Bicontinuous Nanocomposite Refractories

新金属的发现和发展对于需要高强度和高延展性的技术应用是至关重要的。在这个项目中，我们探索了一种新的块状纳米结构金属，这种金属是通过一种名为液态金属去合金化的先进加工方法制造的，在这种方法中，难熔金属(如钨和钛)的合金被浸入熔化的铜中，在这种条件下，钛被溶解，难熔金属重新组织成纳米级网络，一种韧带只有几百个原子的桁架网络。在冷却时，复合材料是双连续的，即由两个相互渗透的不同材料组成的网络，一个硬质耐火相和一个延性铜相，结合了每种金属的最佳属性，形成了一种新型的强韧材料。在这个节目中，我们将探索制造这些新材料的加工方法，并系统地测试它们的性能，以了解支配它们行为的基本材料物理。我们将通过学生参与和课堂资源的开发来传播这一理解。技术总结本项目将研究一类新的纳米结构金属的结构/工艺/性能关系，这种金属具有双连续的？旋节分解？样的微结构，但其中一个相是坚硬的难熔金属，如钨，而另一个相是延展性金属，如铜。这些材料是用一种我们称为液态金属脱合金法(LMD)的新方法制造的，在这种方法中，钛/难熔合金在高温下浸入铜合金熔体中。钛溶解到铜中，而耐火材料在熔体中不溶于水，因此在浸泡过程中，它通过界面扩散重新组织成高度多孔的结构(如果要去除铜相)，长度从大约50 nm到5000 nm可调。除了在LMD中的溶解是由热力学相行为驱动的，而不是电化学溶解，这一过程类似于电化学去合金化，例如用于生成纳米多孔金。本文重点研究了这种方法制备的无孔复合材料的形成动力学和力学性能，这些材料在高韧性超强材料的各种应用中具有潜在的应用价值。更广泛和根本的是，在LMD过程中自发形成的双连续微结构是在纳米尺度上检验金属材料的相变、动力学和力学的平台。除了科学技术的驱动力，这个项目还将让学生参与开发和传播动力学蒙特卡罗模拟程序，用于模拟和研究纳米结构材料中的形态演变动力学，这将补充材料科学的新本科生教科书的开发。

Non-Technical SummaryThe discovery and development of new metals is critical for technical applications where high strength and ductility are necessary. In this program, we explore a new class of bulk nanostructured metals made by an advanced processing method called liquid metal dealloying, in which an alloy of a refractory metal such as tungsten and titanium is immersed into molten copper under conditions in which the titanium is dissolved away and the refractory metal re-organizes itself into a nanoscale network, a kind of truss network whose ligaments are only a few hundred atoms across. Upon cooling, the composite material is bicontinuous, i.e. comprised of two interpenetrating networks of distinct materials, a hard refractory phase and a ductile copper phase, combining the best attributes of each metal to make a novel strong and ductile material. In this program, we will explore processing methods to make these new materials and test their properties in systematic ways so as to understand the fundamental materials physics that govern their behavior. We will disseminate this understanding via student participation and the development of classroom resources.Technical SummaryThis project will examine the structure/processing/property relationship of a new class of nanostructured metals, which possess a bicontinuous ?spinodal decomposition?-like microstructure, but where one phase is a hard refractory metal such as tungsten and the other phase is a ductile metal such as copper. These materials are made using a new method we call liquid metal dealloying (LMD), in which titanium/refractory alloys are immersed in copper alloy melts at elevated temperatures. Whereas titanium dissolves out into the copper, the refractory is immiscible in the melt so during immersion it reorganizes via interface diffusion into a highly porous structure (were the copper phase to be removed), with a tunable lengthscale from approximately 50 nm to 5000 nm. The process is akin to electrochemical dealloying, such as is used to create nanoporous gold, except that dissolution in LMD is driven by thermodynamic phase behavior, and not electrochemical dissolution. Our focus here is on the kinetics of formation and the mechanical properties of non-porous composites fabricated by this method, which have potential utility in the diverse number of applications for ultra-strong materials with high toughness. More generally and fundamentally, the spontaneous formation of the bicontinuous microstructure during LMD is a platform on which to examine phase transformations, kinetics, and mechanical of metallic materials at the nanoscale. In addition to the scientific technology drivers, this program will involve students in the development and dissemination of kinetic Monte Carlo simulation code for the simulation and study of the kinetics of morphological evolution in nanostructured materials that will complement the development of a new undergraduate textbook on Kinetics and Phase Transformations for Materials Science.