Surface-Condition-Dependent Deformation Mechanisms in Lead Nanocrystals

Abstract

Serving as nanoelectrodes or frame units, small-volume metals may critically affect the performance and reliability of nanodevices, especially with feature sizes down to the nanometer scale. Small-volume metals usually behave extraordinarily in comparison with their bulk counterparts, but the knowledge of how their sizes and surfaces give rise to their extraordinary properties is currently insufficient. In this study, we investigate the influence of surface conditions on mechanical behaviors in nanometer-sized Pb crystals by performing in situ mechanical deformation tests inside an aberration-corrected transmission electron microscope (TEM). Pseudoelastic deformation and plastic deformation processes were observed at atomic precision during deformation of pristine and surface-oxidized Pb particles, respectively. It is found that in most of the pristine Pb particles, surface atom diffusion dominates and leads to a pseudoelastic deformation behavior. In stark contrast, in surface-passivated Pb particles where surface atom diffusion is largely inhibited, deformation proceeds via displacive plasticity including dislocations, stacking faults, and twinning, leading to dominant plastic deformation without any pseudoelasticity. This research directly reveals the dramatic impact of surface conditions on the deformation mechanisms and mechanical behaviors of metallic nanocrystals, which provides significant implications for property tuning of the critical components in advanced nanodevices.

Remarkable Wear Resistance in a Complex Concentrated Alloy with Nanohierarchical Architecture and Composition Undulation

“…In stark contrast, the intrinsic heterostructures in the NiX allow the activation of multiple depth-dependent deformation mechanisms upon wear, which promotes the formation of gradient recrystallized tribo-layer. Furthermore, when the grain size is reduced to the nanometer scale, the unusual interface-dependent deformation processes may be triggered [ 9 , 52 ]. Figure 4 E to G shows the deformation microstructures extending from the depth direction of the worn surface to 200 nm (NC tribo-layer), 700 nm (top of the UFG tribo-layer), and 1.6 μm (bottom of the UFG tribo-layer), respectively.…”

Nb_0.8CoSb ordering transformation caused by <i>in situ</i> heating-induced Nb diffusion

“…1 引 言 随着信息技术的迅速发展和能源需求的不断增长，能够改变材料结构且伴 随能量转移的固态相变引起了人们广泛关注，深入了解材料的固态相变过程及 其微观机理对于理解和调控材料性能至关重要。固态相变是指材料在温度、压 力或其他刺激驱动下，从一种晶体结构转变为另一种晶体结构的现象。这一结 构转变过程往往伴随着材料性质的变化以及能量的转移。近几十年来，人们对 固态相变的关注不断增加，其在结构材料 [1][2][3][4] 、能源材料 [5][6][7] 、催化材料 [8,9] 以及 光学材料 [10,11] 等领域中的作用日益凸显。 赫斯勒合金一类是重要的三元或多元金属间化合物，具有多种独特的相变 特性，包括铁磁相变 [12] 、量子相变 [13] 等。其中，Ni 2 MnGa [14] 、Ni 2 FeGa [15] 等赫 斯勒合金具有马氏体相变特性，且在其马氏体状态下，能够产生由磁场诱发应 变的形状记忆效应，因此这类材料成为当前国际上备受关注的新型磁性功能材 料之一。此外，通过调节 Ni-Mn-X(X = In, Sn, Sb)合金的成分，也能够引发 该系列合金在降温过程中的马氏体转变 [16] ，使合金处于磁性不均匀状态，呈现 出丰富的物理性质，如磁热效应 [17,18] 和交换偏置现象 [19,20] 等。这些效应在室温 磁致冷以及信息存储等方面都有着广泛的应用前景。 除了马氏体相变，在热电材料领域 Xia 和 Nan 等 [21,22] 的热电性能 [23,24] 。并且，随着 Nb 空位的减少，漫散带强度逐渐降低，在 Nb 空 位浓度降低至仅有 16%的 Nb 0.84 CoSb 中，选区电子衍射花样中的漫散带完全消 失，取而代之的是代表调制结构的超结构衍射点 [21] 。这一发现揭示了 Nb 空位 浓度在诱导 Nb 0.8 CoSb 发生相变过程中的重要作用。 成分导致的相变容易通过传统的化学合成实验完成，但要探究中间的反应 过程、理解反应机理很难利用传统的表征手段实现 [25,26] 。本文中我们发挥原位 球差矫正电镜(TEM)高空间和时间分辨率的优势，通过高温元素扩散在动态 Further comparative analysis revealed significant differences…”