Study On Corrosion Behavior Of Fe-based Amorphous Alloy Without Metalloids

Fe-based amorphous alloys are widely used in various fields because of their excellent mechanical,soft magnetic properties and cost advantages.To improve its glass forming ability,the current method is mainly by adding metal elements such as C,B,P and Si,but most Fe-based amorphous alloys designed by this method have great brittleness and can hardly plastic deformation.By increasing metal bonds and reducing covalent bonds,our research group designed two groups of Fe-based amorphous alloys without metalloid(Fe_0.52Co_0.48-xNi_x)₇₃Cr₁₇Zr₁₀（x=0.06,0.18,0.30）and(Fe_0.52Co_0.48)₇₃Mo_17-xCr_xZr₁₀（x=9,12,17）,and studied their thermal stability,magnetic properties and mechanical properties in detail.In view of its great reference value and potential application prospect,the research on its corrosion behavior and corrosion resistance in service environment can not be ignored.In this thesis,two new components x=0.12 and x=0.24 are added on the basis of(Fe_0.52Co_0.48-xNi_x)₇₃Cr₁₇Zr₁₀.The preparation of FeCoNiCrZr and Fe Co Mo Cr Zr amorphous alloys and their corrosion behavior in 3.5wt.%Na Cl solution are mainly studied.The effects of constituent elements and structural state of Fe-based amorphous alloy on glass forming ability and corrosion performance,the effect of SO₄^2-concentration on corrosion performance and the formation and destruction of passive film were studied.（1）In FeCoNiCrZr amorphous alloy,with the increase of Ni/Co,the glass forming ability firstly increases and then decreases,among which(Fe_0.52Co_0.36Ni_0.12)₇₃Cr₁₇Zr₁₀ is the strongest,△T_x reaches 54.7 K;In Fe Co Mo Cr Zr amorphous alloy,the glass forming ability increases with the increase of Cr/Mo,among which(Fe_0.52Co_0.48)₇₃Cr₁₇Zr₁₀ is the strongest,△T_xreaches 50.1 K.（2）The corrosion resistance of FeCoNiCrZr amorphous alloy increases with the increase of Ni/Co,among which(Fe_0.52Co_0.18Ni_0.30)₇₃Cr₁₇Zr₁₀ is the strongest;The corrosion resistance of Fe Co Mo Cr Zr amorphous alloy firstly increases and then decreases with the increase of Cr/Mo,among which(Fe_0.52Co_0.48)₇₃Mo₅Cr₁₂Zr₁₀ is the strongest.The corrosion resistance of most FeCoNiCrZr amorphous alloy is better than Fe Co Mo Cr Zr amorphous alloy.（3）Cl^-in Na Cl solution destroys the passive film on the alloy surface through polarization,resulting in galvanic reaction between different elements in the corrosion pit,and the elements are selectively dissolved.In FeCoNiCrZr,Fe is dissolved as anode and Ni and Zr are accumulated as cathode;In Fe Co Mo Cr Zr,Fe is dissolved as anode and Cr and Zr are accumulated as cathode.At the same time,in the process of metal element dissolution,O element is constantly involved in the formation of passive film,which effectively prevents the destruction of Cl^-to the passive film and polarization reaction,to improve the corrosion performance of amorphous alloy.The main chemical components of the passive film of FeCoNiCrZr are Fe₂O₃,Fe O,Co O,Co₂O₃,Ni O,Cr₂O₃,Zr O₂.As a passivating element,Ni can significantly promote the formation of the passive film,while Co can promote the enrichment of Zr to promote the stability of the passive film.The main chemical components of Fe Co Mo Cr Zr passivation film are Fe₂O₃,Fe O,Co₂O,Mo O₃,Cr₂O₃,Zr O₂.As a refractory metal element,appropriate addition of Mo can reduce or eliminate the active vacancy on the surface of amorphous alloy and promote the enrichment of Cr in the passivation film,so as to improve the corrosion performance.（4）In the mixed solution with different concentrations of Na₂SO₄ and 3.5wt.%Na Cl,when the concentration of SO₄^2-is lower than 1.0wt.%,the corrosion resistance of the amorphous alloy decreases gradually with the decrease of the concentration of SO₄^2-,it is the worst when the concentration of SO₄^2-is 1.0wt.%.When the concentration of SO₄^2-is higher than 1.0wt.%,the corrosion resistance increases gradually with the increase of SO₄^2-concentration,and it is the best when the concentration of SO₄^2-is 4.0wt.%.（5）The amorphous alloys after structural relaxation are completely amorphous.Structural relaxation can improve the thermal stability of the amorphous alloy,△T_x reaches 61.5 K,reduce the free volume content,make the structure more stable,and the effect of prolonging the relaxation time is better.Crystallization treatment will reduce the corrosion resistance of amorphous alloys,and a certain degree of structural relaxation can inhibit the dissolution of elements and the damage of Cl^-to the passive film,reduce the pitting sensitivity,and improve the corrosion resistance.The effect of 0.5 h and 2 h structure relaxation is the best.