Research On Oxidation Resistance Of Electron Beam Smelting Of Nickel-based 718 Alloy

Nickel-based 718 alloy is a kind of superalloy material which is widely used in the application of aerospace,gas turbine and nuclear power equipment,and so on.Because of its high operating temperature,and being subjected to long-term erosion of the gas or ocean atmosphere,it needs to possess the excellent high temperature oxidation resistance and corrosion resistance to extend the service life of the components as well as guarantee the normal running of the central equipment.The reasearch emphasis of the oxidation resistance and corrosion resistance of nickel-based superalloys are mainly adjusting the content of protective elements in the alloy such as C r,Al,Si and Ti,adding the rare earth elements or oxygen active elements,and depositing the aluminum-rich coatings,and so on,little research is carried out about the effect of alloy purity on the oxidation resistance.In this paper,electron beam smelting technology was used to refine the raw material of 718 alloy,the 718 ingot with high purity was prepared,the oxidation resistance of electron beam smelted 718 alloy and 718 alloy prepared by traditional methods was studied,the grain size,content and distribution of trace impurity elements and the morphology and composition of the oxide film of the two kinds of 718 alloys were analyzed.The oxidation kinetics and oxidation behavior o f two kinds of 718 alloy at 800?,900?,1000? for 120 h were analyzed and compared by using of the static weighting method and various detection methods.It can be seen from the comparative analysis that the oxidation weight gain per unit area of electron beam smelted 718 alloy oxidized at 800?,900?,1000? is lower than that of the vacuum induction melted 718 alloy at the corresponding temperatures.The activation energy of electron beam smelted and vacuum induction melted 718 alloy are Q1=131.86kJ/mol,Q2=53.66kJ/mol and Q1=122.63kJ/mol,Q2=45.37kJ/mol respectively,the electron beam smelted 718 exhibits better excellent oxidation resistance compared with the vacuum induction melted 718 alloy;The composition of the oxide film on the surface of the 718 alloy prepared by electron beam smelting is Al?2O?3,Cr?2O?3,NiCr?2O?4,TiO?2,TiC,Ti?3O?5 and Ni?3(Al,Ti)phase,with the similar composition of the surface oxide film of vacuum induction melted 718 alloy,besides,a small amount of N iO and CoCrO?4 phase are contained;The grain size of the forged 718 alloy prepared by electron beam smelting technology is about 150 ?m,the grain size of the forged vacuum induction melted 718 alloy is less than 20 ?m,consequently,the high density of grain boundary,faster nucleation and growth rate of oxides and obvious oxidation weight increase of unit area could be expected due to the smaller grain size;Besides,it is also shown that the content of impurity elements and the properties of the oxide film affect the oxidation resistance of the 718 alloy.