Xu Zhuo, Tanaka Shingo, Kohyama Masanori
Department of Energy and Environment, Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology, 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, Japan.
J Phys Condens Matter. 2019 Mar 20;31(11):115001. doi: 10.1088/1361-648X/aafd00. Epub 2019 Jan 25.
We present ab initio calculations of grain-boundary (GB) segregation of the series of 3d transition-metal (TM) solutes in bcc Fe, taking advantage of the local-energy analysis. For [Formula: see text]11(3 3 2) and [Formula: see text]3(1 1 1) [Formula: see text] symmetrical tilt GBs, the segregation behaviors of 3d-TM solutes can be classified into three groups. The early TMs (Sc, Ti and V) are preferentially segregated to the looser sites of GBs antiferromagnetically, the late TMs (Co, Ni and Cu) are preferentially segregated to the tighter sites of GBs ferromagnetically, and the middle TMs (Cr and Mn) are segregated antiferromagnetically without fixed site preference. TMs at both ends of the 3d series show larger segregation-energy gains, while Mn shows a cusp at the center, which is similar to the ab initio interaction energies between the 3d-TM solutes and a screw-dislocation core in bcc Fe. By the local-energy analysis combined with the local densities of states, the segregation of the early TMs is mainly attributed to the stabilization of surrounding Fe atoms by the TM solute at the looser sites of GBs, and that of the late TMs is mainly attributed to the stabilization of the TM solute itself from bulk Fe to GB sites and the destabilization of Fe atoms around the TM solute in bulk Fe. The cusp at Mn is mainly caused by the destabilization of Fe atoms around the Mn solute in bulk Fe, due to nearly-localized high-spin d states of Mn, in contrast to substantial d-d hybridization for Mn in GBs. For each group of 3d-TM solutes, the effects on the magnetic and mechanical properties of Fe GBs are also analyzed by the d-electron behavior in common with the segregation mechanism.
我们利用局域能量分析，对体心立方铁中一系列3d过渡金属（TM）溶质的晶界（GB）偏析进行了从头算计算。对于[公式：见正文]11(3 3 2)和[公式：见正文]3(1 1 1)[公式：见正文]对称倾斜晶界，3d-TM溶质的偏析行为可分为三组。早期的TM（Sc、Ti和V）优先反铁磁性地偏析到晶界较疏松的位置，晚期的TM（Co、Ni和Cu）优先铁磁性地偏析到晶界较紧密的位置，而中间的TM（Cr和Mn）反铁磁性偏析且没有固定的位置偏好。3d系列两端的TM显示出更大的偏析能增益，而Mn在中心处出现一个尖峰，这与体心立方铁中3d-TM溶质与螺旋位错核心之间的从头算相互作用能相似。通过结合局域态密度的局域能量分析，早期TM的偏析主要归因于GB较疏松位置处的TM溶质使周围Fe原子稳定，而晚期TM的偏析主要归因于TM溶质本身从体相Fe到GB位置的稳定以及体相Fe中TM溶质周围Fe原子的失稳。Mn处的尖峰主要是由于体相Fe中Mn溶质周围Fe原子的失稳，这是由于Mn的近局域高自旋d态，与GB中Mn的大量d-d杂化形成对比。对于每组3d-TM溶质，还通过与偏析机制共有的d电子行为分析了它们对Fe晶界磁性能和力学性能的影响。
