Investigation On Pitting Behavior Of N5 Nickel-based Superalloy Nanocrystalline Film By Magnetron Sputtering

The nanocrystalline film material prepared by the magnetron sputtering technology has superior corrosion resistance compared with the coarse crystal material of the same composition.In previous studies,it was found that material nanocrystallization can affect its pitting resistance.The study uses macroscopic testing methods to illustrate the overall corrosion law of the material,but lacks an in-depth exploration of the microscopic angle of the pitting behavior of nanocrystalline materials.Therefore,the experimental studied the pitting corrosion behavior of a conventional coarse-grained N5 nickel-based superalloy and a sputtered nanocrystalline film material of the same composition in a 3.5%NaCl aqueous solution at room temperature.In-situ and continuous observations were carried out by traditional electrochemical test methods combined with atomic force microscopy.The pitting corrosion behaviors of the two materials from pit initiation,metastable pit to stable pit were studied in depth.Reveal the pitting corrosion behavior of the two materials.To provide a theoretical basis for improving the pitting resistance of nickelbased alloys.The two materials were subjected to constant potential polarization.The N5 coarse-grained materials were observed by scanning electron microscopy and the N5 sputtered nanocrystalline thin film materials were in situ and continuously observed by atomic force microscopy.It is found that the pitting initiation of N5 coarse-grain nickel-base superalloy is preferentially dissolved by the inclusion of Ta-rich phase.The N5 sputtered nanocrystalline film material is formed by the uniform distribution of internal elements,which causes the pitting initiation position to change to the boundary of flocculent passivation particles.Combining the stochastic theory with the statistical analysis method of potentiostatic polarization data,it is found that the occurrence rate of metastable pit events of sputtered nanocrystalline thin film materials is higher than that of coarsegrained N5 nickel-based superalloy,however,the passivation films of sputtered nanocrystalline films are continuous and uniform.It has a strong metastable pit selfrepairing ability and inhibits the transition from metastable pitting to stable pit.Using the results of the potentiostatic polarization curve,the statistical analysis of the formation process and growth process of the stable pit of the two materials in 3.5%NaCl solution showed that the sputtering nanocrystalline film material inhibited the stable pit relative to the coarse crystal N5 material.The pit shapes of the two materials were observed and counted.The results show that the morphology of the stable pit of the coarse-grained N5 alloy is semi-elliptical,while the material of the sputtered nanocrystalline film is shallow dish.The stable pit growth mechanism of the sputtered nanocrystalline thin film material is different from that of the coarse crystal material and has better corrosion resistance.