The Electrochemical Corrosion Behavior Of Nanocrystalline Bulk Fe-50Cu Alloys

As a new type of materials,nanocrstalline materials have unique properties,which have great potentials in many applied fields.Corrosion as an important factor which affects the service life of materials,is also a standard to measure the materials performance.Studies on physical and chemical properties of nanocrystalline materials have been reported,but there are few studies about corrosion behavior.The majority of the sudies are focus on nanocrystalline coatings and films,but studies about corrosion behavior of bulk nanocrystalline alloys are very rare.Coarse grained and nanocrystalline Fe-50Cu alloy powders were prepared by three different preparation methods,i.e.powder metallurgy?PM?,mechanical alloying?MA?and liquid phase reduction?LPR?.The grain size of alloyed powders prepared by mechanical alloying method is 9.4 nm,and the grain size of alloyed powder prepared by the liquid phase reduction method is 14.6 nm.The bulk nanocrystalline Fe-50Cu alloys were obtained by hot pressing the nanocrystalline alloyed powders synthesized by above methods.The grain size of bulk alloys is still in nanometer range.The corrosion properties of three bulk Fe-50Cu alloys were investigated in neutral NaCl,H₂SO₄ and NaCl acidic solutions by means of electrochemical appratus through open circuit potentials,potentiodynamic polarization,electrochemical impedance spectroscopy and so on.The effect of microstructures was investigated by means of XRD and EDS.In neutral NaCl and H₂SO₄ solutions,the corrosion current densities of three alloys increase with the increment of the concentrations of NaCl and H₂SO₄ solutions.In two solutions,the electrochemical impedance spectroscopies of three Fe-50Cu alloys are composed of a single capative loop without diffusion tails.The change trend of charge transfer resistances of three Fe-50Cu alloys is adverse to that of corrosion current desities.In the same concentration of NaCl soluions,the corrosion current density of MA Fe-50Cu alloy is the largest and its corrosion rate is the fastest.The transfer resistance of PM Fe-50Cu alloy is the largest and its corrosion resistance is the best.In the same concentration of H₂SO₄ solutions,the corrosion current density of LPR Fe-50Cu alloy is the largest and its corrosion rate is the fastest,the transfer resistance of PM Fe-50Cu alloy is the largest,which corrosion resistance is the best.It is found that the activation energy of MA Fe-50Cu alloy is the lowest in NaCl solution after calculating activation energy by using Arrhenius.In H2SO4 solutions,the activation energy of LPR Fe-50Cu alloy is the lowest,which is accord with the conclusions of polarization curve.In the acidic NaCl solutions,the corrosion current densities of three alloys decreases,and the transfer resistance increases with the pH increase.The corrosion current density of MA Fe-50Cu alloy is the largest,the transfer resistance of PM Fe-50Cu alloy is the largest.The activation energy of the MA Fe-50Cu alloy is the smallest through the calculation of the Arrhenius formula.