本研究以分子動力學研究鎳鈦合金塊材之形狀記憶特性，觀察不同升降溫速率、不同模型尺寸、不同鎳含量比例與不同原子分佈的情況下對相轉變的影響。也探討鎳鈦合金塊材之擬彈性效應，在沃斯田體相下對完美模型、隨機點缺陷模型與中心球型缺陷模型進行循環加載模擬，使用W參數法分析加載過程中有無生成差排情況下對於相轉變的影響，並比較不同形式與比例之缺陷模型的相變與差排行為。
在升降溫模擬結果得知，鎳鈦合金在高溫時以體心立方結構(沃斯田體相)穩定存在，在低溫時則相變為斜方體結構(麻田散體相)，且相變溫度會隨著鎳含量增加而降低。此外，對於鎳含量為51%的鎳鈦合金而言，相轉變溫度不受其內部原子分佈位置影響，且在常溫300K下結構處於沃斯田體相，並以此狀態下進行循環加載模擬。
在循環加載模擬結果得知，若加載中無差排情況下則會使結構處於更穩定的狀態，相變提前發生現象；若加載至差排情況下會使相變更難發生，相變應力提升現象。在比較缺陷模型之模擬結果得知，相變應力與差排應力皆會隨著缺陷比例增加而下降，且點缺陷對於相變造成的影響比球型缺陷大。本研究提供一套循環加載模擬的流程與方法，並在不同模型與不同加載情況下，得到彼此間與擬彈性效應的關係，作為往後研究鎳鈦記憶合金之擬彈性行為之參考。

The shape memory properties of NiTi alloy bulks were investigated using molecular dynamics simulation. First, the phase transformation behaviors for various Ni composition ratios were studied under cooling and heating process. Different defect of models applied cyclic loading and the atomic configurations were inspected and further analyzed using both W parameter and slip vector. For the simulations, it was found that 51%NiTi is body-centered cubic structure (austenite) at high temperature and transforms to martensite phase at specific temperature. It was observed that the phase transformation temperature was affected by different Ni composition ratio, but the different atomic arrangement would have the same phase transformation temperature. For the defect of models under cyclic loading, it was found that the models have been more stable and the stress for stress-induced martensitic transformation has been found to decrease with the number of cycles. However, the models occurred dislocations during the loading process which would inhibit the phase transformation. We also observed the stress concentration effect that lead to the transformation stress decreased. Our results provide an atomic basis for further study of pseudoelastic effect on NiTi alloy bulks under cyclic loading.

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