本研究之重點在於探討不同鎳鋁比例之鎳鋁合金奈米板，在不同淬火速率下之機械性質，以及觀察裂縫之傳播如何影響其破壞行為。模擬所使用之方法為分子動力學模擬法，並選用EAM勢能函數，搭配軟體LAMMPS作為模擬工具，分析各個材料在不同淬火速率下之結晶分佈，並在淬火後之模型上預設裂縫，經由單軸拉伸觀察裂縫之傳播行為，並探討裂縫數量、裂縫大小及淬火速率對材料之機械性質的影響。模擬結果顯示，五種材料中，Ni25Al75具有最佳之非晶形成能力，Ni50Al50則最不易形成非晶。而從淬火速率為0.5K/ps之模型中，可同時觀察到兩種截然不同的破壞方式，分別是屬於脆性破壞的Ni40Al60和Ni50Al50及屬於韌性破壞的Ni25Al75和Ni75Al25。就裂縫之效應來看，當裂縫數量增加，材料之極限應力值隨之下降，而改變裂縫大小時，裂縫長度之變化造成的影響會大於裂縫寬度。隨著淬火速率提升，各材料之非晶比例會隨之上升，但極限應力值則隨之下降。而在淬火速率為25K/ps之下，所有材料幾乎完全為非晶結構，此時模型之破壞均是透過剪切帶之傳遞，且極限應力值之大小也與模型內鎳原子比例成正比。

In this thesis, the program package LAMMPS with EAM potential is adopted for performing molecular dynamics simulations to investigate the mechanical and fracture behaviors of NiAl alloy with five different ratios of Ni and Al. At first, the distributions of different types of crystallization within each material under five different quenching rates are evaluated, and they are used as simulation models subjected to uniaxial tension. Besides, a crack is imposed on physical models prior to simulation. The effects of cracks on the fracture of materials are then investigated. It is found that among five different materials, Ni25Al75 has the best amorphous formation ability, while Ni50Al50 has the worst. There exist two distinct fracture behaviors at quenching rate 0.5K/ps, i.e., brittle fracture for Ni40Al60 and Ni50Al50 while ductile fracture for Ni25Al75 and Ni75Al25.The magnitude of the ultimate stress is decreased with the increase of crack number. Moreover, the effect of crack length on the mechanical properties and fracture mechanism is more significant than the crack width. Moreover, it is found that the magnitude of the ultimate stress of materials is decreased as the quenching rate is enhanced. As the quenching rate reaches 25K/ps, microstructure of all the materials is almost amorphous, leading to the deformation and fracture mechanisms through the propagation of the shear band. Meanwhile, the magnitude of the ultimate stress is increased with the increasing contents of Ni in NiAl alloy.

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