Study On Corrosion Mechanism Of K418 Nickel Base Alloy In High Temperature Molten Salt

Casting K418 is austenitic nickel-based superalloy ? phase as the base,?? phase for precipitation strengthening phase,(?+??)eutectic phase,carbide and boride consisting of a cast nickel-base superalloy.It has strong resistance to oxidation and corrosion resistance.People in order to expand the application scope of nickel-based superalloy,the performance of the nickel base superalloy put forward higher requirements,such as higher strength,better resistance to oxidation and corrosion resistance,etc.By adding trace elements,such as the adding of rare earth elements,although the adding amount was trace,but can obviously increase the strength and oxidation resistance of the nickel-based superalloy corrosion resistance.Are studied from two aspects: first,through the high vacuum arc melting,was prepared by adding different trace elements in the alloy,Y,Ce was studied in nickel base cast microstructure,hardness,and high temperature alloy K418 in fluoride salt(NaF,LiF,KF)the influence of the corrosive.In this paper,the oxidation of the K418 nickel-based high temperature alloy and the heat corrosion in fluoride salt are studied to explore the oxidation and corrosion resistance of the alloy.Test process on the one hand,the main research the K418 nickel base superalloy casting defects,vickers hardness,high temperature oxidation and hot corrosion resistance in high temperature and salt,on the other hand by adding rare earth element Y and Ce and its microstructure morphology,carbide morphology,?? phase,equal(?+??)eutectic and after adding rare earth elements in high temperature oxidation and hot corrosion in salt by experimental research.(1)the addition of trace elements Y,Ce and the addition of Y and Ce elements can reduce the porosity defects in the alloy,refine the grain,and increase the density of the alloy.In addition,also found that the alloy in the form of ?? phase followed Y,Ce add slowly into a ball.The adding of rare earth elements is not the more the better,through hardness test,get started hardness improves with the adding of rare earth elements,instead,continue to add hardness will decline.(2)the participation of salt by accelerating oxidation corrosion of the alloys,and add Y elements,making the presence of a alloy oxidation corrosion layer adhesion,fall off not easily,and the accretion of Ce and Ce with Y add alloy at the same time,the oxide layer are easy to fall off.The accretion of Ce and Ce with Y add alloy at the same time,in the salt corrosion for the corrosion layer,and at the same time,add Y,Ce alloy corrosion degree than alone add Ce nickel-based superalloy.In addition,the internal elements are evenly distributed without the segregation of the Cr elements.(3)separate Y to add,because of oxidation corrosion layer are connected to the matrix,the oxidation corrosion can be continuous,eventually leading to some elements such as Cr,Al diffusion to the surface and the elements distribution non-uniformity,and the outermost layer of Al2O3,Cr2O3 outer layer.(4)the higher the temperature in the high temperature oxidation,the faster the corrosion rate,and the overall appearance of the parabola in the relationship between oxidative weight and time at the same temperature.And in the details,the curve takes a turn,and the corrosion mechanism changes.650? temperature,oxidation,salt is involved,will improve the oxidation rate,and aerobic oxidation of alloy in fluoride salt greatly influence corrosion rate.The oxidative corrosion layer of fluoride is stratified,the outer layer is the oxide of Cr and Al,and the inner layer is the oxide of Cr.