Bicontinuous Nanocomposite Refractories

新金属的发现和开发对于需要高强度和延展性的技术应用是至关重要的。在这个节目中，我们探索了一种新型的大块纳米结构金属，这种金属是通过一种称为液态金属合金化的先进加工方法制成的，在这种方法中，钨和钛等难熔金属的合金浸入熔融铜中，在钛溶解的条件下，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。冷却后，复合材料是双连续的，即由两个不同材料的互穿网络组成，一个硬耐火相和一个韧性铜相，结合每种金属的最佳属性，制成一种新型的强韧性材料。在这个项目中，我们将探索制造这些新材料的加工方法，并以系统的方式测试它们的性能，从而了解控制它们行为的基本材料物理。我们将通过学生的参与和课堂资源的开发来传播这种理解。本项目将研究一类新型纳米结构金属的结构/加工/性能关系，该金属具有双连续？亚稳态分解吗?类似的微观结构，但其中一个相是坚硬的难熔金属，如钨，另一个相是韧性金属，如铜。这些材料是用一种我们称之为液态金属合金化（LMD）的新方法制成的，在这种方法中，钛/难熔合金在高温下浸入铜合金熔体中。而钛溶解到铜中，耐火材料在熔体中是不混溶的，所以在浸入过程中，它通过界面扩散重组成一个高度多孔的结构（铜相被去除），其长度范围可从大约50纳米到5000纳米。该过程类似于电化学脱合金，例如用于制造纳米多孔金，不同之处在于LMD中的溶解是由热力学相行为驱动的，而不是电化学溶解。我们的重点是通过这种方法制备的非多孔复合材料的形成动力学和机械性能，这在具有高韧性的超高强度材料的各种应用中具有潜在的实用性。更普遍和根本的是，在LMD过程中自发形成的双连续微观结构是一个在纳米尺度上研究金属材料相变、动力学和力学的平台。除了科学技术驱动之外，该项目还将让学生参与动力学蒙特卡罗模拟代码的开发和传播，用于模拟和研究纳米结构材料中形态演化的动力学，这将补充材料科学动力学和相变的新本科教科书的开发。

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.