Study On The Preparation Of 80Ni20Cr/Inconel625 Coating And Its Corrosion Behavior In Synthetic Flue Gas

Waste incineration power generation has gradually replaced the composting and landfill as the first choice for the treatment of garbage because of its obvious comprehensive advantages.However,the process of waste incineration will produce complex flue gas and molten salt,and the hazardous service environment can cause a serious high-temperature oxidation and hot corrosion,so the protection of boiler has become an urgent problem to be solved.In this paper,80Ni20Cr/Inconel625 alloy coating with NiAl and NiCrAlY layer and with 80Ni20Cr content of 10 wt.%,20 wt.%,30 wt.% and 40 wt.% was prepared on the surface of 20# steel by optimized HOVF technique.The bonding strength,hardness,porosity,salt spray resistance,and high temperature oxidation resistance at the 600 and 700 ℃ in simulation environment were tested.The kinetics curves of hot corrosion were obtained by weighting.The phase,microstructure and composition of the coatings and scales were investigated by scanning electron microscope/energy dispersive spectroscope and X-ray diffraction.The mechanism of high temperature corrosion was discussed.The analysis result of microstructure and properties of the coating indicated that: the main phase of 80Ni20Cr/Inconel625 alloy coating was Cr₂Ni₃ and CrNi₃,with the increase of 80Ni20Cr content,the content of CrNi₃ in the coating increased gradually;deposit of the samples is fine and uniform,with a small amount of oxide;t he 80Ni20Cr/Inconel625 alloy coating prepared by the optimized HOVF is dense,The porosity of 80Ni20Cr/Inconel625 alloy coating with NiAl and Ni CrAl Y layer were 0.52% and 0.68%,The average bonding strength between coating and substrate is 56.06 MPa and 49.69 MPa,The average HRB value of coating hardness was 90.80 and 90.28,the average thickness of coating was 342.5μm and 340μm,respectively.The results of neutral salt spray test indicated that: 80Ni20Cr/Inconel625 alloy coating prepared by HOVF has good salt spray resistance,A3 samples with NiAl layer and B1^B4 samples with NiCrAlY layer generate some rust at the border,while the other samples did not corrode obviously after 1000 h salt spray test.All the samples did not fall off and could pass the neutral salt spray test.The porosity of the coating has a great influence on the corrosion resistance of the coatings,coatings with the lower porosity could have a better salt spray corrosion resistance,samples with NiAl layer could have a better salt spray corrosion resistance.High temperature corrosion behavior of HOVF coating in synthetic 25%Na Cl+75%Na₂SO₄ /0.15%SO₂ environment indicated that: All coatings corrosion product were peeled off in the corrosion process of 200 h at 600 ℃,the surface corrosion products are Ni O and a small amount of Ni Cr₂O₄,corrosion products of all samples were stratified,the outer layer was porous and rich in Ni and O,while the inner layer was relatively dense,containing Ni,Cr,O and a small amount of S;samples coated by NiCrAlY layer is easier to generate oxide band at the coating/ substrate interface when corroded.However,when corroded at 700 ℃,corrosion products were main Ni O and Ni Cr₂O₄,a small amount of Cr₂O₃ and Ni₄S₃ was also detected on the sufuce of samples;structure of corrosion products became more complex;the samples suffered heavy losses in the process of corrosion,and the corrosion products were peeled off when the content of 80Ni20Cr was 40 wt.%.Increasing of the content of Cr in the material can improve the resistance to sulfate corrosion,while raising Ni content can improve the high tempetature Chlorine corrosion resistance significantly.High tempetature corrosion resistance of 20%80Ni20Cr+ 80%Inconel625 alloy coating was best,especially the layer was NiAl coating.