Study Of Ni-Cr Coating Characteristics For Resistant High-temperature Corrosion Of Power Station Boiler

Thermal spraying is an effective way to protect the metal from corrosion and abration.Arc spraying has the advantages of convenient operation and simple craft,while the domestic technology of new type of Ni-Cr coating,which is used to protect the power station boiler,does not have enough testing data to prove its feasibility and its application effects.Arc spraying technology,with the coating materials of PS45,FeCrAl and 4Cr13,is used in this paper on the normal low carbon steel Q235,compared with the widely used material 12Cr2MoWVTiB for the super heater of power station boiler.On the condition of 700℃,experiments of high-temperature oxidation and hot corrosion have been done with discontinuous gravimetric method.Kinetic curves of oxidation and corrosion are obtained,so as the equations of the corrosion velocity.The morphology and microstructure are studied by SEM and EDS of the layer of the coating as well.Results show that,Cr₂O₃ is the main protective film from high-temperature erosion.With concentration of Cr higher up to 45%,PS45 coating can form a continuous and steady protective film,which will benefit quite a lot to the anti-oxidation and anti-corrosion at high temperature.While the anti-corrosion capability of the coatings of FeCrAl and 4Cr13 is very poor.Bonding feature and anti-abrasion ability of three coatings are compared through micro hardness experiments and anti-thermal chock experiments at the temperature of 700℃.Results show that,there are about more than 50%of Ni and 4%Ti in the coating of PS45,while with good Plasticity of Ni,the coefficients of temperature expansion between the coating and the base are very close,so the bonding intensity is strengthened enough in case of the falling off of the coating,so as to get a superior bonding capability. While higher concentration of Cr can be useful to get higher hardness,and also better anti-abrasion capability.Although the bonding feature of the coating of FeCrAl is quite good,the hardness and anti abrasion ability are not high enough.Furthermore,as the reason of higher concentration of carbon,the coating of 4Cr13 is good both at hardness and anti abrasion.As the temperature of the heating surface of the power station boiler can reach up to about 800～1300℃,the ash grains are quite soft,which may have some influence on the abrasion of the heating surface,but quite small,therefore,more attention will be paid on the high temperature corrosion and thermal expansion.Studies in this paper show that, coatings of FeCrAl and 4Cr13 can not meet this need.However,the coating of PS45 with arc spraying technology has the advantages of higher anti oxidation capability and anti corrosion at higher temperature,better bonding feature and anti abrasion as well,can protect the higher temperature heating surface of power station boiler effectively.