Fabrication,Mechanical Properties And Biocompatibility Of Zr-based Thin Film Metallic Glasses

Metallic glasses,as a newly-developed metastable material,have exhibited a series of outstanding properties,such as high strength/hardness,low elastic modulus,good wear resistance and biocompatibility.On the other hand,the poor room temperature ductility(<2%)and small product size stemming from the limited glass forming ability seriously limit the industrial application of bulk metallic glasses.With the development of thin film metallic glasses(TFMGs),there seems to be a way to solve this two problems at one time,giving rise to the possibility of TFMGs as a novel applied engineering metallic material.So far,the research on TFMGs is mainly focused on the fabrication and mechanical properties,less on the basic biological application.In our study,a Zr-based alloy system with a composition of Zr60.14Cu22.31Fe4.85Al9.7Ag3(at.%)have been fabricated by DC magnetron sputtering deposition using single alloy-target.X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),nanoindentation,friction/wear testing system,electrochemical workstation,cell cytotoxicity and proliferation have been employed to systematically investigate the microstructure,nano-hardness/Young's modulus,resistance of fretting and corrosion along with the biocompatibility of as-deposited TFMG.From the study of magnetron sputtering substrated temperature and bias voltage,we have found the substrate temperature show limited influence on the hardness and adhesion strength of TFMGs.Otherwise,increasing bias voltage would largely increase the adhesion strength of TFMGs.Optimizing sputtered TFMG has fully uniform single-phase amorphous structure,a high nano-hardness of ~7GPa and an ultra-high adhesion strength of 250 mN quantified by scratch test.Fretting tests against Si3N4 in air and artificial saliva solution both demonstrate that the as-deposited Zr-based TFMG has a lower wear rate of 4.48×10-4 mm3 N-1m-1 in air and 7.12×10-4 mm3 N-1m-1 in artificial saliva solution,about 2.8-times lower than that of Ti6Al4 V alloy.The oxidation wear mechanism was the dominating mechanism for Zr-based TFMG in fretting under two circumstances,which is actually reasonable as zirconium in TFMG is quite oxygen-affinitive.The dense Zr-rich oxide film formed along the worn trace can exhibit a good protection to the fretting damage.The corrosion properties of as-deposited TFMGs were evaluated by electrochemical measurements in artificial saliva solution at RT.The potendiodynamic tests show that the Zr-based TFMGs exhibit an excellent corrosion resistance with a pitting potential higher than 1V(vs.SCE)and a lower uniform corrosion rate than that of Ti6Al4 V alloy.The potentiostatic test further prove that the rate of formation of the passive film of Zr-TFMGs in the initial stage of immersion is faster and more stable than that of Ti6Al4 V alloy.Therefore,the rapid passivation and stability are the key reasons for the excellent corrosion resistance of Zr-TFMGs.The cytotoxicity test and immersion tests prove that the Zr-based TFMG is nontoxic to cells with a ultra-low ion release rate of Cu ion(1.17×10-3ug/cm2/5d),Al ion(4.05×10-3 ug/cm2/5d),within the safe range of human body.Cell adhesion,poliferation and mineralization tests indicate good bonding effect between Zr-TFMGs and cells.The number of cells increased steadily with the soaking time increasing.The cells show normal mineralization.All results demonstrate the good in vitro biocompatibility of the present Zr-based TFMG,similar to the well-known biocompatible Ti6Al4 V alloy.