Experimental and Theoretical Investigations of Gum Metal

技术概述：树胶金属是钛-铌基合金，具有显著的机械性能，包括超弹性、超高强度、大的延展性、零热膨胀系数和在一定温度范围内保持不变的弹性常数。令人惊讶的是，这些材料的塑性似乎既不是由位错运动引起的，也不是由相变引起的。相反，这些材料似乎以其理想的强度变形。如果是这样的话，这些合金代表了一种新型的结构合金。它们不同寻常的机械行为与强烈的弹性各向异性有关，这种各向异性随着合金成分的相变而发展。这种各向异性允许容易的位错钉扎，位错核的极端扩展，并在抑制相变方面发挥作用，否则可能会削弱合金。该项目涉及两个主要目标。首先，它的目的是从实验上了解这些不寻常的合金中控制塑性的精确机制。这一理解将通过纳米压痕和透射电子显微镜实验相结合来发展。其次，该项目将开发能够解释观测到的变形行为的理论工具和想法。最初的理论研究将集中在Gum Metals中位错的结构，特别关注扩散位错核心和位错核心重叠的含义。这样获得的理解将被用来识别具有类似于胶金属的变形潜力的新合金系统。非技术摘要：材料的理想强度是材料在永久变形之前所能承受的最大可能载荷。通常，一种材料的观测强度是其理想强度的1/100或更低，这在很大程度上是因为被称为位错的缺陷能够在远低于理想强度的应力下在晶体中移动。这一认识处于现代冶金学的核心，并指导着大多数结构合金的发展。金属胶是一种新近发现的钛-铌基合金，具有一系列显著的机械性能。最显著的特征是，Gum Metals似乎通过独特的无位错变形机制以理想的强度变形。这项研究的目的是识别和理解导致金属胶非凡性能的变形机制(S)，并利用这种理解来发展支配金属胶行为的冶金原理。然后，这些原理将被用来寻找表现出与金属胶相似的机械性能的新材料。新冶金原理的确定有可能使一类新的结构材料的开发成为可能。这种材料将影响包括交通和能源发电在内的广泛技术。正在攻读博士学位的学生将进行大部分研究。旨在向高中物理学生介绍材料科学和工程学科的课程材料将被开发，并以结构材料在滑板运动中的作用为例-滑板是一项受青少年欢迎的运动。

TECHNICAL SUMMARY: Gum metals are Ti-Nb based alloys that display remarkable mechanical properties, including super-elasticity, super-strength, large ductility, zero coefficient of thermal expansion and elastic constants that remain constant over a range of temperatures. Surprisingly, plasticity in these materials appears to be mediated neither by dislocation motion nor by phase transformation. Instead, these materials appear to deform at their ideal strength. If so, these alloys represent a new type of structural alloy. Their unusual mechanical behavior is linked to a strong elastic anisotropy that develops as the composition of the alloy is driven towards a phase transformation. This anisotropy allows for easy dislocation pinning, the extreme spreading of the dislocation cores, and plays a role in the suppression of phase transformations that might otherwise weaken the alloys. The project involves two primary goals. First it aims to understand experimentally the precise mechanism governing plasticity in these unusual alloys. This understanding will be developed using a combination of nanoindentation and transmission electron microscopy experiments. Second, the project will develop theoretical tools and ideas capable of explaining the observed deformation behavior. Initial theoretical studies will focus on the structure of dislocations within Gum Metals paying particular attention to the implications of spread dislocation cores and dislocation core overlap. The understanding so obtained will be used to identify new alloys systems with the potential to deform similarly to Gum Metals.NON-TECHNICAL SUMMARY: The ideal strength of a material is the largest possible load the material can withstand before becoming permanently deformed. Typically, the observed strength of a material is 1/100th or less of its ideal strength, largely because defects known as dislocations are able to move throughout the crystal at stresses well below the ideal strength. This understanding lies at the heart of modern metallurgy, and guides the development of most structural alloys. Gum Metal is a recently discovered Ti-Nb based alloy with a long list of remarkable mechanical properties. The most striking characteristic is that Gum Metal appears to deform at ideal strength via a unique dislocation-free deformation mechanism. The goal of this research is to identify and understand the deformation mechanism(s) that gives rise to the remarkable properties of Gum Metal, and to use this understanding to develop the metallurgical principles that govern Gum Metal behavior. These principles will then be used to search for new materials that display mechanical properties similar to Gum Metal. The identification of novel metallurgical principles has the potential to enable the development of a new class of structural materials. Such materials would impact a broad range of technologies including transportation and energy generation. Students working towards their doctoral degrees will conduct much of the research. Course materials geared toward introducing high school physics students to the discipline of materials science and engineering will be developed and exemplified by the role of structural materials in the sport of skateboarding---a sport popular with teenagers.