Energy landscape of deformation twinning in bcc and fcc metals
Energy landscape of deformation twinning in bcc and fcc metals
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DOI：
10.1103/physrevb.71.224102
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发表时间：
2005-06-01
影响因子：
3.7
通讯作者：
Yip, S
中科院分区：
文献类型：
--
作者：
Ogata, S;Li, J;Yip, S
用密度泛函理论计算了bcc结构Mo中（2（1）over bar（1）over bar）< 111 >形变孪晶和fcc结构Al和Cu中（111）< 11（2）over bar >形变孪晶的能量分布，并计算了层间滑移的能量分布。在体心立方钼中，亚稳孪晶的最小厚度为两层，而三层和四层的孪晶胚胎是不稳定的。从五层开始，Mo孪晶可以逐层生长。孪晶界的形成能和迁移能分别为607和40 mJ/m，这意味着孪晶界上的部分位错将具有宽核和高迁移率。在厚孪晶的边界上均匀成核部分环的应力被确定为仅1.4 GPa，这表明一旦Mo中的变形孪晶达到临界厚度，我们估计为六层，它可以相当容易地生长。基于简单的缺陷力学考虑，我们估计失控缺陷生长的条件要求孪晶胚厚度为数十层。比较Mo与Al和Cu的孪晶能谱，发现Mo具有更大范围的层间机械耦合，这是由于层间成角键和较弱的电子屏蔽所致。Al和Cu之间的相互作用范围相对较长。
Energy landscapes of (2 (1) over bar(1) over bar)< 111 > deformation twinning in bcc Mo and (111)< 11 (2) over bar > deformation twinning in fcc Al and Cu are determined using density functional theory for sliding of layers numbering up to 7. In bcc Mo, the minimum thickness of a metastable twin is two layers, while twin embryos of three and four layers are unstable. Starting from five layers, the Mo twin can grow in a layer-by-layer fashion. The twin boundary formation and migration energies are found to be 607 and 40 mJ/m, respectively, implying that partial dislocations on twin boundaries will have wide cores and high mobilities. The stress to homogeneously nucleate a partial loop on the boundary of a thick twin is determined to be only 1.4 GPa, indicating that once a deformation twin in Mo reaches a critical thickness, which we estimate to be six layers, it can grow rather easily. Based on simple defect mechanics considerations, we estimate the condition for runaway defect growth requires twin embryo thickness to be tens of layers. Comparing the twinning energy landscape for Mo with those of Al and Cu, we find the former to have a longer ranged interlayer mechanical coupling, which is due to angular bonding and weaker electron screening in the intervening layers. Between Al and Cu, interactions in the former are relatively longer ranged.