On the crystallographic anisotropy of nanoindentation in pseudoelastic NiTi
On the crystallographic anisotropy of nanoindentation in pseudoelastic NiTi
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DOI：
10.1016/j.actamat.2012.09.081
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发表时间：
2013-01-01
期刊：
影响因子：
9.4
通讯作者：
Eggeler, Gunther
中科院分区：
文献类型：
--
作者：
Pfetzing-Micklich, Janine;Somsen, Christoph;Eggeler, Gunther
我们使用带有Berkovich尖端的纳米压头研究了两种具有B2晶体结构的多晶金属间化合物NiAl和NiTi的局部力学性能。我们使用取向成像扫描电镜选择了相应数量的晶粒，这些晶粒尺寸合适，表面法线平行于< 0 0 1 >,< 1 0 1 >和< 1 1 1 >。作为一个引人注目的新结果，我们发现镍钛具有很强的晶体取向依赖性。这种各向异性在NiAl的情况下不那么明显。对于NiTi，施加特定压痕深度所需的压痕力在< 0 0 0 1 >方向上最大，在< 1 1 1 >方向上最小。我们考虑了从凹痕下方的横截面得到的透射电子显微镜结果，并使用分子动力学模拟和解析剪切应力计算来讨论如何在基本变形和转变过程中解释这种差异，与位错塑性（NiAl和NiTi）有关，以及在应力诱导下马氏体（NiTi）的形成和生长。结果表明：纳米压痕过程中镍钛的晶体各向异性受马氏体相变的取向依赖性控制；位错塑性似乎不太重要。(c) 2012材料学报Elsevier Ltd.出版。版权所有。
We use a nanoindenter with a Berkovich tip to study local mechanical properties of two polycrystalline intermetallics with a B2 crystal structure, NiAl and NiTi. We use orientation imaging scanning electron microscopy to select a relevant number of grains with appropriate sizes and surface normals parallel to < 0 0 1 >, < 1 0 1 > and < 1 1 1 >. As a striking new result, we find a strong crystallographic orientation dependence for NiTi. This anisotropy is less pronounced in the case of NiAl. For NiTi, the indentation force required to impose a specific indentation depth is highest for indentation experiments performed in the < 0 0 1 > direction and lowest along the < 1 1 1 > direction. We consider transmission electron microscopy results from cross-sections below the indents and use molecular dynamics simulations and resolved shear stress calculations to discuss how this difference can be accounted for in terms of elementary deformation and transformation processes, related to dislocation plasticity (NiAl and NiTi), and in terms of the stress-induced formation and growth of martensite (NiTi). Our results show that the crystallographic anisotropy during nanoindentation of NiTi is governed by the orientation dependence of the martensitic transformation; dislocation plasticity appears to be less important. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.