Influence Of Grain Refinement And Ni Addition On Corrosion Electrochemical Properties Of Fe-20Co-20Cr Alloys

Nanometer metallic materials such as nanocrystalline materials,nano-twinned materials,and nano-layered structural,gradient nanostructural as well as composite nanostructural materials have many excellent properties because they have unique microstructure with very high interface densities.Compared with traditional metallic materials,properties of nanocrystalline metallic materials have been improved significantly in many aspects such as specific heat,specific strength and plastic deformation,and so on.The corrosion property is one of the important factors affecting the service life of nanocystalline materials.Therefore,in order to improve the corrosion resistance of nanocrystalline materials,we need to systematically study the corrosion properties of nanocrystalline materials in different solutions,explore their corrosion mechanism,and take technical controlling measures to inhibit the corrosion rates of nanocrystalline materials,thus supplying very useful help for the practical use of nanocrystalline materials.In this paper,the nanometer size MA Fe-20Co-20Cr-20Ni bulk alloyed was obtained through hot pressing the corresponding alloy powders prepared by mechanical alloying（MA）method.The conventional size PM Fe-20Co-20Cr-20Ni bulk alloy was prepared by powders metallurgical（PM）technique.The corrosion electrochemical properties of quaternary PM and MA Fe-20Co-20Cr-20Ni alloys prepared at present and ternary PM and MA Fe-20Co-20Cr alloys prepared earlier were tested by electrochemical workstation,and the influence of nanocrystallizations and element Ni addition on the corrosion electrochemical properties of Fe-20Co-20Cr bulk alloys was studied.The main research results are as follows:PM and MA Fe-20Co-20Cr-20Ni bulk alloys with densities of more than 98%were obtained by hot pressing mechanical alloying and powder metallurgical processes,in which the grain size of MA Fe-20Co-20Cr-20Ni alloyed powders is 11.3 nm,and that of the corresponding bulk alloy is 14.3 nm.Both PM and MA Fe-20Co-20Cr-20Ni alloys are composed of two phases,and the microstructure of MA Fe-20Co-20Cr-20Ni alloy is more uniform than that of PM Fe-20Co-20Cr-20Ni alloy.In H₂SO₄and Na Cl media,the corrosion changes of Fe-20Co-20Cr-20Ni and Fe-20Co-20Cr alloys are similar.In the same concentration H₂SO₄and Na Cl solutions,the corrosion current densities of MA Fe-20Co-20Cr-20Ni/Fe-20Co-20Cr alloys are higher than those of PM Fe-20Co-20Ni/Fe-20Co-20Cr alloys,and the charge transfer resistances and average activation energy are lower than those of PM Fe-20Co-20Cr-20Ni/Fe-20Co-20Cr.Therefore,the corrosion resistances of MA Fe-20Co-20Cr-20Ni/Fe-20Co-20Cr alloys are weaker than those of PM Fe-20Co-20Cr-20Ni/Fe-20Co-20Cr alloys.The corrosion rates of Fe-20Co-20Cr-20Ni and Fe-20Co-20Cr alloys are different.The corrosion rates of PM and MA Fe-20Co-20Cr-20Ni alloys are obviously lower than those of PM and MA Fe-20Co-20Cr alloys at the same concentration H₂SO₄and Na Cl solutions.It can be seen that the added 20 at.%Ni can reduce the corrosion rates of Fe-20Co-20Cr alloy.The corrosion rates of Fe-20Co-20Cr-20Ni and Fe-20Co-20Cr alloys are different in the different corrosive media.The corrosion resistances of Fe-20Co-20Cr-20Ni and Fe-20Co-20Cr alloys in H₂SO₄media are higher than those in Na Cl media.Therefore,Fe-20Co-20Cr-20Ni and Fe-20Co-20Cr alloys in Na Cl media have the better corrosion resistances than those in H₂SO₄ media.