Accelerated Sintering in "Nano-Duplex" Dual Phase Nanostructured Alloys

几十年来，研究人员一直在追求所谓的“纳米晶”合金作为下一代材料。这些材料在几十个原子的尺度上具有非常精细的内部结构，并且在强度、耐磨性、耐腐蚀性和许多其他功能特性方面表现出显着的改善。虽然实验室工作已经成功地生产了纳米晶体材料的小样品，但这还没有转化为“大块”合金的商业规模生产，也就是说，大到足以制造工程部件的材料。该项目正在开发一种科学方法来解决这些先进材料的可扩展性问题。它探索了纳米结构粉末的合金化科学，这些粉末可以在高温下固结成大块部件，同时仍然保持纳米晶体结构。在科学上，该项目旨在深入了解纳米晶合金粉末，其结构和可加工性。本课题将实验与仿真相结合，重点研究基于金属钨的模型合金系统，该系统广泛应用于切削工具和加工设备中。从技术上讲，该项目将确定比目前已知的任何合金和工艺都更具成本效益和能效的合金和工艺。因此，该提案的广泛影响结合了优质结构材料可能的商业进步，以及参与该项目的本科生和研究生培训的广泛教育效益。技术摘要：这项工作将发展一类新的热力学稳定纳米结构材料的基础物理学，称为“纳米双相”合金，以及一种新发现的快速烧结机制，这种机制只能在这类纳米结构材料中诱导。由于这些合金在保持稳定的纳米级结构的同时表现出快速粉末固结的潜力，它们可能是成本低、节能、可扩展和广泛商业应用的大块纳米结构金属合成的关键。这些发现使得具有纳米级晶粒尺寸的纳米结构合金在不需要施加压力或电场的情况下，通过完整的高温固结循环保持稳定。就知识价值而言，该项目将探索这种新型纳米结构合金及其烧结机制。对W-Cr体系进行了系统的实验研究，探讨了合金成分、温度、杂质含量等工艺变量对致密化机理的影响。动力学参数如活化能和活化体积将被量化，并与观察到的微观结构演变进行比较。此外，一种新的动力学蒙特卡罗模拟方法将被开发、校准并应用于研究致密化机制，并确定界面和纳米级第二相在烧结中的独立作用。在项目的最后几年里，将探索更多的合金系统，以证明这种烧结机制更广泛地适用于适用于粉末路线生产的其他技术相关合金。就更广泛的影响而言，该提案结合了先进结构材料可能的商业进步，以及在培训本科生和研究生方面的广泛教育效益，包括新的烧结方法本身以及项目中使用的不同表征和建模方法。

Nontechnical AbstractFor decades, researchers have been pursuing so-called "nanocrystalline" alloys as next-generation materials. These materials have very finely controlled internal structures at the scale of just a few dozen atoms, and show dramatic improvements in strength, wear resistance, corrosion resistance, and many other functional properties. While laboratory work has succeeded in producing small samples of nanocrystalline material, this has not yet translated to commercial-scale production of "bulk" alloys, i.e., materials big enough to make engineering componentry from. This project is developing a scientific approach to solve the problem of scalability for these advanced materials. It explores the science of alloying in nanostructured powders that can be consolidated at high temperatures into bulk components, while still retaining the nanocrystalline structure. Scientifically, the project aims to develop a deep understanding of nanocrystalline alloy powders, their structure, and their processability. The project combines experimental and simulation-based tools, and focuses on a model alloy system based on the metal tungsten, used widely in cutting tools and machining equipment. Technologically, the project will identify alloys and processes that are significantly more cost-effective and energy-efficient than any known today. The broader impact of the proposal thus combines possible commercial advances in premium structural materials, with a wide range of educational benefits in the training of undergraduate and graduate students involved with the project. Technical AbstractThe proposed work will develop the fundamental physics of a new class of thermodynamically stabilized nanostructured materials, called "nano-duplex" alloys, as well as a newly discovered rapid sintering mechanism that can only be induced in this class of nanostructured materials. Because these alloys exhibit the potential for rapid powder consolidation while retaining a stable nanoscale structure, they may hold the key to cost- and energy-efficient, scalable, and broadly commercially applicable synthesis of bulk nanostructured metals. These discoveries enable nanostructured alloys with nanoscale grain sizes that are stable through a full high-temperature consolidation cycle to full density, without the need for applied pressures or fields. In terms of intelletucal merits, the project will explore this new class of nanostructured alloys and the mechanisms by which they sinter. A systematic experimental study is proposed on the W-Cr system, exploring the role of alloy composition, temperature, impurity content and other processing variables on the mechanisms of densification. Kinetic parameters such as activation energies and activation volumes will be quantified, and compared with observations of microstructure evolution. Additionally, a new kinetic Monte Carlo simulation approach will be developed, calibrated, and applied to study the mechanisms of densification and to identify the separate roles of interfaces and nano-scale second phases on sintering. In the out years of the project additional alloying systems will be explored to demonstrate the broader applicability of this sintering mechanism to other technologically relevant alloys that are amenable to powder route production. In terms of broader impacts, the proposal combines possible commercial advances in advanced structural materials, with a wide range of educational benefits in the training of undergraduate and graduate students on the new sintering method itself as well as on the different characterization and modeling methods that are used in the project.