Towards self-healing metals by employing optimally-dispersed Ti-Ni shape memorynano-particles

尽管自修复的概念对所有类型的材料和应用都很有趣，但迄今为止，材料设计的成功案例主要限于聚合物系统，少数情况下是陶瓷。金属材料中的自愈合-尽管金属在结构应用中起主导作用-是研究最少的，这是由于将常规（聚合物）愈合概念应用于金属的明显困难。金属体内部的缓慢化学反应和室温下的缓慢扩散速率需要专门为金属材料设计新的自修复机制。NanoTiNi在自修复金属材料领域提出了一个新的概念，可能会开辟材料设计的新时代。其主要思想是将形状记忆效应封装在纳米分散的相干颗粒中，这些颗粒将充当提供金属自主自愈的自愈剂。将共格形状记忆纳米颗粒引入标准固溶体金属基体中并通过其稳定。连贯的主体基质将表现出标准的机械性能，例如强度、延展性和断裂韧性。通过优化形状记忆纳米颗粒的尺寸和分布，将产生特殊和新颖的自修复特性，例如保证对纳米裂纹的最佳长期抵抗力，在正常情况下，纳米裂纹将触发断裂的发生。为了本发明的目的，纳米裂纹和它们的应力/应变场将充当局部应力源，激活纳米颗粒的转变，从而激活自修复过程。NanoTiNi的想法是由最近的原子模拟，清楚地表明，应力驱动的晶界能够愈合接近纳米裂纹的动机。然而，由于应力驱动的晶界是缓慢的，并且需要外部应力来激活，因此它不容易成为自修复机制。因此，在我们的方法中，我们用马氏体相变过程中基体纳米颗粒界面的边界运动代替晶界运动。这使得该机制局部化和自主化，从而成为真正的自我修复机制。鉴于所提出的目标具有高度挑战性，NanoTiNi提供了一种综合方法，将最先进的有限温度从头计算模拟和原位多尺度实验表征技术与长期存在的合金设计知识相结合。为了使该项目在资助期内可行，NanoTiNi专注于特定的材料系统Ti-Ni-V，Ti-Ni作为纳米颗粒的形状记忆合金。应调查该模型系统的机制，但是，开发的方法和知识将适用于其他材料具有类似的转换性能。

Although the concept of self-healing is interesting for all classes of materials and applications, the material design success stories are so far mainly limited to polymeric systems, and for a few cases to ceramics. Self-healing in metallic materials--despite the leading role of metals in structural applications--is the least investigated, due to the obvious difficulty of the application of conventional (polymeric) healing concepts to metals. Sluggish chemical reactions inside the metallic bulk and slow diffusion rates at room temperatures necessitate novel self-healing mechanisms to be designed specifically for metallic materials. NanoTiNi proposes a novel concept within the field of self-healing metallic materials that might open the way to a new era in materials design. The main idea is to encapsulate the shape memory effect in nano-dispersive coherent particles which shall act as self-healing agents providing autonomous self-healing of metals. The coherent shape memory nano-particles will be introduced into and stabilized by a standard solid solution metallic matrix. The coherent host matrix will exhibit standard mechanical properties such as strength, ductility, and fracture toughness. The special and novel self-healing properties will arise by optimizing the size and distribution of the shape-memory nano-particles such as to guarantee an optimum long-term resistance to nano-cracks which--in normal circumstances--would trigger the onset of fracture. For the present purposes, nano-cracks and their stress/strain fields will act as local stress sources activating the transformation of the nano-particles and thereby the self-healing process. The NanoTiNi idea is motivated by recent atomistic simulations which clearly reveal that a stress-driven grain boundary was able to heal an approaching nano-crack. Since however a stress-driven grain boundary is slow and needs an external stress to be activated, it does not readily qualify as a self-healing mechanism. In our approach we therefore substitute the grain boundary motion by the boundary motion of the matrix nano-particle interface during the martensitic transformation. This renders the mechanism localized and autonomic and thus a true self-healing mechanism. Given the highly challenging nature of the proposed goals, NanoTiNi provides an integrated approach combining state of the art finite temperature ab initio simulations and in situ multiscale experimental characterization techniques in conjunction with long standing alloy design knowhow. To render the project feasible within the funding period, NanoTiNi focuses on a specific material system, Ti-Ni-V, with Ti-Ni as the shape memory alloy for the nano-particles. The mechanisms shall be investigated for this model system, however, the developed methodology and knowledge will apply to other materials given similar transformation properties.