Indentation size effect, geometrically necessary dislocations and pile-up effects in hardness testing of irradiated nickel
Indentation size effect, geometrically necessary dislocations and pile-up effects in hardness testing of irradiated nickel
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DOI：
10.1016/j.actamat.2021.116702
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发表时间：
2021-04
期刊：
影响因子：
9.4
通讯作者：
M. Mattucci;I. Cherubin;P. Changizian;T. Skippon;M. Daymond
中科院分区：
文献类型：
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作者：
M. Mattucci;I. Cherubin;P. Changizian;T. Skippon;M. Daymond
基于位错密度，将120 ° C下用6 MeV质子辐照至0.1dpa的商业纯Ni的压痕尺寸效应响应与未辐照的Ni进行了比较。辐照引起的缺陷，其特征在于通过TEM。进行了纳米级和微米级压痕试验。Nix-Gao（NG）模型被应用于确定辐照诱导缺陷引起的体屈服强度的增加，这与Bacon-Kocks-Scattergood（BKS）障碍硬化模型预测的屈服强度增加一致，使用SFT、滑动完美环和无座Frank环的叠加。在NG模型中观察到的非辐照和辐照材料的双线性趋势，表明在“纳米级”制度的压痕变形机制的过渡。如果测量并考虑压痕堆积，则双线性趋势的程度最小化。它示出，在这种材料中，必须小心解释测量时，由于辐照引起的缺陷，从深度浅于10500 nm的测量时，硬度的增加。实验表明，使用应变梯度塑性建模和独立的SEM/EBSD分析，有一个更高的密度的几何必要的位错（GNDs）存在于变形体积下的辐射材料的辐射下的辐射材料相比，在非辐射材料的类似的辐射下，这是从一个更受限制的塑性变形体积下的辐射材料的辐射下的辐射下的辐射材料。有人建议，无柄弗兰克环抑制塑性变形作为障碍位错运动，导致在压头尖端下的变形更局部化。结果是，与体硬度测试相比，使用纳米压痕测量时，辐照和未辐照材料之间的硬度差异更大。GND密度的增加，在纳米压痕的辐照材料可以解释为校正压痕堆积。
The indentation size effect response, based on dislocation density, of commercially pure Ni irradiated at 120°C with 6MeV protons to 0.1dpa, was compared with non-irradiated Ni. Irradiation-induced defects were characterised by TEM. Nano-scale and micro-scale indentation tests were carried out. The Nix-Gao (NG) model was applied to determine the increase in the bulk yield strength arising from irradiation induced defects, which agreed well with the predicted increase in yield strength from the Bacon-Kocks-Scattergood (BKS) obstacle hardening model, using a superposition of SFT, glissile perfect loops and sessile Frank loops. A bi-linear trend was observed in the NG model in both the non-irradiated and irradiated material, indicating a transition in deformation mechanisms for indents in the ‘nano-scale’ regime. The extent of the bi-linear trend was minimized if indentation pile-up was measured and accounted for. It is shown that, in this material, care must be taken when interpreting measurements of the increase in hardness due to irradiation induced defects when measurements are made from depths shallower than ̴500nm. It is experimentally shown using both strain gradient plasticity modelling and independent SEM/EBSD analysis that there is a higher density of geometrically necessary dislocations (GNDs) present in the deformation volume under an indent in the irradiated material when compared to the analogous indent in the non-irradiated material; this results from a more confined plastic deformation volume under the indent in the irradiated material. It is proposed that sessile Frank loops inhibit plastic deformation by acting as obstacles to dislocation motion which results in deformation under the indenter tip being more localised. The result is a larger difference in hardness between the irradiated and non-irradiated material when measured using nanoindentation compared to bulk hardness testing. The increase in GND density in nanoindentation of irradiated material can be accounted for by correcting for indentation pile-up.