Structure Stability Of A Cu-based Bulk Metallic Glass During The High Temperature Super-plastic Deformation

The Cu-based bulk metallic glasses (BMGs) have a potential for practical applications owing to their glass-forming ability (GFA),high strength and relatively low-priced.Research on the microstructure evolution and the influence of super plasticity on the properties of BMGs at room temperature have a significance for the structure controlling of the BMGs.In this work,the rod of the studied Cu-based BMG a diameter of 2 mm and 3 mm were prepared by water-cooled copper mould sucking method.The compressive deformation behavior of the alloy under different temperatures and strain rates was investigated.The deformation mechanisms in the SLR and the influence of super plasticity on the crystallization behavior was discussed.Meanwhile,isothermal annealing treatment of the post-deformed simple was investigated,and the effects of super-plasticity deformation on isothermal crystallization behavior and the mechanical properties of BMGs were discussed.The conclusion as followed:(1) The deformation of (Cu₅0Zr₅₀)₉₂Al₈ BMGs is strongly dependent on strain rates and temperatures.The BMG exhibits nearly Newtonian behavior below the strain rate of 2.5×10^-3 s^-1 at 750 K,but become non-Newtonian at the high strain rates and at low temperatures.Based on the true stress-strain curves under the different temperatures and strain rates,an empirical deformation map could be constructed to provide the boundary between the Newtonian and non-Newtonian ?ow regimes.(2) The non-Newtonian plastic deformation in the super-cooled liquid region had a significant effect on crystallization behavior,thermal stability and the mechanical properties.The results showed that non-Newtonian plastic deformation promoted the formation of nano-crystalline in the amorphous matrix at the relatively low temperature (740 K),and the formation of nano-crystalline also reduced fracture stress of (Cu₅0Zr₅₀)₉₂Al₈ BMG at room temperature;When the temperature at 750 K,the deformation reduces the thermal stability of the alloy, and the partially crystallization occurs during the deformation in the alloy. The extent of the crystallization is strongly dependent on the deformation strain, and as the strain increases to 80%, the peaks of the crystallites can be clearly observed on the XRD pattern of the alloy. The present of the crystallites promotes the micro-hardness of the alloy.However,the Newtonian plastic deformation in the super-cooled liquid region had no effect on crystallization behavior.(3) After vacuum annealing on the simple non-Newtonian deformed (730 K,ε& =5×10^-3s^-1),mixed CuZr parent phase (B2 phase,Pm3m) and monoclinic martensite (P21/m and Cm space group) formed.The simple exhibits super-elasticity at room temperature.As the strain is 8%,the maximum recovered strain of the simple annealed is 5%.