EAGER: Controlling Microstructure for Strong and Damage Tolerant Nanocrystalline Metals

纳米晶体金属和合金（晶粒尺寸小于~100 nm的多晶体）为结构应用提供了一系列吸引人的机械性能，包括高强度和硬度、增强的抗疲劳性和摩擦学鲁棒性。这些优点来自于大部分材料存在于相邻晶体之间的界面处，称为晶界。对于这些材料，这种高比例的界面体积可能会导致有害的影响，如热不稳定性和相对较差的损伤容限。 纳米晶金属的许多当前和未来应用，例如坚固的涂层、电气互连、微米和纳米机电系统以及软磁体，都会使这些材料受到极端的机械胁迫，这可以激活微观结构转变并改变有益的材料性能。EARLY概念探索性研究资助（EAGER）奖支持以纳米晶合金中晶界化学的控制可用于定制纳米晶材料在极端服务环境中抵抗晶界迁移的热稳定性和机械稳定性为中心的研究。控制这种行为可以允许前所未有的控制损伤容限，从而使一种新颖的和廉价的结构材料的设计strategy.In这项研究计划中，研究人员的目标是控制纳米晶合金的晶界化学作为一种手段来编码的热和机械驱动的晶界迁移在服务条件下的开始。在遇到极端机械环境的情况下（例如，在应力集中处，如裂纹尖端），可以触发应力驱动的晶界迁移以响应损伤，从而赋予材料损伤容限。这种动态材料响应基于局部应力触发，该局部应力触发驱动微观结构转变并耗散能量以减轻灾难性失效，从而实现强度和韧性。该研究将通过以下科学和技术目标来完成：（a）识别和表征导致机械诱导的晶界迁移和晶粒生长的机制，（B）识别和表征这些机制受晶界化学影响的方式，（c）识别将偏析到晶界并调节热和应力驱动的晶界迁移的元素，（d）合成具有定制晶界化学的纳米晶合金，以及（e）进行材料表征和定量原位机械测试。

Nanocrystalline metals and alloys (polycrystals with grain sizes less than ~100 nm) offer a suite of appealing mechanical properties for structural applications, including high strength and hardness, enhanced fatigue resistance, and tribological robustness. These virtues derive from the large fraction of material that resides at the interfaces between neighboring crystals, known as grain boundaries. For these materials, this high fraction of interfacial volume can cause deleterious effects such as thermal instability and relatively poor damage tolerance. Many present and future applications of nanocrystalline metals such as robust coatings, electrical interconnects, micro- and nano-electro-mechanical systems, and soft magnets subject these materials to extreme mechanical duress, which can activate microstructural transformation and alter the beneficial materials properties. This EArly-concept Grant for Exploratory Research (EAGER) award supports research centered on the concept that control of grain boundary chemistry in nanocrystalline alloys can be used to tailor the thermal and mechanical stability of nanocrystalline materials against grain boundary migration in extreme service environments. Control over this behavior can allow for unprecedented control of damage tolerance, thus enabling a novel and inexpensive structural materials design strategy.In this research program, the investigators aim to control grain boundary chemistry in nanocrystalline alloys as a means to encode the onset of thermally- and mechanically-driven grain boundary migration under service conditions. In cases where extreme mechanical environments are encountered (e.g. at stress concentrations such as crack tips), stress-driven grain boundary migration can be triggered to respond to damage, endowing the material with damage tolerance. This dynamic material response is predicated on local stress triggers that drive microstructure transition and dissipate energy to mitigate catastrophic failure, allowing for both strength and toughness. The research will be accomplished via the following scientific and technical goals: (a) identify and characterize the mechanisms that lead to mechanically-induced grain boundary migration and grain growth, (b) identify and characterize the manner in which these mechanisms are influenced by grain boundary chemistry, (c) identify elements that will segregate to grain boundary and modulate thermal and stress-driven grain boundary migration, (d) synthesize nanocrystalline alloys with tailored grain boundary chemistry, and (e) perform material characterization and quantitative in situ mechanical testing.