Effects Of Melt Temperatures On Relaxation Behavior And Mechanical Properties Of Bulk Metallic Glasses

Metallic glasses?MGs?are produced by rapid quenching from the melt.Therefore,the structure of melt could be retained to BMGs at most extent.The atomic structure of MGs is amorphous.MGs are thermodynamically out-of-equilibrium and could change from the high-energy state to the low-energy state under a certain conditions,which is called “structure relaxation”.Studying the relaxation of MGs is beneficial to understand the nature and mechanical properties of MGs.It is very meaningful to study the relaxation behavior and mechanical properties by using the entry point of the melt of MGs.In this background,Zr₅₇Cu₂₀Al₁₀Ni₈Ag₅ and La₆₂Al₁₄(Cu_5/6Ag_1/6)₁₄(Ni_1/2Co_1/2)₁₀ bulk metallic glasses?BMGs?were manufactured using the copper-mould injecting method by altering the melt temperature.Differential scanning calorimeter?DSC?,internal friction,electrical resistance,Dynamic mechanical analysis?DMA?,mechanical property test and scanning electron microscope were adopted to study effects of melt temperatures of relaxation behavior and mechanical properties,the relaxation behavior and the relationship of the relaxation behavior and mechanical properties of BMGs.The superficial points and main results of this paper are listed below:1.The effects of melt temperatures of Zr₅₇Cu₂₀Al₁₀Ni₈Ag₅ BMGs on relaxation behavior were studied by the internal friction and electrical resistance.With increasing the melt temperature,the supercooled liquid region of BMGs is enlarged and Tx shifts to the higher temperature,indicating that the thermal stability of BMGs is enhanced.The internal friction of BMGs at low temperature is increased with elevating the melt temperature,showing the free volume is increased.Besides,the ?-relaxation is explored by electrical resistivity measurement innovatively.The variation of electrical resistance due to the ?-relaxation before Tg represents the intensity of the ?-relaxation.With elevating the melt temperature,the ?-relaxation behaves more evident.2.The effects of melt temperatures on the structure relaxation of La₆₂Al₁₄(Cu_5/6Ag_1/6)₁₄(Ni_1/2Co_1/2)₁₀ BMGs was studied using DSC and DMA.The results of DSC shows that increasing the melt temperature leading to the enlargement of the supercooled liquid region and the shift to the higher temperature of Tx of BMGs,improves the thermal stability and GFA.And the results of DMA reveal that with elevating the melt temperature,the storage modulus increases with elevating the melt temperature and the ?-relaxation becomes more evident.And according to the fitting of the Arrhenius equation,activation energies of ?-relaxation and ?-relaxation decrease with the increase of the melt temperature.The degree of coupling between the two relaxation modes is also weakened,showing the ?-relaxation separates from the ?-relaxation gradually with elevating the melt temperature.It is worth mentioning that the specific value of the empirical law?E?/RTg=26?decreases with the increase of melt temperature,which could be related to the free volume.3.The effects of melt temperatures of Zr₅₇Cu₂₀Al₁₀Ni₈Ag₅ and La₆₂Al₁₄(Cu_5/6Ag_1/6)₁₄(Ni_1/2Co_1/2)₁₀ BMGs on mechanical properties were studied by compressive test,micro-hardness test and SEM.The compressive plasticity of both BMGs improves with increasing the melt temperature.It shows that the more pronounced ?-relaxation,the better mechanical properties of the BMGs,indicating that the mechanical properties have a close relationship with the ?-relaxation.And the results of micro-hardness test show that with increasing the melt temperature,the heterogeneity of micro-hardness is more obvious,and the distribution of the hard region and the soft region within the scope of micro-hardness becomes more homogeneous.Moreover,the section morphology of Zr₅₇Cu₂₀Al₁₀Ni₈Ag₅ BMGs was observed by SEM,showing that with the increase of the melt temperature,the number of shear bands is increased and the interaction between them are enhanced.And the vein pattern of BMGs also increases with elevating melt temperatures.