Exploration Effects Of Annealing Combined High Rheological Forming On Mechanical Properties Of Zr-based Bulk Metallic Glasses

Due to their excellent mechanical properties,metallic glass has attracted great attention.But its poor plasticity has limited their pratical application.In addition,the metallic glass is in energy metastable state,under certain conditions will transfer to low-energy state even the crystalline state,which is called structural relaxation.Furthermore,the mechanical properties of relaxed metallic glass are often deteriorated.The high rheological forming?HRRF?of the innovation development by our research group has been demonstrated in previous experiments to remarkably improve the room temperature compressive plasticity of a brittlement bulk metallic glasses?BMGs?with composition Z_r48Cu₃₆Al₈Ag₈.However,the law of mechanical properties,thermal stability and mechanism of the method for the relaxed BMGs remains to be seen.In this paper,we took two Zr-based bulk metallic glasses?BMGs?with composition Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀ and Zr₅₇Cu₂₀Ni₈Al₁₀Ag₅ as research objects.Based on the possibility of improving plasticity of ZrCuAlNi-based BMGs after HRRF,we studied the effect of HRRF on mechanical properties of relaxed Zr₅₇Cu₂₀Ni₈Al₁₀Ag₅ BMGs.The microhardness,compressive test and bending test were conducted to measure the variations of mechanical properties.Scanning electron microscope?SEM?and transmission electron microscope?TEM?were adopted to unveil the changes of microstructure.Differential scanning calorimetry?DSC?was conducted to measure impact of HRRF on stablility of relaxed BMGs.The main research results and conclusions are as follows:1.For HRRF treatment of Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀ BMG,DSC result shows the free volume content is higher than as-cast.The compressive plasticity and bending plasticity improved from 16.76%and 3.04%of as-cast to>50%and>6.11%without fracture,respectively.SEM result show the shear bands of as-cast processed by HRRF produces a large number of branches,showing multiple shear bands.TEM result shows the precipitation of I-phase in amorphous matrix..2.The microhardness of Zr₅₇Cu₂₀Ni₈Al₁₀Ag₅ BMGs upon annealing at temperature below its glass transition temperarute,T_g,increases with annealing time.After HRRF treatment of annealed sample,the microhardness was recovered to the as-cast level.The compressive plasticity of isothermal annealed samples increase with annealing time up to 3h and decrease as annealing time extends,the compressive plasticity of isothermal annealed 3h sample was 31.19%,three-point bend test shows the bending plasticity increases from 0.81%of as-cast to 2.0%.after HRRF.The plasticity of annealed samples processed by HRRF has drastically improved except the isothermal annealed 1.5 h sample plastic increase to 9.84%,the plasticity of rest annealed sample are>40%.3.SEM images show after HRRF treatment of isothermal annealed samples,the shear bands apparently appear bifurcation,indicates HRRF treatment can change the formation and evolution of shear bands.TEM results show that phase separation appears in annealed samples and the size of HRRF processed annealed samples separation phase further increase.DSC results show that annealing induced free volume annihilation and after HRRF processed annealed samples,the free volume content increase.The enhancement of plasticity of annealed samples and annealed samples processed by HRRF were due to phase separarion and free volume coupling effect.4.In terms of the metal-glass structuring relationship,the phase separation and quasi-crystal phase produced by annealing and HRRF treatment significantly promoted the plasticity of BMGs.However,as for the difference of scale and composition fluctuation,they are in different microstructure.Although at present is still uncertain,phase separation and quasi crystal phase in other a morphous department whether can use annealing or HRRF method,but this article research results provide important basis for plasticizing of BMGs from microstructure and broaded the plasticizing thoughts.