Study For Size Effect And Phase Stability Of Nano-Binary Alloy

Nowadays nanoparticles have become very popular due to their special properties. Properties of nano-material depend on the size of its component units, and thus size effect of nano-material as the key to the properties design. Taking account of effect of the surface and size, the thermal stability and amorphization process of some typical nano based binary alloys, including the formation enthalpy and the critical sizes of crystallization and amorphization, calculated by means of subregular model in this paper.Simulating the thermal stability of nano Ti based binary alloys with different particle size, it shows that the smaller the particle size, the greater the enthalpy of formation and the worse the stability of the structure. Also, the results show that the component segregation for the nano Ti based binary alloys is very clear when the grain size is less than 10 nm. The aggregation element and the degree of aggregation are controlled by the surface energy and aggregation drive energy. Components segregation also has a great impact for the structural stability of the nano-alloy.Simulating the non-crystallization process of nano Au-Sn and In-Sn alloy particles, the results reveal that the thermal stability of nanoparticle decreases and the crystalline phase may be driven into an amorphous phase with reducing particle size. More importantly, the model reveals the phenomena of amorphization process such as a continuous crystalline-to-amorphous transition and the amorphization ability reinforcement and the glass forming range (GFR) broaden with decreasing the size of nanoparticle. It is shown that surface effect and size effect have important roles in crystalline-to-amorphous transition. At the same time, the Au-35 at.% Sn and In-70 at.% Sn particles are pure amorphous when their sizes are smaller than 12 nm. The predictions of the critical diameter from our model are consistent with the experimental results.In previous studies, the traditional theories did not analyze the alloy formation and the phase transition of immiscible metal system because its formation enthalpy is positive. In this paper, we study the phase stability of Bi-Sn and Fe-W immiscible metal systems with subregular model. The results show that the structure of Bi-Sn alloy is pure amorphous phase when its particle size is smaller than 11nm, and its composition does not affect the glass transition; while for Fe-W nanoparticle, the effect of composition is obvious and the GFR broaden with decreasing the size of nanoparticle, when the composition of W is larger, the critical size for non-crystallization is smaller.