Abstract

We investigated the analytic relation between hardness and compressive yield stress using an expanding cavity model (ECM) for nanoporous gold (np-Au). We prepared three np-Au samples with ligament sizes 30.61, 59.36 and 116.33 nm by free-corrosion dealloying and post heat treatment. The indentation contact morphology was examined to estimate the hardness accurately from the nanoindentation load-depth curve. Unlike conventional dense metals, the deformation was confined to the projected contact area, and the center of the residual impression was dominated by densification. The projected contact area estimated by the Oliver–Pharr method was overestimated, so that a new contact area function was proposed that considered the indentation contact morphology of np-Au. It was confirmed that a hardness value taking into account the indentation contact morphology of np-Au matches well with the hardness derived by direct measurement of the residual impression. We modeled the ratio of hardness to compressive yield stress for np-Au using an ECM. The scaling factors, which represent the extra strain-hardening in the core in the ECM, were analyzed for np-Au and dense metals. An ECM that better matches np-Au is suggested based on the scaling factor resulting from densification beneath the indenter.

Graphic abstract

中文翻译：

---

通过纳米压痕对纳米多孔金的压缩特性：基于膨胀腔模型的解析方法

摘要

我们使用纳米孔金（np-Au）的膨胀腔模型（ECM）研究了硬度与压缩屈服应力之间的解析关系。我们通过自由腐蚀脱合金和后热处理制备了三个韧带尺寸为30.61、59.36和116.33 nm的np-Au样品。检查压痕接触形态，以从纳米压痕载荷-深度曲线准确估计硬度。与传统的致密金属不同，变形仅限于投影接触面积，而残留压痕的中心则由致密化决定。通过Oliver-Pharr方法估计的预计接触面积被高估了，因此提出了一种新的接触面积函数，该函数考虑了np-Au的压痕接触形态。证实了考虑到np-Au的压痕接触形态的硬度值与通过直接测量残余压痕得到的硬度很好地匹配。我们使用ECM对np-Au的硬度与压缩屈服应力之比进行建模。对于np-Au和致密金属，分析了比例因子，这些比例因子代表了ECM核心中的额外应变硬化。根据压头下方致密化产生的缩放系数，提出了与np-Au更好匹配的ECM。

图形摘要