Effect Of Replacement Of Similar Metal Elements On Mechanical Properties Of Transition Metal-based Amorphous Alloys

In this thesis,the first-principles molecular dynamics simulation method was used to study the effects of similar metal elements?Fe,Ni,Co?substitution on the mechanical properties of transition metal-based amorphous alloys,including two tasks:?1?In the first work,we calculated the atomic arrangement of three metallic glasses?MGs?of Fe₈₀P₁₄B₆,Fe₄₀Ni₄₀P₁₄B₆ and Ni₈₀P₁₄B₆ using first-principles molecular dynamics simulation,and studying the effect of mutual substitution of Fe and Ni on the plasticity of Fe-Ni-P-B MGs from the perspective of atomic arrangement.The results reveal that Fe₄₀Ni₄₀P₁₄B₆MG has more vertex sharing clusters and less edge-sharing clusters compared to Fe₈₀P₁₄B₆ and Ni₈₀P₁₄B₆ MGs,indicating that Fe₄₀Ni₄₀P₁₄B₆ MG possesses more cavities or boundaries on medium-range order?MRO?,which are beneficial for plastic deformation.In addition,large clusters have relatively strong connection with comparatively smaller clusters in Fe₈₀P₁₄B₆ and Ni₈₀P₁₄B₆ MGs while the clusters with the similar size tend to form the nearest neighbor in Fe₄₀Ni₄₀P₁₄B₆ MG.Compared with the former,the connection mode of the latter may form relatively loose packing,which can facilitate plastic deformation.Fe₄₀Ni₄₀P₁₄B₆MG has larger population of 142x,1441 and 1661 bond pairs,which are crystal-like clusters,and relatively smaller 1551and 1541.Besides,Fe₄₀Ni₄₀P₁₄B₆MG has less<0 0 12 0>,<0 110 2>and<0 2 10 1>clusters and more<0 4 4 3>and<0 4 4 6>compared to Fe₈₀P₁₄B₆and Ni₈₀P₁₄B₆MGs,indicating the replacement of Fe by Ni or Ni by Fe in Fe/Ni-based MGs reducesfive-fold rotational symmetry and the formation of nanocrystal.These changes in microstructure contribute to plastic deformation.?2?In the second work,the three MGs of Fe₈₀P₁₄B₆,Fe₄₀Co₄₀P₁₄B₆ and Co₈₀P₁₄B₆were selected to study and the relationship between the atomic arrangement structure and mechanical properties in these MGs was analyzed from the perspective of the short-range order?SRO?and medium-range order?MRO?.Through the analysis of thepair distribution functions,Voronoi polyhedron,coordination number,bond pair,pentagon and other short programs,it is found that the mutual substitution of Fe and Co elements leads to reduction of the fivefold symmetry and the increase of free volume,which may be beneficial for plasticity.It can be found from the cluster connection mode and the correlation index between clusters that,compared with Fe₈₀P₁₄B₆ and Co₈₀P₁₄B₆MGs,Fe₄₀Co₄₀P₁₄B₆ MG has more vertex-sharing clusters and less edge-sharing clusters,indicating that Fe₄₀Co₄₀P₁₄B₆ MG possesses more cavities or boundaries?two major defects in the amorphous process?on MRO,which lead to a relatively loose packing.The motion of the atomic cluster under the load is coordinated by the defect,which leads to the shear transition event.As the load increases,the defective area in the MRO undergoes relatively large plastic deformation.Therefore,we speculate that the difference in the plasticity of the three MGs may be attributed to the difference in the amount of the holes or boundaries on the MRO,which are related to the connection between the clusters.In addition,larger clusters have a more strong connection with relatively smaller clusters in Fe₈₀P₁₄B₆and Co₈₀P₁₄B₆ MGs while the clusters with the similar size tend to form the nearest neighbor in Fe₄₀Co₄₀P₁₄B₆ MG.Compared with the former,the connection mode of the latter may form relatively loose packing,which is beneficial for forming shear band under the load and is favorable for the proliferation of the shear band.