Study On Preparation And Properties Of Corrosion Resistant Coating For Water Wall Of 660 MW Ultra Supercritical Boiler

At present,thermal power generation is still the most important form of power generation in China.Boiler,turbine and motor are three main parts of the thermal power plant.Blasting accidents of water-cooled wall tubes account for a large proportion of the accidents of boiler unit.In recent years,in order to meet the requirements of environmental protection,coal-fired power boilers generally adopt the low-nitrogen combustion,but low nitrogen combustion intensifies the reductive atmosphere in the boiler,resulting in high temperature corrosion of the boiler water wall toward the fire side.Therefore,it is an important issue of thermal power technology in China at this stage to find a cost-effective technical scheme for the prevention of high temperature corrosion of the surface of water-cooled wall so as to achieve the key generic technology that has long troubled the thermal power generation industry.This paper chooses supersonic arc spraying technology as the main technical means for the preparation of corrosion-resistant coatings for boiler water wall.Iron-based alloy wire and Nickel-based alloy wire and a new arc spraying material designed and manufactured by ourselves are selected as spraying materials.This paper compares and analyses the micro-structure,porosity and wear resistance of the coatings through the application of Metallographic Microscope,Scanning Electron Microscope(SEM),Energy Dispersive Spectrometer(EDS),X-ray Diffraction Analysis(XRD)and Friction and Wear Testing Machine.Thermal shock test and thermal corrosion test are designed to compare and analyze the thermal shock resistance and thermal corrosion resistance of these three coatings(FeCrNi coating,Ni Cr coating and self-developed coating).The conclusions are as follows:1.It can be found that the metallographic structure of the self-developed coatings is more compact.This is mainly because the self-developed coatings contain B element,a non-metallic element,which can improve the structure compactness of the alloys.The porosity of all kinds of coatings was measured by image analysis method.It was found that the porosity of self-developed coatings was the lowest among the three coatings,only 1.69%.2.The surface hardness of the coatings ranked from large to small is as follows:self-developed coatings>Ni Cr coatings>FeCrNi coatings,and the surface hardness of the self-developed coatings reached 487HV.The high surface hardness of self-developed coatings is mainly due to the effect of B element in self-developed coatings on improving the compactness and strength of the structure.3.According to the wear rate,the order of wear resistance of coatings is:self-developed coatings>Ni Cr coatings>FeCrNi coatings.As far as the wear mechanism is concerned,the wear forms of FeCrNi and Ni Cr coatings are mainly adhesive wear and abrasive wear is paved.The wear form of self-developed coatings are mainly abrasive wear.4.The thermal shock resistance of the coatings ranked from strong to weak as follows:FeCrNi coating>self-developd coating>Ni Cr coating.The thickness of the coating also affects its thermal shock resistance.As for the same coatings,the thicker the thickness,the worse the thermal shock resistance.5.It can be found that the thermal corrosion resistance of the coatings ranks from strong to weak is as follows:Ni Cr coating>self-developed coating>FeCrNi coating.Among the same coatings with different thicknesses,thicker coatings have stronger thermal corrosion resistance.This is mainly because the content of Cr element in Ni Cr coating is the highest among the three coatings.Cr₂O₃ produced by Cr element has excellent corrosion resistance,so Ni Cr coating has the strongest thermal corrosion resistance.