Collaborative Research: deformation mechanisms of fcc and hcp Cobalt with high-density stacking faults

非技术总结：薄膜形式的钴（Co）是一种重要的磁性材料，广泛应用于磁性数据存储设备、微机电和纳机电系统（MEMS/NEMS）以及环境友好的耐磨和耐腐蚀涂层。然而，钴薄膜的机械性能，无论是在面心立方（fcc）或六方密堆积（hcp）的形式知之甚少。主要研究者最近的研究表明，高密度堆垛层错（SF）-原子平面，破坏原子的有序排列-可以引入到fcc和hcp Co。这些SF可能会大大提高机械性能，导致更高的强度和延展性的Co。该项目的目的是阐明SF的密度的影响，并系统地研究与SF的Co的机械性能。调查人员有现有的合作，他们的专业知识很好地相互补充。该合作为学生提供了通过参与机构的相互访问，讲座和研讨会获得实验和模拟补充知识的机会。研究人员还安排研究生访问能源部-综合纳米技术中心，以获得先进的显微镜设施。从该项目中获得的知识可以纳入这两个机构的课程。合作研究者可以利用休斯顿大学成功的推广计划来扩大对工程的参与。主要研究者可以通过“博士课程途径”从少数民族机构招收一名少数民族研究生。两名研究人员不断监督本科生，并鼓励他们的学生参加重大会议。 技术总结：本项目的目的是研究具有高密度SF的fcc和hcp Co的变形机制。研究者将联合收割机实验和分子动力学模拟相结合，主要完成了以下工作：（1）研究面心立方（fcc）Co中SFs的成核和截断SFs的形成，并定制fcc和hcp Co中SFs的密度; 2）通过原位纳米压痕和原子模型相结合的方法，研究了面心立方Co的形变机制，包括位错-SF相互作用、尺寸效应和加工硬化;和3）研究了高密度SFs在hcp Co中的变形机制，并了解了hcp Co中形变孪晶的形核机制。金属力学行为中的应力场。此外，新的纳米力学测试工具与分子动力学模拟相结合，填补了知识空白，通过全面讯问的变形机制，在fcc和hcp钴与SFs在原子水平。

Nontechnical summary:Cobalt (Co), in the form of thin films, is a critical magnetic material with widespread applications in magnetic data storage devices, microelectromechanical and nanoelectromechanical systems (MEMS/NEMS), as well as environmentally benign wear and corrosion resistant coatings. Yet, the mechanical properties of Co films, either in face-centered-cubic (fcc) or hexagonal-close-packed (hcp) form are poorly understood. The principal investigator's recent studies show that high-density stacking faults (SFs) - atomic planes that disrupt the ordered arrangement of atoms - can be introduced into fcc and hcp Co. These SFs may drastically enhance mechanical properties leading to higher strength and ductility of Co. The aim of the project is to elucidate the effect of the density of SFs and systematically investigate the mechanical properties of Co with SFs. The investigators have existing collaborations and their expertise nicely complements each other. The collaboration provides students with the opportunity to gain complementary knowledge in experiments and simulations through mutual visits, lectures and seminars at the participating institutions. The investigators also have arrangement for graduate students to visit the Department of Energy - Center for Integrated Nanotechnologies to access advanced microscopy facilities. The knowledge derived from this project can be incorporated into curricula at both institutions. The co-investigator can leverage successful outreach programs at University of Houston to broaden participation in engineering. The principal investigator can recruit a minority graduate student through the "Pathway to Doctoral Program" from minority institutions. Both investigators continuously supervise undergraduate students and encourage their students to attend major conferences. Technical summary:The objective of this project is to investigate the deformation mechanisms in fcc and hcp Co with high-density SFs. The ultimate goal is to understand the significance of SFs in governing the mechanical properties of metals, and improving the strength and deformability of Co. The investigators combine experiments and molecular dynamics simulations to perform the following major tasks: (1) understand the nucleation of SFs and the formation of intercepted SFs in fcc Co, and tailor the density of SFs in fcc and hcp Co; 2) examine the deformation mechanisms in fcc Co, including dislocation-SF interactions, size effect and work hardening, via a combination of in situ nanoindentation and atomistic modeling; and 3) investigate the deformation mechanisms in hcp Co with high density SFs and understand nucleation mechanisms of deformation twins in hcp Co. This project could reveal the significant role of SFs in mechanical behavior of metals. Furthermore, the combination of novel nanomechanical testing tools with molecular dynamics simulations fills in the knowledge gap through comprehensive interrogation of the deformation mechanisms in fcc and hcp Co with SFs at the atomistic level.