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

镁、钛和钴是一类特殊的金属，在微观层面上具有六边形结构。它们广泛应用的一个障碍是无法基于六角形结构设计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（Career）奖支持的基础研究将发现并揭示六边形结构中形成新型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强度和可成形性的战略金属材料。通过设计更坚固、更坚韧的金属合金，轻量化战略对开发车辆和运输系统至关重要，从而减少我们对化石燃料的依赖，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。这项研究本质上是多学科的，并为加州大学河滨分校许多来自代表性不足群体的学生提供研究和教育机会。虽然平面边界（如纳米孪晶）在具有体中心立方和面中心立方晶体结构的纳米晶金属中显示出同时增强和保持延展性的能力，但由于晶粒尺寸减小而难以孪晶，它们在六角形密排材料中并不可行。文献线索和PI的初步观察表明，纳米间距层错可以为六边形密排材料提供协同强化和延展性，但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，也没有导致其形成，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尺寸、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进的幅度和机制。最后，将发展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.