Composition Design And Properties Of Zr-Based Bulk Metallic Glasses For Biomedical Applications Based On Dual-cluster Model

Zr-based bulk metal glasses(BMGs)exhibit a spectrum of excellent material properties such as high strength,high wear resistance,high corrosion resistance and good biocompatibility.Preparation of these desirable biomedical device materials,however,requires high purity contituent elements and high vacuum conditions.Zr-based BMGs with extremely large glass-forming ability(GFA),i.e.,with a critical diameter exceeding 10 mm,usually contain Ni or precious metal components.On the other hand,the largest compressive plasticity does not occur in the same composition range in which glass forms most easily in these systems.This has limited largely the massive production and processing of Zr-based BMGs.In the present work,we first summarize the single cluster model used for analyzing the known BMG alloy compositions.In view of the deficiency of the model,we use the eutectic principle and the atomic cluster plus glue atom model to propose a dual-cluster model for analysing BMG compostions and design Zr-based BMG compostions free of Ni and precious elements for sugical devices applications.The composition design starts from the ternary systems of Zr-Al-Cu and Zr-Al-Co,with which several multi-component systems have been obtained by alloying addition of a small amount of special other elments.Low-cost Zr-based BMGs have been prepared under low vaccum conditions,and the BMG alloys exhibit large GFA,high room-temperature plasticity,high wear resitstance,and corrosion resistance.Especially,cytotoxicity tests show that the BMG alloys possess superior biocompatibility to Ti-6A1-4V alloy.The surgical device applications of these new BMG alloys are promising in terms of the collection of favorable properties,such as high GFA,high strength and stiffness,high room-temperature plasticity,high wear and corrosion resistance,and the excellent biocompatibility.The significant experimental results obtained in the present work are presented in the following:Considering the deficiency of single cluster model for analysing multicomponent bulk metallic glass with large GFA,a dual-cluster model of BMGs is first constructed.By analysing the known BMG compositions(containing Ni or precious metals),the composition design scheme and procedures for Zr-based BMGs are proposed.A BMG alloy,namely,(Zr21Al3)(Cu7.5Fe1.5)=Zr63.5Al9Cu23Fe4.5,which is free of Ni and precious metal components,was derived from the eutectic composition Zr72.4Cu27.6 ≈[Cu-Zri4 + Zr-Cu4Zr9]Cu4 = Zr24Cu9.A critical glass-forming diameter of 10 mm can be reached at this composition by copper mold casting.By taking the composition Zr63 5Ak9Cu23Fe4.5 as the basis system,Zr6O.5Nb3Ak9Cy23Fe4.5,Zr60.5Hf3Al9Cu23Fe4.5 and Zr60.5Ti3Al9Cu23Fe4.5 BMGs with a centimeter scale critical diameter were successfully obtained with low purity raw materials and under a low vacuum level of 1 Pa.And the production cost was sharply reduced.The low-cost BMG alloys show excellent room temperature plasticity,wear resistance,corrosion resistance and biocompatibility.The room temperature compressive plasticity of Zr60.5Nb3Al9Cu23Fe4.5 BMG is about 5%.The wear mass loss of the BMG is by a factor of 1/2 smaller compared with that for Ti-6A1-4V alloy under the same wearing conditions.The corrosion current density in PBS of the BMG is two orders of magnitude lower than that of Ti-6A1-4V.The survival rate of CCD-986sk cells on the surface of the BMG(～63.2%)was significantly higher than that on Ti-6Al-4V(～46.6%).Further,a study for manufacturing hight specific strength BMGs has been cairried out in the Zr-Al-Co-Cu system.A series of ZrisAl6Co8-xCuxBMGs with high strength(>2.0 GPa)high stiffness(>90GPa)and high room temperature plasiticity(>3.5%)were obtained by using the dual-cluster model for biomedical devices applications.