Designing 2D nanostructured metals for age hardenability

非技术性防护根据定义，特殊材料将用于特殊应用，包括暴露于高温，因此超强金属的设计需要考虑极端条件下材料的强度。暴露于高温后，大块金属通常会变得机械柔软;这一规则的一个例外是设计用于时效硬化的材料。铝合金是时效硬化的经典实例，其中在加热之后，铝合金的强度由于杂质原子的局部重排而增加，这导致强化颗粒的内部纳米级网络。更强的材料在多个层面上造福社会;特别是它们使我们能够开发承载相同载荷的更轻结构（即更省油的汽车，更低的桥梁材料成本，或更高的航空航天应用性能）。 超强金属通常在金属内使用许多紧密间隔的纳米级颗粒来增加强度，但这些颗粒通常在暴露于高温时生长，并且它们的相对间距增加，这降低了强度。 在这项研究中提出了一种新的方法来加强金属，该方法依赖于形成交替的两种不同金属的层，从而产生具有许多内部界面的材料。 通过将强化颗粒限制在纳米级板中，最大颗粒生长将受到约束，并且在颗粒与颗粒间距增加的同时，界面与颗粒间距减小，导致保留的强度和热稳定性。 参与该项目的学生还将为中学科学教室设计课堂材料和配套的教案，以帮助教师为学生提供符合印第安纳州学习标准的引人入胜的活动，同时教授大学生如何有效地支持当地的教育推广。技术提示退火沉淀强化金属增加了第二相颗粒之间的间距，结构将软化。 通过在层内添加第二相沉淀物，退火将改变颗粒-颗粒和颗粒-界面间距。 本文将研究二维约束对亚稳Cr-Cu体系中Cr粒子析出的影响。 由于沉淀发生在FCC层内，具有沉淀物的纳米层压材料预期具有比单相层压材料更高的强度。 在退火过程中，颗粒之间的间距可能会增加，但颗粒与Cu-Cr界面之间的距离将随着沉淀物的生长而减小。 这提供了一种强化机制，该机制应导致退火后强度的增加，而不是退火后强度的降低，并且仅由于这些材料的二维结构才是可能的。 该系统还应耐过老化，增加3D架构中不可能的热稳定性水平。 然而，限制层滑移机制的强化依赖于位错核心的扩展和剪切FCC/BCC界面，它也必须确定，如果沉淀物在界面，而不是在层，加重或减弱强度增强。 该提案的目的是测试和验证可能的强化机制，确定平面系统的纳米级特征是否提供与其他硬化机制的添加剂协同强化（即，在2D受限系统中沉淀硬化、受限层滑移和固溶体硬化添加剂？），并为这种2D结构开发强化模型，该模型将预测新的金属多层合金结构的强度，该结构在退火时强化，并且在高温下比其他纳米特征金属表现出更小的强度下降。 这项工作的动机部分来自最近的分子动力学模拟，该模拟表明纳米层压强度随着沉淀物尺寸的增加而增加，为在高温下使用和/或经受传统上会降低其强度的热条件下使用的强化金属系统提供了新的方向。

Non-technical descriptionExceptional materials will, almost by definition, be used in exceptional applications, which can include exposure to elevated temperatures, and therefore the design of ultra-strong metals requires consideration of the strength of materials in extreme conditions. Bulk metals often become mechanically softer after exposure to high temperatures; one exception to this rule is materials that are designed to age harden. Aluminum alloys are the classical example of age hardening, where after heating the strength of the aluminum alloy increases due to local re-arrangements of impurity atoms that lead to an internal nanoscale network of strengthening particles. Stronger materials benefit society on several levels; in particular they allow us to develop lighter weight structures that carry the same loads (i.e. more fuel efficient cars, lower materials costs in bridges, or higher performance in aerospace applications). Ultra-strong metals often use many closely spaced nanoscale particles within the metal to increase strength, but often these particles grow upon exposure to high temperatures and their relative spacing increases, which decreases strength. A new method is proposed in this study to strengthen metals that relies upon forming layers of alternating two different metals which creates a material with many internal interfaces. By confining the strengthening particles to nanoscale slabs the maximum particle growth will be constrained, and at the same time that the particle-to-particle spacing increases the interface-to-particle spacing decreases, resulting in retained strength and thermal stability. The students working on this project will also design classroom materials and accompanying lesson plans for middle school science classrooms to help teachers provide students engaging activities that fulfill Indiana learning standards while teaching college students how to effectively support local educational outreach.Technical descriptionAnnealing precipitate-strengthened metals increases the spacing between second phase particles, and the structure will soften. By adding second phase precipitates within layers, annealing will change both the particle-particle and particle-interface spacing. This work will examine the effects of two dimensional confinement on precipitation of Cr particles within a metastable Cr-Cu system. As precipitation occurs within the FCC layer, the nanolaminates with precipitates are expected to have a higher strength than single phase laminates. During annealing the spacing between the particles may increase, but the distance between the particles and the Cu-Cr interfaces will decrease as the precipitates grow. This provides a strengthening mechanism that should lead to increases in strength after annealing, rather than decreasing strength after annealing, and is possible only due to the two dimensional architecture of these materials. The system should also be resistant to over-aging, adding a level of thermal stability not possible in 3D architectures. However, the confined layer slip mechanism of strengthening relies on dislocation core spreading and shear at the FCC/BCC interface; it must also be determined if precipitates at interfaces, rather than in the layer, accentuate or attenuate strength enhancements. The goal of this proposal is to test and verify the possible strengthening mechanisms, determine if the nanoscale features of planar systems provides additive synergistic strengthening with other hardening mechanisms (i.e. are precipitation hardening, confined layer slip, and solid solution hardening additive in 2D confined systems?), and develop strengthening models for this 2D architecture that will predict the strength of new metallic multilayer alloy structures that strengthen when annealed and exhibit smaller decreases in strength at elevated temperatures than other nano-featured metals. This work is motivated in part from recent molecular dynamics simulations that suggested nanolaminate strength increases as precipitate size increases, providing a new direction in strengthening metallic systems for use under elevated temperatures and or subjected to thermal conditions that would traditionally degrade their strength.