Glass Forming Ability And Properties Of Zr-based Bulk Metallic Glasses

Zr-based bulk metallic glasses(BMGs)have good application prospects owing to their good mechanical properties,superb corrosion resistance and large supercooled liquid region.To develop glass formers with high glass forming ability(GFA)without toxicity element at low cost has been the focus of research for long period of time.However,the GFA of glassy formers is sensitive to compositions,up to this day,as there still lacks an effective method locating good glass-forming compositions.It is always a difficult and hot problem in proposing an effective method to understand the glass formation and develop compositions with high GFA.In this thesis,a method based on the feature of microstructure in amorphous alloys and thermodynamics was proposed to understand glass formation from the view of clusters and entropy of mixing.Under the guidance of this method,a series of Zr-based formers possessing high GFA and a broad application future were developed.This thesis mainly consists of following parts:A method based on clusters and entropy of mixing was proposed to design glass formers.Amorphous alloys were treated as a mixture of clusters.Certain glassy formers were designed by the clusters and the coefficient of clusters.In this thesis,clusters were designed through the features of microstructure and the coefficient was designed through entropy of mixing.A series of classical bulk metallic glasses compositions were verified under the guidance of this method,and the simulation compositions are quite close to those reported in the literature.Further test indicated the simulation compositions and the compositions reported in the literature share the same glass forming ability.It proves that this method is extensively applicable and could guide researchers in developing new glass formers with high GFA.Based on ternary clusters and entropy of mixing,the GFA,thermal stability and mechanical properties of Zr-Al-Fe-Cu BMGs were systemically investigated.It is found that this method is a good guide for designing glassy formers in complex ternary clusters system.Zr64.08Cu18.78Fe10.02Al7.12 and Zr60.32Cu22.56Fe9.95Al7.17 with highest GFA among those designed compositions were developed combining efficiently packed atomic clusters and mixing entropy.The corresponding cluster expressions are a7Fe(Fe3+Zr9)+?7Al(Zr8+Al2)+y7Cu(Cu4+Zr6)and a8Fe(Fe3+Zr9)+?8Al(Zr8+Al2)+-?8Cu(Cu5+Zr5),the coefficient ratios ?7/?7,?7/?7,?8/?8 and ?8/?8 are separately 0.948,1.499,0.961 and 1.511.To study the effects of minor alloying in ternary clusters system,Zr60.32Cu22.56Fe9.95Al7.17 was chosen as the basic composition,the effects of minor alloying of Nb on the GFA,thermal properties,mechanical properties and corrosion resistance in Zr-Al-Fe-Cu system were systemically investigated.It is indicated that minor alloying of Nb could decrease the thermal stability,increase the GFA and corrosion resistance in NaCl and HCl solution.Based on binary clusters and entropy of mixing,the GFA,thermal stability and mechanical peroperties of Zr-Al-Ni-Cu-Ag BMGs were systemically investigated.It is found that this mehod is a good guide for designing glassy formers in complex binary clusters system.Based on topological calculation of basic cluster and the assessment of similar element,the quantification of similar element replacement was solved.A series of fully glass with diameter up to 20 mm can be obtained in a narrow composition range of 49.24-50.12 at.%Zr,35.01-35.22 at.%Cu,2.69-2.79 at.%Ni,2.69-4.38 at.%Ag,and 8.58-9.28 at.%Al.The corresponding expressions are CBMG=aCu-Cu6.47-x Ni0.53AgxZr5+?Al-Al2Zr8(x=0.53-0.83).Except the GFA,the mechanical properties and thermal stability of these compositions were also superb.