Kreuzeder Marius, Abad Manuel-David, Primorac Mladen-Mateo, Hosemann Peter, Maier Verena, Kiener Daniel
Department of Materials Physics, Montanuniversität Leoben, 8700 Leoben, Austria.
Department of Nuclear Engineering, University of California, Berkeley, CA 94720 USA.
J Mater Sci. 2015;50(2):634-643. doi: 10.1007/s10853-014-8622-4. Epub 2014 Sep 30.
Porous materials with ligament sizes in the submicrometer to nanometer regime have a high potential for future applications such as catalysts, actuators, or radiation tolerant materials, which require properties like high strength-to-weight ratio, high surface-to-volume ratio, or large interface density as for radiation tolerance. The objective of this work was to manufacture ultra-fine porous copper, to determine the thermo-mechanical properties, and to elucidate the deformation behavior at room as well as elevated temperatures via nanoindentation. The experimental approach for manufacturing the foam structures used high pressure torsion, subsequent heat treatments, and selective dissolution. Nanoindentation at different temperatures was successfully conducted on the ultra-fine porous copper, showing a room temperature hardness of 220 MPa. During high temperature experiments, oxidation of the copper occurred due to the high surface area. A model, taking into account the mechanical properties of the copper oxides formed during the test, to describe the measured mechanical properties in dependence on the proceeding oxidation was developed. The strain rate sensitivity of the copper foam at room temperature was ∼0.03 and strongly correlated with the strain rate sensitivity of ultra-fine grained bulk copper. Although oxidation occurred near the surface, the rate-controlling process was still the deformation of the underlying copper. An increase in the strain rate sensitivity was observed, comparably to that of ultra-fine-grained copper, which can be linked to thermally activated processes at grain boundaries. Important insights into the effects of oxidation on the deformation behavior were obtained by assessing the activation volume. Oxidation of the ultra-fine porous copper foam, thereby hindering dislocations to exit to the surface, resulted in a pronounced reduction of the apparent activation volume from ~800 to ~50 , as also typical for ultra-fine grained materials.
韧带尺寸处于亚微米到纳米范围的多孔材料在未来应用中具有很高的潜力，如催化剂、致动器或耐辐射材料，这些应用需要诸如高强度重量比、高表面积体积比或大界面密度（如耐辐射性所需）等特性。这项工作的目标是制造超细多孔铜，确定其热机械性能，并通过纳米压痕阐明其在室温及高温下的变形行为。制造泡沫结构的实验方法采用了高压扭转、后续热处理和选择性溶解。在超细多孔铜上成功进行了不同温度下的纳米压痕测试，其室温硬度为220兆帕。在高温实验过程中，由于高表面积，铜发生了氧化。开发了一个模型，该模型考虑了测试过程中形成的氧化铜的力学性能，以描述所测量的力学性能与氧化过程的依赖关系。泡沫铜在室温下的应变速率敏感性约为0.03，与超细晶粒块状铜的应变速率敏感性密切相关。尽管表面附近发生了氧化，但速率控制过程仍然是下层铜的变形。观察到应变速率敏感性增加，与超细晶粒铜相当，这可能与晶界处的热激活过程有关。通过评估激活体积，获得了关于氧化对变形行为影响的重要见解。超细多孔铜泡沫的氧化阻碍了位错逸出到表面，导致表观激活体积从约800显著减小到约50，这也是超细晶粒材料的典型特征。
