Effects Of Ag Substitution For Fe On Properties Of Ni-free Zr-Cu-Al-Fe Bulk Metallic Glasses

Bulk metallic glasses?BMGs?have attracted much attention due to their unique physical and chemical properties.However,the critical size,poor plasticity at room temperature,and thermal stability of BMGs are considerable inferior,which has seriously limited the application prospect of the BMGs.To optimize various properties of BMGs,such as the GFA,mechanical properties,stability,and soft magnetic properties,micro-alloying is often an important solution.In this study,using Zr₆₀Cu₂₅Al₁₀Fe₅ as the basis,a new amorphous alloy system Zr₆₀Cu₂₅Al₁₀Fe_5-xAg_x?x=0,1,2,3,4,and 5 at%?was obtained by gradually replacing Fe with Ag.The effects of the substitution was examined by studying the GFA,crystallization kinetics,and mechanical properties using X-ray diffraction?XRD?,transmission electron microscopy?TEM?,differential scanning calorimetry?DSC?,uniaxial compression tests,and scanning electron microscope?SEM?.The microstructures of a series of as-cast alloy rods with different diameter were analyzed using XRD and TEM.The results showed that,under the same experimental conditions,the critical diameter for glass formation increased significantly by appropriately substituting Ag for Fe.The characteristic temperatures of each alloys,such as glass transition temperature?T_g?,onset temperature of crystallization?T_x?,melting temperature?T_p?,were obtained using differential scanning calorimetry?DSC?under different heating rate?5,10,20,30,and 40K/min?.Then the value of B,which could reflect the sensitivity of characteristic temperatures to the heating rate,and the activation energy,such as E_g,E_x,and E_p were calculated based on them.The result showed that the activation energies,including Eg,Ex and Ep,all increased significantly,which indicated that Ag addition reduced the sensitive of the amorphous alloys to temperature,and increased the energy barriers of atoms rearrangements,nucleation and growth,that is,the stability of the BMG enhanced enormously.The effect of replacing Fe with Ag on the mechanical properties of the alloy was studied by uniaxial compression tests under room temperature.The results showed that the room temperature plasticity was significantly improved:the plastic strain reached the maximum value?3.7%?at the Ag content of 4%,which was nearly ten times higher than the original component?0.4%?.In order to analyze the influence of Ag addition on the fracture behavior of the BMGs,the lateral surfaces and fracture morphologies of the samples after compressional tests were then performed using a SEM.