Surface Modification,Microstructure And Properties Of Nickel-based Superalloy GH80A And GH3039 Treated By High-current Pulsed Electron Beam

In this paper,the"HOPE-1"type high-current pulsed electron beam?HCPEB?device was used to irradiate the surfaces of nickel-based superalloys GH80A and GH3039.The samples of two systems were irradiated with 5,10 and 20 pulses.The microstructure on the irradiated surfaces of specimens were characterized in detail.The resistance to high temperature oxidation was tested by the static oxidation discontinuous weighing method.For the initial and 20-pulsed samples,the oxidation products of 1 h and 100 h were characterized by SEM.In addition,the electrochemical workstation was used to test the corrosion resistance,and the surface modifying mechanisms were discussed based on the results of microstructure characterizations.After HCPEB treatment,the result of XRD analysis showed that no new phase formed on the surfaces of both GH80A and GH3039 superalloys,and the?/???111?diffraction peak of GH3039 was significantly widened,which according to Scherrer formula,implied that the grain refinement occurred after HCPEB irradiation.The?100?and?110?diffraction peaks of??(Ni₃?Al,Ti?in initial GH80A disappeared after irradiating indicating that??phase was dissolved,and the same time,Ni,Al and Ti elements were dissolved into the matrix forming a super-saturated solid solution.It can be inferred that the sample composition homogenized after irradiating.After irradiating,all surfaces formed a typical crater,which gradually disappeared with the increase of irradiation times.Both the GH80A and GH3039 alloy melted,a large amount of dislocation slip was formed on the surface of the samples.For GH80A alloy,the grain size of 20-pulsed sample was found about 3?m,while the GH3039 alloy 20-pulsed sample's grain size was found about 5?m,which means that the grain refinement was induced by HCPEB treatment.After 20 pulses,the thickness of the remeled layer formed on the GH80A surface was found about 3?m,which further evidenced the remelting has occurred.HCPEB irradiation formed high density deformation twins.From the results of high-temperature oxidation test,the high temperature oxidation performance of both GH80A and GH3039 were significantly improved after 20-pulsed irradiation,which improvements were due to grain refinement,composition homogenization,the formation of diffusion paths for Cr and the hindered transformation of Cr₂O₃ oxide film to volatile chromium oxide,and all these mechanisms resulted in a formation of a dense protective Cr₂O₃ oxide film.From the results of corrosion test,the corrosion current density of the samples irradiated by HCPEB decreased as compared with that of the initial samples.The20-pulsed sample demonstrated the minimum corrosion current density,and the corrosion voltage of 20-pulsed sample was found higher than that of the initial samples.The improvement of corrosion resistance was essentially attributed to several factors.First,the microstructure of the sample surfaces became uniform after irradiating.Secondly,the electrochemical characteristics of the sample surfaces tended to become consistent.Thirdly,the high-density microstructural features formed inside the alloys promoted the formation of corrosion-resistant passivation film.Therefore,the corrosion resistance was eventually improved.