The hardness and modulus of polycrystalline beryllium from nano-indentation
The hardness and modulus of polycrystalline beryllium from nano-indentation
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DOI：
10.1016/j.ijplas.2018.12.008
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发表时间：
2019-05
影响因子：
9.8
通讯作者：
V. Kuksenko;Steve Roberts;E. Tarleton
中科院分区：
文献类型：
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作者：
V. Kuksenko;Steve Roberts;E. Tarleton
采用纳米压痕法对四种不同纯度的工业铍进行了性能比较。在所有样品中观察到硬度的极高变化，这掩盖了样品之间的差异。结合SEM/EBSD测量的纳米压痕数据的分析表明，压痕晶粒的晶体取向是硬度变化的主要来源，当压痕方向接近铍的[0001] c轴时，硬度比沿着[11 2 <$0]或[1 1 <$00]方向压痕时高2.5倍。在“软”取向方面观察到测试等级之间最显著的差异：与纯核等级相比，不太纯的结构等级的硬度高15-30%。晶体塑性有限元（CPFEM）模拟表明，铍的硬度各向异性是如何产生的塑性变形的各向异性。实验和模拟还表明，局部塑性变形的表面周围的压痕（堆积或下沉）是高度晶体学依赖：在压痕到“软”的方向，堆积占主导地位的接触面积增加，而下沉的行为是占主导地位的压痕到“硬”的方向减少接触面积。这意味着，使用标准Oliver-Pharr方法，根据压头位移和压头轮廓计算的硬度值（不考虑堆积/下沉效应）将是不正确的。应用并比较了几种接触面积修正方法。与此相反，压痕模量是相似的所有调查等级，并没有发现有任何强烈的晶体学依赖性。晶体塑性有限元分析表明，这是由于压头与样品之间弹性相互作用的复杂三维性质，而且对于选定的压痕深度，弹性相互作用体积远大于材料的粒度。
Nanoindentation was used to compare properties of four industrial beryllium grades with different purity. An extremely high variation of hardness was observed in all samples which obscured differences between samples. Analysis of the nanoindentation data in combination with SEM/EBSD measurements demonstrated that the crystallographic orientation of the indented grain was the major source of the wide variation in hardness, which was 2.5 times higher when the indentation direction was close to the [0001] c-axis of beryllium compared to indentation along the [11 2¯ 0] or [1 1¯ 00] directions. The most noticeable difference between tested grades were observed for the “soft” orientations: hardness of less pure structural grades was 15–30% higher compared to the pure nuclear grade. Crystal plasticity finite-element (CPFEM) simulations indicated how the hardness anisotropy of beryllium arises from the anisotropy in the plastic deformation. Experiments and simulations also demonstrated that localised plastic deformation of the surface around the indent (pile-up or sink-in) was highly crystallographically dependent: during indentation into “soft” orientations, pile-up dominated increasing the contact area; while sink-in behaviour was dominant during indentation into “hard” orientation reducing the contact area. This implies that the hardness values calculated from indenter displacement and indenter profile using the standard Oliver-Pharr approach, without considering pile-up/sink-in effects, will be incorrect. Several contact area correction methods were applied and compared. In contrast the indentation modulus was similar for all investigated grades and was not found to have any strong crystallographic dependence. Crystal plasticity finite element analysis indicates that this is due to the complex 3-dimensional nature of the elastic interaction between the indenter and the sample, and also since, for the chosen indentation depth, the elastic interaction volume is much larger than the materials’ grain size.