Research On The Glass Forming Ability And Performance Of Nd-based Bulk Metallic Glass

Since the first Nd-based bulk metallic glass (BMG) composition with large glass forming ability (GFA) in Nd-Fe-Al ternary system was found by A.Inoue in 1996, intensive attention had been paid to Nd-based BMGs due to their good mechanical performance and excel-lent magnetic property. Up to now, however, it’s still lack of understanding and description of the GFA of Nd-based BMGs from the aspect of microstructure as earlier researchers ex-plained its excellent GFA based on thermodynamics principle.In this dissertation, clusters were used to understand and decipher Nd-based BMGs with large GFA from the aspect of microstructure. Different clusters were explored in Nd-M (M=Fe, Ni, Co, Cu, Zn and Al) basic binary systems. Nd-Ni binary clusters were finally cho-sen by comparing clusters and corresponding eutectic points in binary phase diagram with the model of cluster-plus-glue-atom.According to cluster-plus-glue-atom model, three Nd-riched eutectic points Nd81Nii9, Nd73Ni27 and Nd65Ni35 could be regarded as [Ni-Nd9](Ni)1, [Ni-Ni2Nd7](Nd)1 and [Ni-Ni2Nd7](Ni)1, separately. Compositions with large GFA in quaternary and quintuple Nd-based BMGs were finally deciphered by the way of changing the glue-atom and similar elements replacement. Quaternary Nd-based BMG composition Nd63.64Cu18.18Ni9.09Al9.09 could be regarded as [Ni-Cu2Nd7](A1)1 with the model of cluster-plus-glue-atom, its critical diameter is 4mm by copper mould casting. Quintuple Nd-based BMG composition Nd50La13.64Cu18.18Ni9.09Al9.09 could be regarded as [Ni-Cu2Nd5.5La1.5](A1)1 with the model of cluster-plus-glue-atom, its critical diameter is 5mm by copper-moud casting.GFA in Nd-based BMGs increased along with similar elements Cu and La replacing Ni and Nd in cluster’s shell. From the view of inner structure, the replacement by similar ele-ments enhancing GFA is caused by the higher topological close-packing.Form the aspect of mixing entropy and entropy of mixing, the replacement of Ni atoms in cluster’s shell by 2Cu atoms enhancing GFA greatly is caused by mixing entropy in Nd-based systems increasing form -31.8 kJ/mol to -25.3kJ/mol, margining at 20.4 percent, along with an increase of 16% of entropy of mixing in systems. Form the view of mix-ing entropy and entropy of mixing, the replacement of 1.5Nd atoms in cluster’s shell by 1.5La atoms enhancing GFA greatly is caused by entropy of mixing in Nd-based systems in-creasing in systems.