Correlation Between Relaxation Behavior And Mechanical Properties Of Fe-based Amorphous Alloys

Amorphous alloys,also known as metallic glasses,combine the properties of metal and glass in performance.Due to the unique amorphous atomic arrangement structure,there are a certain amount of residual energy in amorphous alloys,which causes the constituent atoms of the amorphous alloy to be a relatively active state.The activity of internal atoms leads to the occurrence of relaxation process in amorphous alloys,which can be mainly divided into?relaxation and?relaxation.Their behavior is closely related to some basic characteristics of amorphous alloys.This thesis mainly studies the relaxation process of Fe-based amorphous alloy and its relationship with mechanical properties and includes the following two parts:?1?The previous research indicated that the substitution of Fe by Ni leaded to the great improvement of the plasticity of Fe₈₀P₁₃C₇ bulk metallic glass?BMG?.For example,20 at.%of Fe replaced by Ni in Fe₈₀P₁₃C₇ BMG results in the increase of the room temperature compressive plastic strain from 1%to 16%.In this work,a comparative study on relaxation behaviors between Fe₈₀P₁₃C₇ and Fe₆₀Ni₂₀P₁₃C₇BMGs have been studied in order to investigate the origin of the extraordinary plasticity caused by the substitution of Ni for Fe in Fe-Ni-P-C BMGs.There is only have?-relaxation as excess wings in the dynamic mechanics spectrum of Fe₈₀P₁₃C₇BMG,while Fe₆₀Ni₂₀P₁₃C₇ BMG exhibits?-relaxation as a hump with a quite low activation energy of about 62 kJ/mol.This work has evidenced that the?-relaxation behavior has close correlation with the plasticity in Fe-Ni-P-C BMGs,and this founding is believed to have implications for understanding the origin of plasticity from the perspective of?-relaxation in BMGs.?2?In the second work,we studied the effect of the preparation cooling rate on relaxation processes of Fe-based amorphous alloys.The Fe₈₀P₁₃C₇ BMG and melt-spun ribbon are prepared by J-Quenching technology and melt-spinning technology,respectively.The results of synchrotron radiation analysis show that,compared with melt-spun ribbon,the Fe₈₀P₁₃C₇ BMG prepared at a lower cooling rate has a higher short-range order and higher packing density.The atomic cluster connectivity inside the sample is also better.The results of dynamic mechanical test analysis show that the loss modulus of Fe₈₀P₁₃C₇ BMG is lower than that of melt-spun ribbon,indicating the fewer number of liquid-like regions associated with relaxation events,which is consistent with the results of synchrotron radiation analysis.The results of the work show that the difference in atomic arrangement of amorphous alloys affects its relaxation behavior.