Role of grain boundary character on oxygen and hydrogen segregation-induced embrittlement in polycrystalline Ni
Role of grain boundary character on oxygen and hydrogen segregation-induced embrittlement in polycrystalline Ni
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DOI：
10.1007/s10853-016-0389-3
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发表时间：
2017-01-01
影响因子：
4.5
通讯作者：
Dongare, Avinash M.
中科院分区：
文献类型：
--
作者：
Chen, Jie;Dongare, Avinash M.
通过密度泛函理论 (DFT) 计算来研究晶界对多晶镍系统中氧和氢偏析引起的脆化相关能量的作用。选择镍的四个模型晶界 (GB) 系统来研究这种效应。这些模型GB是I 5磅（012）GB、I 5磅（013）GB、I 11磅（113）GB和I 3磅（111）相干孪晶边界（CTB）。与其他 GB 相比，所选 GB 能够研究 CTB 在脆化和脱聚机制中的作用。这里考虑的脆化机制是基于对以下能量学的研究：(a) GB 处脆化物质（氧、氢）的原子偏析； (b) 由于脆化物质在 GB 处的偏析而形成空位； (c) 与 GB 处的脱聚有关的能量学，作为 GB 处脆性物质的浓度/积累的函数。 DFT 计算表明，脆化物质的偏析和脆化效应与晶界的局部原子结构和相关的过剩自由体积密切相关。特别地，发现基于脆化物质的结合能，I 3 磅(111) CTB不太容易发生氧和氢的分离。然而，在所有考虑的 GB 中，发现 I 3 磅 (111) CTB 在存在少量偏析氧原子的情况下最容易受到 GB 脱聚和裂纹形成的影响。 I 3 磅 (111) CTB 的这种双重行为也通过 DFT 模拟在氢作为脆化物质的情况下得到了证实。因此，观察到抗偏析的I 3 磅(111) CTB在存在少量偏析的脆化原子的情况下最容易形成裂纹。讨论了脆化物质偏析的能量学以及偏析对空位形成能和晶界脱聚的影响。
Density functional theory (DFT) calculations are carried out to investigate the role of grain boundaries on the energetics related to the oxygen and hydrogen segregation-induced embrittlement in polycrystalline Ni systems. Four model grain boundary (GB) systems for nickel are chosen to investigate this effect. These model GBs are the I 5 pound (012) GB, the I 5 pound (013) GB, the I 11 pound (113) GB, and the I 3 pound (111) coherent twin boundary (CTB). The chosen GBs enable the investigation of the role of the CTB in the embrittlement and decohesion mechanisms in comparison with the other GBs. The embrittling mechanism considered here is based on the investigation of the energetics related to (a) the segregation of atoms of embrittling species (oxygen, hydrogen) at the GB; (b) the formation of vacancies due to the segregation of embrittling species at the GB; and (c) the energetics related to decohesion at the GB as a function of concentration/accumulation of the embrittling species at the GB. DFT calculations suggest that the segregation of the embrittling species and the embrittling effect are closely related to the local atomic structure of the GB and the associated excess free volume. In particular, it is found that the I 3 pound (111) CTB is less prone to segregation of oxygen and hydrogen based on the binding energetics of the embrittling species. However, among all the GBs considered, the I 3 pound (111) CTB is found to be most susceptible to GB decohesion and crack formation in the presence of small amounts of segregated oxygen atoms. This dual behavior of the I 3 pound (111) CTB is also confirmed for the case of hydrogen as the embrittling species using DFT simulations. Thus, the segregation-resistant I 3 pound (111) CTB is observed to be the most susceptible to crack formation in the presence of small amounts of segregated embrittling atoms. The energetics of segregation of the embrittling species and the effect of segregation on the vacancy formation energies and GB decohesion are discussed.