In this dissertation,FeAl-Al coatings with dense structure and uniform composition are prepared by High Velocity Oxygen Fuel?HVOF?.The research focuses on the erosion wear and the The hot corrosion behavior provides a theoretical basis for the final development of high temperature anti-erosion and hot corrosion coatings suitable for the protection of circulating fluidized bed boilers.The main content and results are as follows.The main points of this thesis are summarized as follows:The spray powder feed was designed,and 5% and 10% aluminum powder were added to the iron-aluminum alloy powder feed,respectively.FeAl-Al intermetallic compound coatings with a thickness of 150?m were prepared by supersonic flame spraying Floor.Compared with FeAl coating,adding Al powder to the powder feed can obviously improve the supersonic flame spraying effect,and obtain a coating with dense structure and strong bonding with the substrate.With the addition of 5%Al powder,the coating surface was densely packed with molten particles,no obvious holes and cracks were found,and the structure of some areas was very uniform.With the addition of 10% Al powder,a large amount of Al elements in the coating aggregated,and aluminum elemental aggregation occurred.Heat treatment can further improve the microstructure of the coating.Appropriate heat treatment temperature can further eliminate spray defects,make the microstructure of the coating denser and increase the microhardness.The sprayed FeAl,FeAl-5Al,and FeAl-10Al coating phases are all Fe₂Al₅.With the increase of the heat treatment temperature from 500? to 800?,the intensity of diffraction peaks of the Fe₂Al₅phase gradually increase and the crystallinity of the coating is improved.When the heat treatment time increased from 2h to 6h,FeAl-5Al coating was more uniform and denser,and more FeAl intermetallic compounds were formed.The effect of erosion temperature,erosion abrasive grain flow and erosion angle on the high-temperature erosion performance of FeAl-Al coatings was studied using a trial-built gas-solid high-temperature erosion wear tester.The microstructural changes and erosion behavior were investigated in details by means of Scanning Electron Microscope?SEM?.The erosion rate of FeAl-Al coating was 5.36 mg/kg at room temperature,and the weight loss was mainly caused by brittle spalling and ploughing.With the increase of erosion temperature,the erosion ability of FeAl-Al coating increased.The erosion resistance was the best at an erosion temperature of 500?,and the erosion rate was only 1.86 mg/kg.With the increase of abrasive particle flow,the damage degree of the coating surface gradually increased,and the erosion rate was the largest at 0.5 kg,which was 4.62 mg/kg.The erosion behavior of FeAl-Al coating is a typical plastic erosion.The erosion rate is the highest at an erosion angle of 45°,which is 5.29 mg/kg.When the erosion angle is 90°,the erosion is mainly plowing and microcutting.When the erosion angle is 30°,the erosion is mainly cutting.The hot corrosion performance of FeAl-Al coatings was studied.The hot corrosion of 75% NaSO₄/25% NaCl molten salt at 500? was found.The FeAl-5Al coating has excellent hot corrosion resistance,and its hot corrosion model belongs to low temperature hot corrosion.model.The surface phase of the coating is Fe₂Al₅ and a small amount of Al₂O₃.The thermal corrosion effect is similar to that of heat treatment.The defects in the coating are reduced and the structure is more dense.When the thermal corrosion temperature was increased to 700?,a small amount of fine cracks appeared on the coating after 2 hours of thermal corrosion,and a small amount of Al₂O₃ appeared on the surface.As the thermal corrosion time increased,the thickness of the surface oxide film increased.When the corrosion time was 6 hours,the thickness of the oxide film was about 80?m.