Effect Of Impurities On Formation And Properties Of Super-Multicomponent Zr-based Bulk Metallic Glasses

Zr-based bulk metallic glasses have higher elasticity,strength,hardness,corrosion resistance and other excellent performances compared to traditional crystalline materials,which implies great potential as structural materials.However,the production of Zr-based bulk metallic glassesare extremely sensitive to impurities in low purity Zr raw material,thus this series of metallic glasses must be prepared using high-purity raw materials under rigorous control of fabrication conditions.Therefore,the extensive applications of Zr-based bulk metallic glasses have been greatly inhibited.Recent studies have shown that super-multicomponent Zr-based bulk metallic glasses can effectively reduce the negative influences of impurities on their glass forming ability and performances,which is very promising for further applications.However,the mechanism of impurity on its glass forming ability and performance is still ambiguous.In this paper,a super-multicomponent Zr50Cu25Al10Ni7Ti4Co2Fe1Y1 bulk metallic glass was adopted,and the effects of impurities on the glass formation ability,thermal stability,mechanical properties and corrosion resistance of this super-multicomponent Zr-based bulk metallic glasses were studied by adding different mass fractions of low-purity Zr raw materials(sponge Zr).Firstly,we considered the width of the supercooled liquid region as the criterion for estimation of glass forming ability of this alloy.DSC analysis was carried out on super-multicomponent Zr-based bulk metallic glasses prepared by different impurity concentrations.The result shows that impurity content has no obvious effect on the glass formation ability of this super-multicomponent Zr-based bulk metallic glasses.Moreover,ingots of this alloy with 20 mm in diameter were fabricated by arc melting.The fractured ingot shows a typical morphology of metallic glass,and the XRD results show that the ingot has a low degree of crystallization and exhibits good glass forming ability.Moreover,we studied the thermal stability and crystallization behavior of super-multicomponent Zr-based bulk metallic glasses prepared by sponge Zr with different concentrations.It is found that the impurity has no obvious effect on the thermal stability of the alloy by DSC curve analysis.But the impurities would affect the crystallization behaviors of the super-multicomponent Zr-based bulk metallic glasses.With the increase of impurity concentration,the crystallization process of this super-multicomponent bulk metallic glasses shows higher complexity and takes longer time.The final crystallization products of the alloys that prepared with different mass fraction impurities were analyzed.The result shows that the impurity content does not affect the crystallization products of the amorphous alloys,and these precipitated phases exhibit crystal structures similar to CuZr2,Cu10Zr7 and a variety of ZrAl phases.Finally,we investigated the mechanical and chemicalproperties of super-multicomponent Zr-based metallic glasses prepared by sponge Zr with different contents.By room-temperature quasi-static compression test,the result shows that super-multicomponent Zr-based bulk metallic glasses have high strength and hardness,but different content of impurities would have various influences on plasticity of this alloy.Low impurity content would not lead to brittleness of the alloy,and their plasticity values are similar.Under the condition that the mass fraction of sponge Zr reaches ?80%,its plasticity increases to 6.7%,which is almost two times higher than the alloy prepared by high purity raw materials under the same casting method.Impurities would lead to the precipitation of in-situ nanocrystals with about 5 nm in diameter in the glassy matrix,and these nanocrystals lead a significant increase in the plasticity.In addition,the super-multicomponent Zr-based bulk metallic glasses containing high content of impurities show decrease in plasticity after low-temperature relaxation,while the ones containing low concentrations of impurity show significant increase in plasticity after the low temperature relaxation.This may be due to the low impurity content in the super-multicomponent Zr-based bulk metallic glasses would cause the increase in compositional heterogeneity in the low temperature relaxation,while the positive effects of nanocrystals induced by decreases would be drastically reduced with the decrease of free volume in the super-multicomponent Zr-based bulk metallic glasses containing high content of impurities.The result of electrochemical corrosion test exhibits that the content of impurities has no significant effects on the self-corrosion potential of the super-multicomponent Zr-based bulk metallic glasses.This means that impurities in low-purity Zr raw material are not important factors on the corrosion resistance of the super-multicomponent Zr-based bulk metallic glasses.