Size Effects in the Mechanical Properties of Bulk Bicontinuous Ta/Cu Nanocomposites Made by Liquid Metal Dealloying
Size Effects in the Mechanical Properties of Bulk Bicontinuous Ta/Cu Nanocomposites Made by Liquid Metal Dealloying
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DOI：
10.1002/adem.201500219
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发表时间：
2016-01-01
影响因子：
3.6
通讯作者：
Erlebacher, Jonah
中科院分区：
文献类型：
--
作者：
McCue, Ian;Ryan, Stephen;Erlebacher, Jonah
微观结构长度尺度的控制是坚韧金属设计和制造的核心。[1-3]金属中的大多数强化策略，例如沉淀硬化、晶粒细化和加工硬化，均匀地控制本征微观结构，并且通常起到抑制位错运动的作用。这些方法增加了移动位错所需的应力，但它们也倾向于降低延展性。当物理尺寸减小到低于材料内部微观结构障碍时，许多有趣的尺寸效应开始发挥作用。例如，金属薄膜的强度与薄膜厚度成反比，[4]无位错的晶须比传统的金属丝强许多倍，[5]金属的硬度随着压痕尺寸的减小而增加，[6]微柱的抗压强度比在体中测量的要大得多。[7-10]人们普遍认识到，在与自由表面的相互作用可能导致位错饥饿、源截断或堆积的折合体积中，位错活动不同。[11-14]虽然尺寸相关强化的确切起源仍然存在争议，并且可能因系统而异，但小即是强的实验观察显示了有前途的新金属材料。如何将这些力学响应转化为块体材料是一个迫切需要考虑的问题。其中一类表现出尺寸效应的块体-纳米结构材料是脱合金金属，由于其易于制造，纳米多孔金（NPG）是其模型系统。[15-19] NPG是通过电化学去合金化制成的，将富含Ag的Ag-Au母合金浸入酸中，选择性地溶解掉银原子，同时留下金原子沿着金属/电解质界面扩散，自组织成具有明确长度尺度（例如，平均韧带或孔径）的多孔结构。[20-22]脱合金金属在小于母合金晶粒尺寸的尺度上是多孔的，并且脱合金相是相互连接的梁的复杂的3D网络，没有任何在脱合金之前不存在的晶体缺陷。压痕和微柱压缩测试表明，具有较小的特征尺寸，单个NPG韧带的强度接近金的理论强度，但批量样品的测试通常会导致脆性破坏，这是大多数纳米多孔金属（NPMs）的共同特征。[23 Weissmuller最近表明，如果用聚合物浸渍纳米多孔金的孔，那么与单独的多孔组分相比，复合材料的机械性能大大改善，在压缩中具有良好的强度和高塑性应变。[25]电化学脱合金材料的挑战在于它们往往是贵金属，其低熔点使得难以制造用于结构应用的坚固材料。加藤介绍了一种可能的解决方案，即开发一种新的去合金化技术，即液态金属去合金化（LMD），该技术使用熔融金属作为介质，选择性地溶解其中一种合金成分。[26-29]通过这一过程，他成功地制造了多孔Ti，Cr，Fe，Si和Nb;然而，
Control of microstructural length scales is central to the design and fabrication of strong and tough metals.[1-3] Most strengthening strategies in metals, such as precipitation hardening, grain refinement, and work hardening, uniformly control the intrinsic microstructure and generally work to inhibit dislocation motion. These methods increase the stress required to move dislocations but they also tend to lower ductility. As the physical dimensions are reduced below that of a material's internal microstructural obstacles, a number of interesting size effects come into play. For example, the strength of metallic thin films scales with the inverse of the film thickness,[4] dislocation-free whiskers are many times stronger than conventional wires,[5] the hardness of metals increases with decreasing indentation size,[6] and the compressive strength of micropillars is much greater than that measured in the bulk.[7-10] There is general recognition that dislocation activity is different in reduced volumes where interactions with free surfaces can lead to dislocation starvation, source truncation, or pileup.[11-14] Although the exact origin of size-dependent strengthening is still debated and may vary from system to system, experimental observations of smaller-is-stronger show promising new metallic materials. It is compelling to consider how to translate these kinds of mechanical responses into bulk materials.One class of bulk-nanostructured materials that exhibit size effects on their mechanical properties are dealloyed metals, for which nanoporous gold (NPG) is a model system due to its ease of fabrication.[15-19] NPG is made via electrochemical dealloying, immersing a Ag-rich Ag-Au parent alloy in acid, selectively dissolving away the silver atoms while leaving the gold atoms behind to diffuse along the metal/electrolyte interface, self-organizing into a porous structure with welldefined length scales (eg, average ligament or pore diameter).[20-22] Dealloyed metals are porous at scales smaller than the parent alloy grain size and the dealloyed phase is a complex, 3D network of interconnected beams without any crystal defects that did not exist prior to dealloying. Indentation and micropillar compression tests show that with smaller feature size, the strength of individual NPG ligaments approach the theoretical strength of gold, but testing of bulk samples generally results in brittle failure, a feature common to most nanoporous metals (NPMs).[23, 24] Weissmuller recently showed that if the pores of nanoporous gold are impregnated with a polymer, then the mechanical properties of the composite are greatly improved compared to the porous component alone, having both good strength and high plastic strain in compression.[25] The challenge with electrochemically dealloyed materials is that they tend to be precious metals, whose low melting points make it difficult to make strong materials for structural applications. Kato introduced a possible solution by developing a new dealloying technique, liquid metal dealloying (LMD), which uses a molten metal as a medium to selectively dissolve one of the alloying components.[26-29] Through this process, he has successfully fabricated porous Ti, Cr, Fe, Si, and Nb; however, he