3D Interfaces Enhance Mechanical and Thermal Stability in Metallic Nanolaminated Composites
Justin Cheng, University of Minnesota
Although two-phase nanolaminates are known for high strength, they suffer from other shortcomings such as limited ductility and thermal stability at low layer thicknesses. Here, we show that broadening heterophase interfaces into “3D interfaces” as thick as the individual layers breaks offers a unique opportunity to tailor mechanical and thermal stability. In terms of mechanical behavior, we use micropillar compression and transmission electron microscopy to examine the processes underlying this breakthrough mechanical performance. The analysis shows that the 3D interfaces stifle flow instability via shear band formation through their interaction with dislocation pileups. To explain this observation, we use phase field dislocation dynamics (PFDD) simulations to study the interaction between a pileup and a 3D interface. Results show that when dislocation pileups fall below a characteristic size relative to the 3D interface thickness, transmission across interfaces becomes significantly frustrated. Our work demonstrates that 3D interfaces attenuate pileup-induced stress concentrations, preventing shear localization and offering an alternative way to enhanced mechanical performance. In terms of thermal properties, we show using bulk and In-situ TEM annealing that 3D interfaces increase thermal stability by preventing grain boundary grooving and subsequent layer pinch off. 3D interfaces are shown to possess thermally stable atomic configurations, providing diffusion barriers that delay the disruption of microstructure at high temperature in nanolaminates. Clearly, 3D interfaces provide a promising avenue forward towards interface-based property manipulation in nanocrystalline alloys that must survive extreme mechanical and thermal loads.
Abstract Author(s): Justin Y. Cheng, Shuozhi Xu, Zezhou Li, Youxing Chen, Jon K. Baldwin, Irene J. Beyerlein, Khalid Hattar, Nathan A. Mara