Electrochemical Corrosion Behavior Of Fe-50Ni Alloy With Different Microstructures

Nanocrystalline metal materials have emerged in many fields due to their unique properties.The corrosion question of nanocrystalline metal materials must be solved firstly before they are applied.Therefore,it is of great significance to study the corrosion mechanism of nanocrystalline metal materials in various solutions,to clarify the causes of corrosion,and to take effective protective measures.So far,some researches on the corrosion behavior of nanocrystalline materials at home and abroad have mainly focused on the resistances of surface coatings,while the studies on the corrosion properties of bulk nanocrystalline alloys are especially rare.This paper mainly studies the preparation and corrosion properties of nanocrystalline binary two-phase Fe-Ni alloy.After a large number of experimental optimizations,two nanocrystalline Fe-50Ni alloyed powders were prepared by the liquid phase reduction and mechanical alloying method,respectively.The coarse grained Fe-50Ni alloyed powder was prepared by the powder metallurgy method.Three corresponding nanocrystallineand coarse grained bulk Fe-50Ni alloys were prepared by vacuum hot pressing technology.The electrochemical corrosion data of nanocrystalline and coarse grained Fe-50Ni alloys were measured by electrochemical workstation.The corrosion properties and the effect of grain refinement on their corrosion resistances of three Fe-50Ni alloys were studied in Cl^-containing solutions,acidic solutions and acidic Cl^-containing solutions.The following conclusions have been obtained.?1?After adding NaCl,H₂SO₄ and acidic NaCl solutions to the neutral Na₂SO₄ solution and the corresponding increase of their solution concentrations,the self-corrosion potentials of three bulk Fe-Ni alloys increase.In the same concentration solutions,the self-corrosion potentials increase in the range of the coarse grained PM Fe-50Ni alloy,nanocrystalline MA Fe-50Ni alloy,and nanocrystalline LPR Fe-50Ni alloy.Self-corrosion potentials are positively shifted,indicating that the corrosion tendencies of these alloys increase after the grain refinement.?2?After adding NaCl,H₂SO₄ and acidic NaCl solution to the neutral Na₂SO₄ solution and the corresponding increase of their solution concentrations,the corrosion current densities of the three bulk Fe-50Ni alloys increase,and therefore their corrosion rates also increase.When the solution concentrations are similar,the corrosion rates decrease in the range of the nanocrystalline LPR Fe-50Ni alloy,nanocrystalline MA Fe-50Ni alloy,and coarse grained PM Fe-50Ni alloy.These also show that the nanocrystallization accelerates the alloy corrosion rates.?3?After adding NaCl,H₂SO₄ and acidic NaCl solutions to the neutral Na₂SO₄ solution,Electrochemical impedance spectroscopy?EIS?of three bulk Fe-50Ni alloys are composed of a single capacitive arc without diffusion tail.As the solution concentrations increase,the charge transfer resistances of three bulk Fe-50Ni alloys decrease.When the solution concentrations are similar,the charge transfer resistances increase in the range of the coarse grained PM Fe-50Ni alloy,nanocrystalline MA Fe-50Ni alloy,and nanocrystalline LPR Fe-50Ni alloy.This is consistent with the conclusions gotten from the potentiodynamic polarization curves.?4?In neutral Na₂SO₄ solution,0.3 mol/L NaCl solution,0.30 mol/L H₂SO₄ solution and NaCl solution?pH=2?were added.According to the Arrhenius formula,the average activation energy of three Fe-50Ni alloys decrease in the range of the coarse grained PM Fe-50Ni alloy,nanocrystalline MA Fe-50Ni alloy,and nanocrystalline LPR Fe-50Ni alloy.This indicates that PM Fe-50Ni alloy has the slowest dissolution rate and the best corrosion resistance,MA Fe-50Ni alloy is followed,and finally LPR Fe-50Ni alloy has the fastest corrosion rates.This is consistent with the conclusions obtained from the previous potentiodynamic polarization curves.