The Research On Forming Ability And Crystallization Behavior Of CuZrAlNb Alloys

The effect of the added elements Zr and Cu on glassy forming ability and mechanical properties and the effect of different sizes of alloys were systematically studied in the Cu50-xZr40+xAl5Nb5(x=0,2,4,6) alloys in this paper. Moreover, the analysis by differential scanning calorimetry of BMG was investigated.The alloys rods that atom percentage is Cu50-xZr4o+xAl5Nb5(x=0,2,4,6) were prepared by using magnetic-suspending melting alloy ingots and copper-mold casting. The best glass former Cu46Zr44Al5Nb5were full amorphous structure with diameters of3.0mm, while the other alloys were amorphous composite constituted by the crystalline phase and amorphous phase. Cu46Zr44Al5Nb5BMG had an undercooled liquid region (⊿T=TX-Tg, where Tg is the glass transition temperature and Tx is defined as the onset temperature of the first crystallization event) of52K, reduced glass transition temperature Trg (Trg=Tg/Tl, where Tl is the liquidus temperature) of0.60, and γ was0.401.Mechanical properties of amorphous composite Cu44Zr46Al5Nb5with fracture strength of1747MPa and plastic strain of3.94%was better than amorphous composite Cu48Zr42Al5Nb5. This result was due to the difference of sizes, distribution, volume fraction of the crystalline phase.The analysis of DSC curves, X-ray diffraction(XRD) patterns and electron diffraction taken from the rods of Cu46Zr44Al5Nb5with different diameters(3mm,4mm,6mm), indicates that the critical casting thickness is up to6mm at lest. Tg values are higher for the Cu46ZrAl5Nb5amorphous alloy rod with diameters of3.0mm than for the rod with diameters of4.0mm and6.0mm. Moreover, it is obviously that the crystallization enthalpy which reduces from54.82J/g to51.61J/g as the increase of the diameters from3.0to6.0mm for these amorphous alloy rods is different from each other. This phenomenon exhibits that the tendency of crystallization becomes greater as the decrease of the cooling rate resulting from the increase of the diameters.The fracture strength are1811MPa,1669MPa,1501MPa, respectively, for with diameters of3.0,4.0and6.0mm. It is noticed that fracture strength for Cu46ZrAl5Nb5amorphous alloy rods increase while the diameter changes from3to6mm corresponding to the result that Tg values. It is well known that Tg reflects the binding force among the constituent elements.It is calculated that the glass transition activation energy (Eg), the activation crystallization energy(Ex), and the activation crystallization apex energy (Ep), respectively, are231.96KJ/mol,351.39KJ/mol,401.36KJ/mol by non-isothermal crystallization analysis of Cu46Zr44Al5Nb5BMG. When the velocity of ascending temperature quicken, Tg, Tx, Tp will excursion to the field of high temperature and the three sample show the obvious kinetics Mechanical property.