Abstract The paper presents a comparative study of different nanoindentation methods as applied to the ferritic/martensitic steels T91 and Eurofer97, here investigated in the non-irradiated reference state, but envisaged as structural materials for nuclear fission and fusion applications, respectively. Depth-controlled single cycle measurements at various indentation depths, force-controlled single cycle, force-controlled progressive multi-cycle measurements, and continuous stiffness measurements (CSM) using a Berkovich tip at room temperature have been combined to determine the indentation hardness and the elastic modulus, and to assess the robustness of the different methods in capturing the indentation size effects (ISE) of those steels. The Nix−Gao model is found inappropriate because it does not account for the breakdown of the scaling regime at small indentation depths that is linked to the extremely high density of dislocations associated with martensitic lath boundary misorientation. A generalization of the Nix–Gao model is therefore developed which allows the prediction of the dislocation densities in the lath structure in accordance with neutron diffraction results. Amplitude and frequency of the CSM oscillations influence the ISE observed. Differences of the microstructure-based parameters describing the ISE of quasi-static and dynamic measurements on T91 and Eurofer97 may reflect differences in the associated deformation mechanisms and histories.

中文翻译：

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铁素体/马氏体钢的压痕尺寸效应：对比实验和建模研究

摘要 本文对应用于铁素体/马氏体钢 T91 和 Eurofer97 的不同纳米压痕方法进行了比较研究，这里在未辐照参考状态下进行研究，但分别设想作为核裂变和聚变应用的结构材料。不同压痕深度的深度控制单循环测量、力控制单循环、力控制渐进多循环测量和在室温下使用 Berkovich 尖端的连续刚度测量 (CSM) 已被结合来确定压痕硬度和硬度。弹性模量，并评估不同方法在捕捉这些钢的压痕尺寸效应 (ISE) 方面的稳健性。Nix-Gao 模型被认为是不合适的，因为它没有考虑小压痕深度处缩放制度的破坏，这与与马氏体板条边界错误相关的极高密度的位错有关。因此，开发了 Nix-Gao 模型的推广，它允许根据中子衍射结果预测板条结构中的位错密度。CSM 振荡的幅度和频率影响观察到的 ISE。描述 T91 和 Eurofer97 准静态和动态测量 ISE 的基于微观结构的参数的差异可能反映了相关变形机制和历史的差异。