CAREER: Extreme Toughening of HCP Metallic Alloys via Nanospaced Stacking Faults

在微观层面上，镁、钛和钴属于一类具有六方结构的特殊金属。它们广泛应用的一个障碍是，基于六边形结构，无法设计出同时具有高强度和高成形性的材料；这些往往是相互排斥的。该学院早期职业发展(CAREAGE)奖支持的基础研究将发现和揭示在六角形结构中形成新的增韧特征的潜在机制，并使加工方法能够实现具有前所未有的强度和成形性的战略性金属材料。通过设计更坚固、更坚韧的金属合金，可以实现对开发车辆和交通系统至关重要的轻量化战略，以减少我们对化石燃料的依赖并减少污染。更重要的是，这些知识可以扩展到其他行业，如航空航天和医疗保健，从而促进进一步的技术进步和经济增长。这项研究将本质上是多学科的，并为加州大学河滨大学许多来自代表性不足群体的学生提供研究和教育机会。尽管平面边界(如纳米孪晶)显示出同时增强和保持具有体心立方和面中心立方晶体结构的纳米晶金属的延展性的能力，但它们在六边形紧密堆积材料中并不可行，因为随着颗粒尺寸的减小，孪晶难以孪生。文献线索和PI的初步观察表明，纳米间距的层错可以为六方紧密堆积材料提供协同增强和延展性，但还没有实验研究系统地研究这些材料形成这种特征的内在能力，以及导致它们形成、间距和密度的因素。因此，该奖项支持的研究目标是探索和揭示晶粒度、织构、层错能和变形条件对控制尺寸、间距和密度的断层形核和生长动力学的影响。接下来，将研究可实现的机械性能改善的幅度和机制。最后，将开发新的理论结构来解释在这些新材料中观察到的形成、强化和延展性。

Magnesium, titanium and cobalt are included in a particular class of metals with hexagonal structure at the microscopic level. A barrier to their widespread application has been the inability, based on the hexagonal structure, to design materials that have both high strength and high formability; these more often than not are mutually exclusive. The basic research supported in this Faculty Early Career Development (CAREER) award will discover and unravel the underlying mechanisms responsible for the formation of novel toughening features within the hexagonal structure, and enable processing methods to realize strategic metallic materials with unprecedented strength and formability. By engineering metallic alloys that are stronger and tougher, the lightweighting strategies critical for developing vehicles and transportation systems that reduce our dependency on fossil fuels and decrease pollution can be realized. More so, the knowledge can be extended to make advancements in other industries, such as aerospace and healthcare, thus promoting further technological advancement and economic growth. This research will be inherently multidisciplinary in nature and provide research and education opportunities for the many students from underrepresented groups at University of California Riverside.While planar boundaries such as nanotwins have shown the ability to concurrently strengthen and retain ductility in nanocrystalline metals with body center cubic and face center cubic crystal structures, they have not proven feasible in hexagonal close-packed materials based on the difficulty in twinning as the grain size decreases. Literature clues and preliminary observations by the PI have shown that nano-spaced stacking faults may afford synergistic strengthening and ductility for hexagonal close-packed materials, but there are no experimental studies that systematically investigate the intrinsic ability for these materials to form such features, nor the factors that lead to their formation, spacing and density. Thus, the objective of the research supported by this award is to explore and unravel the effects of grain size, texture, stacking fault energies and deformation conditions on the fault nucleation and growth kinetics that govern size, spacing and density. Next, the magnitude and mechanisms of mechanical property improvements achievable will be investigated. Lastly, new theoretical constructs will be developed to explain the formation, strengthening and ductility observed in these novel materials.