The Effect Of Heat Treatment On The Properties Of Zr-based Bulk Metallic Glasses

The main methods to study the properties of amorphous alloys by heat treatment are cryogenic thermal cycling treatment,annealing above glass transition temperature(high temperature annealing),and annealing below glass transition temperature(low tempera-ture annealing),etc.After the above heat treatments,the internal atomic structure and free volume of the Zr-based bulk amorphous alloy will be changed,which will affect the mechanical,thermal and corrosion properties of the amorphous alloy.In recent years,electrochemical etching has been considered as the ideal method for preparing hydro-phobic surfaces,which can be influenced by the corrosion resistance of the sample itself.Heat treatment can influence the corrosion resistance of amorphous alloys and thus have an effect on the preparation of hydrophobic surfaces by electrochemical etching,but no research has been carried out in relation to this.On the other hand,in practical applica-tions,amorphous alloys inevitably suffer from plastic deformation,which affects service life.The deformation leads to a large number of shear bands within the material,and heat treatment of the deformed amorphous alloy in the supercooled liquid phase interval may allow partial recovery of the shear bands,resulting in a structural and energy state within the shear bands that is close to or approximately the same as the original alloy,in order to enhance the mechanical and corrosion resistance of the amorphous alloy to avoid materi-al failure.This paper studies the above two aspects,and the main findings are as follows:(1)Zr₄₈(Cu_5/6Ag_1/6)₄₄Al₈ amorphous alloy can induce the formation of free volume after cryogenic thermal cycling treatment,while annealing treatment can annihilate the free volume.The annealing treatment improved the corrosion resistance of the samples before electrochemical etching,but cryogenic thermal cycling treatment decreased their corrosion resistance.Under the same electrochemical etching conditions,a superhydro-phobic surface was obtained by forming a micro-nanocomposite structure on the surface of cryogenic thermal cycling treatment compared to the untreated specimens,however the annealing treatment decreased the hydrophobic properties of the samples.Electro-chemical experiments showed that the superhydrophobic alloy had outstanding corrosion properties,the hydrophobic and corrosion properties decreased slightly after 7 days of being soaked in 3.5wt%Na Cl solution.In addition,the prepared amorphous alloy su-perhydrophobic surface possessed good resistance to cyclic elastic compression and temperature resistance.(2)High temperature annealing was performed on the deformed Zr₆₅Cu₁₅Ni_12.5Al_7.5amorphous alloy.It was found that at the same annealing temperature,the yield strength of the samples after annealing was slightly lower than that of the samples before anneal-ing.As the annealing temperature increased,the plastic deformation of the annealed samples decreased to 14.5%(643 K for 10 min),9.5%(663 K for 10 min)and 3.0%(683K for 10 min),but still had good plasticity.Thermal experiments showed that as the an-nealing temperature rose,the crystallisation temperature and the width of the supercooled liquid phase interval declined and the thermal properties of the samples were depressed.In 3.5 wt%Na Cl solution,the corrosion properties of the samples after the annealing treatment were all better than before the annealing treatment,but still worse than unde-formed samples,and the corrosion current density of the 663 K annealed alloy was one order of magnitude lower than that after the 683 K annealing treatment.(3)The effect and mechanism of high temperature annealing and low temperature annealing treatment on the corrosion properties of deformed Zr₆₅Cu₁₅Ni_12.5Al_7.5 bulk amorphous alloy after deformation were studied in detail.It was found that the corrosion resistance of the samples after high temperature(643 K)and low temperature(615 K)annealing treatment in 3.5 wt%Na Cl solution was worse than that of the deformed sam-ples,but still not as good as the original corrosion resistance.The corrosion resistance of the samples after 643 K annealing was better than that of the 615 K annealing.The de-gree of corrosion of the sample surface was increased in the order of as-cast,643 K,615K and compression of about 2%.XPS analysis showed that the enhanced corrosion re-sistance after annealing was related to the enrichment of Zr⁴⁺and Al³⁺,and the formation of Zr O₂ and Al₂O₃ on the surface can improve the stability of the passivation film.EDS analysis showed that the content of Cu element was reduced compared to that after low temperature annealing,which was prone to electrical coupling effects on the surface of the sample after high temperature annealing,and the passivating element Zr was in-creased to avoid further contact between the alloy and the corrosion solution.So,the corrosion resistance of the samples after high temperature annealing was better than that after low temperature annealing.