Crystallization And Corrosion Behaviors Of Zr Based Amorphous Alloys

The glass transition characteristics and crystallization behaviors as the unique properties of amorphous alloys have important significance for studying the formation mechanism of amorphous and glass forming ability besides the influence on the properties of the alloys.Zr-based amorphous alloys and their composite materials have broad application prospects in the fields of biomedicine,chemical industry and nuclear industry,therefore it's especially important to study their corrosion resistance.Although there have been many reports on the corrosion resistance of Zr-based amorphous alloys and their composites,most of the research objects are not comprehensive enough,without control variables or no formed perfect unified theory.In addition,the corrosion behaviors of different alloy systems are not consistent.Therefore,the corrosion behaviors of Zr-based amorphous alloys and their composites in different alloy systems need to be systematically studied.In this paper,Zr₆₀Cu₂₅Al₁₀Ti₅amorphous alloy was successfully developed by copper mold ejection casting,together with Zr₆₀Cu₂₅Al₁₀Fe₅amorphous alloy as the based object.The structure of the alloys were characterized by X-ray diffraction and differential scanning calorimetry,and the thermodynamics of the alloy were obtained.The corresponding isothermal annealling treatment scheme was established after obtaining the thermodynamic parameters of the alloy,then the crystallization behaviors of Zr₆₀Cu₂₅Al₁₀Fe₅and Zr₆₀Cu₂₅Al₁₀Ti₅alloys with different treatment times and temperatures were obtained.After continuous variable temperature annealing treatment for these two alloys,The kinetic behaviors of glass transition and crystallization process were comprehensively studied by Lasocka and Kissinger equations.The kinetic eigenvalues,together with atomic apparent activation energies were obtained,as well as the conclusion of more dependency on the heating rate and better glass forming ability for Zr₆₀Cu₂₅Al₁₀Ti₅alloy.Zr₆₀Cu₂₅Al₁₀Fe₅and Zr₆₀Cu₂₅Al₁₀Ti₅alloy samples with complete amorphous structure,complete crystalline structure and composite structure were prepared by isothermal annealling treatment.These six samples with three structures were tested for corrosion resistance by electrochemical method and immersion method in Na Cl and HCl solution,and the corrosion morphology of the samples surface was observed by scanning electron microscopy.We found that the order of corrosion resistance from good to bad is crystalline Zr₆₀Cu₂₅Al₁₀Ti₅and crystalline Zr₆₀Cu₂₅Al₁₀Fe₅alloys,Zr₆₀Cu₂₅Al₁₀Fe₅and Zr₆₀Cu₂₅Al₁₀Ti₅alloys with composite structure,Zr₆₀Cu₂₅Al₁₀Fe₅and Zr₆₀Cu₂₅Al₁₀Ti₅amorphous alloys.Compared with the completely amorphous alloy,the corrosion rates of the completely crystalline Zr₆₀Cu₂₅Al₁₀Fe₅and Zr₆₀Cu₂₅Al₁₀Ti₅alloys were reduced by 62%and 82%,respectively.In order to study the effects of elements and cooling rate on the microstructure and corrosion behaviors of the alloys,different amounts of Nb and V elements was added to the Zr₆₀Cu₂₅Al₁₀Fe₅alloy,respectively.It was found that with the increase of Nb amount,the alloy gradually precipitated the second phase with crystalline structure,and the corrosion resistance was gradually improved.The addition of V element deteriorated the glass forming ability,and precipitated crystal phase even if a small amount addition.The corrosion resistance decreased with the increase of V content.The decrease of cooling rate reduced the atom arrangement chaotic degree,improved the crystallization tendency and corrosion resistance of Zr₆₀Cu₂₁Al₁₀Fe₅Nb₄and Zr₆₀Cu₂₁Al₁₀Fe₅V₄alloys.