Vacancy Engineering for Enhanced Strength and Toughness of Metals

增强金属强度和韧性的空位工程

• 批准号: 1609060
• 负责人: Md Haque
• 金额: $ 32.5万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1609060&HistoricalAwards=false
• 关键词: Vacancy; Engineering; Enhanced; Strength; Toughness

1. Nontechnical Abstract Strength (ability to bear mechanical load) and toughness (ability to resist fracture) are desired in civil and transportation infrastructure, manufacturing and processing, and bio-medical implants to make them stronger, safer, and lighter and energy efficient. Unfortunately, strength and toughness in metals are mutually exclusive - a fundamental challenge that remains to be resolved because the mechanism that controls strength in metals is inversely coupled with toughness. This research project aims to introduce a new type of mechanism, where atomic scale vacancies interact with existing defects to induce decoupling of strength and toughness. Such vacancy-defect interaction is not well understood because in conventional metals, vacancies do not play dominant roles. In addition, these mechanisms are strongly influenced by the internal structure and existing defect distribution in the metal as well as temperature. The experiments will be performed inside high-resolution microscopes, so the role of different deformation mechanisms can be seen in real time as strength and toughness are controlled and measured. The scientific outcome of this research will be new knowledge in atomic scale vacancy - defect interactions, which will be demonstrated through technological innovation in metals that are both strong and tough. Graduate and undergraduate students will be trained in crosscutting disciplines of metallurgy, mechanics, nanofabrication and microscopy to solve this highly coupled research problem. Academic outreach activities will be performed to attract the next generation workforce towards materials science & engineering. 2. Technical AbstractStrength of metals originates from their capability of suppressing dislocation motion or plastic deformation. Toughness, on the other hand, requires large amount of plastic work before fracture. Because of such conflict, they are mutually exclusive. The current paradigm is to optimize, or in other words, compromise between strength and toughness. Contrarily, this research aims to maximize strength and toughness through synergistic multi-scale defect interactions (0D: vacancy, 1D: dislocations and 2D: grain/twin boundaries). Here, dislocation confinement in nano-crystalline metals is exploited to achieve high strength. At the same time, point defects (vacancies) are generated at ambient conditions, which facilitate diffusion-based plasticity without unlocking the dislocations. The net result is the unique co-existence of suppressed dislocation activities and pronounced diffusional plasticity without any change in grain size. This research is based on the hypothesis that it is possible to have both dislocation-based strength and diffusion-based deformability in the same grain at the same time and at ambient temperature. A unique material processing technique with temperature-current-stress synergy is proposed to generate the required vacancy concentration. This leads to a transformative concept; a three-way interaction among three dimensions of defects to maximize both strength and toughness. The nanoscale grain boundaries will lead to very high strength by impeding dislocation motion. The lack of ductility arising from small grains is removed by vacancies through diffusional plasticity in the grain boundaries. Finally, scalability of the proposed concept in meso and macroscopic manufacturing processing will be studied for feasibility in real life applications.

1.在民用和交通基础设施、制造和加工以及生物医学植入物中需要非技术抽象强度(承受机械载荷的能力)和韧性(抗骨折能力)，以使其更坚固、更安全、更轻和更节能。不幸的是，金属的强度和韧性是相互排斥的--这是一个有待解决的根本挑战，因为控制金属强度的机制与韧性是反向耦合的。本研究项目旨在引入一种新的机制，在这种机制中，原子尺度的空位与现有的缺陷相互作用，导致强度和韧性的解耦。这种空位-缺陷相互作用并没有被很好地理解，因为在传统金属中，空位并不起主导作用。此外，这些机制还受到金属内部结构和存在的缺陷分布以及温度的强烈影响。实验将在高分辨率显微镜内进行，因此在控制和测量强度和韧性时，可以实时看到不同变形机制的作用。这项研究的科学成果将是原子尺度的空位-缺陷相互作用的新知识，这将通过金属的技术创新得到证明，这些金属既强大又坚韧。研究生和本科生将接受冶金、力学、纳米加工和显微镜等交叉学科的培训，以解决这一高度耦合的研究问题。将开展学术外展活动，吸引材料科学与工程领域的下一代劳动力。2.技术摘要金属的强度源于其抑制位错运动或塑性变形的能力。另一方面，韧性在断裂前需要大量的塑性加工。由于这种冲突，它们是相互排斥的。当前的模式是优化，或者换句话说，在力量和韧性之间妥协。相反，本研究旨在通过多尺度缺陷的协同作用(0D：空位、1D：位错和2D：晶界/孪晶界)来最大化强度和韧性。在这里，利用纳米晶体金属中的位错限制来获得高强度。同时，在环境条件下会产生点缺陷(空位)，这有助于在不解锁位错的情况下进行基于扩散的塑性。最终结果是在不改变晶粒度的情况下，被抑制的位错活动和显著的扩散塑性共存。这项研究是基于这样的假设，即在相同的时间和环境温度下，在同一晶粒中可能同时具有基于位错的强度和基于扩散的变形能力。提出了一种独特的材料加工技术，它具有温度-电流-应力协同作用，可以产生所需的空位浓度。这导致了一个变革性的概念；缺陷的三个维度之间的三向交互作用，以最大限度地提高强度和韧性。纳米晶界会阻碍位错的运动，从而导致很高的强度。细晶引起的塑性不足通过晶界的扩散塑性被空位消除。最后，将研究提出的概念在细观和宏观制造过程中的可扩展性，以期在实际应用中具有可行性。