Investigation On Corrosion Behavior Of Zr-based Metallic Glass

Zr-based metallic glasses possess high application value and broad application prospects in the biomedical field because of their high forming ability,excellent mechanical properties,corrosion resistance,good biocompatibility and easy processing.In view of this,this paper studies the corrosion behavior of Zr-based metallic glass in NaCl-containing solutions and NaF-containing solutions,and explores the effects of different solution conditions on the corrosion behavior and mechanical properties.The effect of doping valve metal elements on Zr-based amorphous alloys is studied.Due to the influence of alloy corrosion,Zr-based amorphous components with higher amorphous forming ability,corrosion resistance and biocompatibility have been developed.This article mainly includes the following parts:Standard electrochemical methods were used to characterize the different corrosion behaviors of Zr52Al10Ni6Cu32(abbreviated as Zr52)metallic glass in NaCl and NaF solutions.It is found that metallic glass underwent pitting corrosion in Cl--containing environment,and uniform corrosion in F--containing environment.This is due to the loose bond between Cl-and the surrounding water molecules,which can pass through the passie film and accumulate on the substrate/film boundary,leading to subsequent lattice distortion and pitting corrosion.However,F-is not able to penetrate the passive film due to its strong bond with water molecules,which causes a large amount of F-to be adsorbed on the outside of passive film and form a compound with Zr4+.This process results in the formation of a dense Na3ZrF7layer on the surface of the alloy,which would slows the anode process.The corrosion behavior of Zr52 metallic glass in Na2SO4 solution with different pH and NaF concentration was investigated.The relationship between critical pF and pH has been established.The relationship between the two can be divided into two parts:stable area and unstable area.Zr52 metallic glass maintain a low corrosion rate in the stable area,which provides a reference for judging the corrosion state of the Zr52 metallic glass in F--containing solution.The destruction mechanism of the passive film in the anodic polarization process depends on the pH and NaF concentration.When at high pH and high NaF concentration,a large amount of F-will participate in the formation of passive film and form corrosion products based on ZrF4 with Zr4+,thereby hindering the formation of ZrO2 passivation film.At low pH and low NaF concentration,due to the increase of H+concentration,the dissolution rate of the passive film will increase,and the F-concentration is not enough to form the Zr-F compound,which only destroy the integrity of the passive film.The changes in the mechanical properties of Zr52 metallic glass after immersion in two different concentrations of acidic phosphate fluoride(APF)were studied.The decrease in compression performance is relatively small,and the decrease in tensile performance is relatively large,especially in 0.2%APF solution.The experimental results suggest that when immersed in 0.2%APF solution,a large amount of H atoms enter the alloy matrix through reduction reaction.The Zr atoms are embedded in the interstitial position of the tetrahedron,and the reduced H recombines at the defect position to form H2.Cracks form when H-aggregated defects are located near the surface.The application of tensile stress will cause the alloy to brittle fracture along such cracks.Besides,the dissolved hydrogen will increase the distance between the transition metal atoms,reduce the bonding force between the atoms and the surface energy,finally resulting in brittle failure.The effect of doped valve metals Ti and Nb on the corrosion resistance of Zr51.3Al10Ni6Cu31.8Ag0.1Y0.8(abbreviated as ZY)metallic glass was investigated,and it was found that its corrosion resistance increased.The doped Ti and Nb not only participate in the passivation during the corrosion process,but also increase the content of Zr oxide in the passive film.This is because the doped Ti and Nb form a new combination with Ni and Al in the amorphous matrix,thereby weakening the metal bond between Zr and other components,promoting the dissolution of Zr,and forming a higher proportion in the passivation film ?oxide.This composite passive film has stronger corrosion resistance than the film with a single oxide film.Compared with doped Ti,Nb-doped Zr-based metallic glasses have better corrosion resistance.On the basis of Zr53.6Al18.6Co27.8(abbreviated as ZC),the series of metallic glasses of ZCA with higher glass forming ability,compressive mechanical properties and corrosion resistance were prepared by doping with Ag.Among them,with 2 at.%Ag doped,the maximum diameter of ZCA2 reach 6 mm.Ag element,as a similar element of Co,can replace each other's position in the Zr-Co cluster,which improves the degree of cluster topological packing.From the perspective of mixing entropy,Ag can also increase the degree of confusion in the system,reduce the possibility of precipitation of crystalline phases,thereby enhancing the ability to form amorphous.The compressive fracture strength of ZCA series of amorphous alloys is above 1700 MPa,which is higher than ordinary titanium alloy.With the increase of Ag content,the corrosion resistance of ZCA series amorphous in artificial saliva and PBS solution increases.This is due to the decrease of ZrO2 content and the increase of Al2O3 content in the passive film due to the doping of Ag.This passive film exhibited better corrosion resistance in solution containing both PO43-and Cl-.The biocompatibility of ZCA2 metallic glass compared with TC4 titanium alloy,and it is found that ZCA2 has stronger biocompatibility in the short term,but further investigation is still needed for long-term effect.