Ductile to brittle transition (DBT) phenomenon is commonly observed in BCC Fe-based systems, which significantly deteriorates their low temperature fracture toughness. Ni is known to be an effective alloying element to improve the low temperature toughness by reducing the ductile to brittle transition temperature (). The present article investigates the role of Ni in tailoring the DBT curve of BCC Fe by employing molecular dynamics (MD) simulation. Here, we performed mode-I loading of different pre-cracked systems (pure Fe, Fe-2 wt% Ni and Fe-4 wt% Ni alloys) over a temperature range of 1–800 K to construct their DBT curves. The DBT curves are subsequently correlated with the temperature sensitivity of fracture stress, which is estimated using the concept of critical strain energy release rate (). The role of Ni in reducing the fracture stress sensitivity is responsible for decreasing the as well as the slope of the DBT region. The underlying mechanism is discussed in terms of the crack blunting effect of Ni which effectively increases the and hence the fracture stress, particularly at the low temperature regimes. Besides, the significantly large strain rate imposed in MD simulation is mainly responsible for the higher values when compared with the experimental results. The present paper tackles this strain rate issue by using an appropriate strain rate sensitivity factor to rescale the simulated values down to the experimental ones, resulting in a good match between the simulated and experimental .

中文翻译：

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使用分子动力学模拟研究二元 Fe-Ni 系统中的延性到脆性转变现象

在 BCC 铁基体系中经常观察到延性转变（DBT）现象，这显着降低了其低温断裂韧性。众所周知，Ni 是一种有效的合金元素，可以通过降低延性到脆性的转变温度来提高低温韧性。本文采用分子动力学 (MD) 模拟研究了 Ni 在调整 BCC Fe 的 DBT 曲线中的作用。在这里，我们在 1–800 K 的温度范围内对不同的预裂系统（纯 Fe、Fe-2 wt% Ni 和 Fe-4 wt% Ni 合金）进行 I 型加载，以构建其 DBT 曲线。 DBT 曲线随后与断裂应力的温度敏感性相关，断裂应力是使用临界应变能释放率的概念来估计的 ()。 Ni 在降低断裂应力敏感性方面的作用是降低 DBT 区域的斜率的原因。根据镍的裂纹钝化效应讨论了潜在的机制，镍有效地增加了裂纹应力，从而增加了断裂应力，特别是在低温状态下。此外，与实验结果相比，MD 模拟中施加的显着较大的应变率是导致该值较高的主要原因。本文通过使用适当的应变率敏感因子将模拟值重新调整为实验值来解决这个应变率问题，从而使模拟值与实验值之间具有良好的匹配性。