Designing 2D nanostructured metals for age hardenability

非技术描述根据定义，例外材料将用于特殊应用，包括暴露在高温下，因此超强金属的设计需要考虑材料在极端条件下的强度。大宗金属在暴露在高温下后，通常会变得机械上变得更软；这一规则的一个例外是设计成时效硬化的材料。铝合金是时效硬化的经典例子，在加热后，由于杂质原子的局部重新排列导致内部纳米尺度的强化颗粒网络，铝合金的强度增加。更坚固的材料在几个层面上造福社会；特别是它们使我们能够开发出重量更轻、承载相同载荷的结构(例如，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)。超强金属通常使用金属中许多间隔很近的纳米颗粒来增加强度，但通常这些颗粒会在高温下生长，它们的相对间距增加，这会降低强度。在这项研究中提出了一种新的方法来强化金属，这种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板条中，最大颗粒长大将受到限制，同时颗粒与颗粒之间的间距增加，界面与颗粒之间的间距减小，从而保持强度和热稳定性。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参与性活动，同时教大学生如何有效地支持当地的教育外展。技术说明时效沉淀强化的金属增加了第二相粒子之间的间距，结构将变软。通过在层内添加第二相析出物，退火将改变颗粒-颗粒和颗粒-界面间距。这项工作将考察二维限制对亚稳态铬铜系统中铬粒子析出的影响。由于沉淀发生在fcc层内，含有沉淀的纳米层状物有望具有比单相层状物更高的强度。在退火过程中，随着析出物的增多，颗粒间距增大，但颗粒到铜铬界面的距离减小。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而可能。该系统还应该抵抗过老化，增加了3D建筑中不可能达到的热稳定性水平。然而，强化的约束层滑移机制依赖于fcc/bcc界面的位错核扩散和剪切；还必须确定是否在界面处析出，而不是在层中析出，从而加强或减弱强度增强。这项建议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与其他强化机制(即2D约束系统中的沉淀硬化、约束层滑移和固溶体强化添加？)提供相加协同强化，并开发这种2D结构的强化模型，该模型将预测新的金属多层合金结构的强度，这些结构在退火时强化，并且在高温下比其他纳米特征的金属表现出更小的强度下降。这项工作的部分动机是最近的分子动力学模拟表明，纳米层强度随着沉淀物尺寸的增加而增加，这为加强金属系统在高温和或受热条件下使用提供了新的方向，而热条件通常会降低金属系统的强度。

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.