Systematic length scale studies are required for understanding effects of microstructural features that determine the mechanical properties of hierarchical materials. Recent advances in spherical indentation stress-strain protocols have made it possible to characterize the local mechanical responses at different length scales, from hundreds of nanometers to hundreds of microns. In this paper, two model martensitic steels Fe-5.1Ni-0.13C (wt.%) and Fe-5.0Ni-0.30C (wt.%) with different carbon contents were investigated using spherical nanoindentation stress-strain curves to quantify the mechanical behavior of lath martensite at multiple length scales using different spherical indenter tip radii. The indentation yield strength is dominated by the nanoscale defect structure for all indenter radii (1 μm, 16 μm and 100 μm) and does not exhibit any discernable size effect in the measured yield strengths at different length scales. The work hardening rates measured in the indentation tests at the different length scales coincide until the indentation zones grow large enough, so that a significant increase of work hardening occurs which is attributed to the presence of high-angle block boundaries in the indentation probed volumes. Characteristic pop-ins were observed in the indentations performed with the 1 μm and 16 μm indenter tip sizes and have been attributed to the interaction of dislocations with lath boundaries and their eventual transmission. In addition, the correlations between the properties measured from these indentation protocols and those measured in uniaxial tensile tests are critically examined.

需要进行系统的长度尺度研究，以了解决定分层材料机械性能的微观结构特征的影响。球形压痕应力-应变协议的最新进展使得表征从数百纳米到数百微米的不同长度尺度的局部机械响应成为可能。本文采用球形纳米压痕应力-应变曲线研究了两种碳含量不同的两种模型马氏体钢Fe-5.1Ni-0.13C（wt。％）和Fe-5.0Ni-0.30C（wt。％）不同球形压头尖端半径的板条马氏体在多个长度尺度上的行为 对于所有压头半径（1μm，16μm和100μm），并且在不同长度尺度下所测得的屈服强度没有表现出任何明显的尺寸效应。在压痕测试中以不同的长度比例测量的加工硬化率保持一致，直到压痕区域变得足够大为止，从而使加工硬化显着增加，这归因于在压痕探测体积中存在高角度的块边界。在压痕尺寸为1μm和16μm的压痕中观察到了特征弹起，并归因于位错与板条边界的相互作用以及它们最终的传递。此外，还严格检查了从这些压痕方案测得的性能与在单轴拉伸试验中测得的性能之间的相关性。