Shear band localization in crystalline intermetallics
Abstract
When dislocation motion is energetically unfavorable in a polycrystalline material, typically such a material becomes brittle. Surprisingly, it has been recently demonstrated that certain intermetallics are able to deform plastically to a significant strain, in spite of the fact that they do not exhibit dislocation plasticity. Specifically, the finding was reported for SmCo5 and the underlying mechanism of plasticity was found to be the formation of thin amorphous shear bands inside the crystalline grains. In contrast to the amorphous shear bands observed in other materials, in SmCo5 shear bands form without the need for prior damage accumulation and they do not cause cavitation and fracture. Instead, these shear bands enable significant plastic strain in a material that otherwise would be brittle due to suppressed dislocation plasticity. The central hypothesis of this project is that amorphous shear bands in crystalline materials do not necessarily serve as precursors to fracture mechanisms, but instead act as carriers of enhanced plasticity, inhibiting crack initiation, and lead to improved toughness of the material. The goals of this project are to provide a fundamental understanding of when shear bands form in a crystalline material, when they act as mechanisms of ductility rather than as precursors to fracture, to develop a new mechanics theory that encompass these fundamental insights into a continuum-scale model of amorphous shear band evolution, and using this theory to predict the extent to which a materialÕs toughness can be increased through shear band plasticity. Toward these goals, we have formulated a number of scientific hypotheses that will be tested, using intermetallics as a testbed. The hypotheses will be also tested against selected examples of crystalline ceramics that form shear bands during high strain-rate deformation, but where the shear bands are known to nucleate cracks and to initiate brittle failure. An opportunity to advance the state of the art in this area comes from the aforementioned recent discoveries in intermetallics. In addition, the strength of this proposal is that it brings together PIs with expertise in materials modeling and experimental characterization, and in solid mechanics. Specifically, this proposal lays out an integrated approach that involves atomistic simulations of deformation, ex situ and in situ nanomechanical testing combined with high resolution transmission electron microscopy, and development of a new mechanics theory that will link the constitutive understanding of shear band mechanics with the underlying crystal structure and will in turn enable mechanical design and computational modeling at structural scales. Potential effects of the strain-rate will be tested by performing static and dynamic indentation experiments. Static indentation will be carried out using instrumented nanoindentation technique (strain rates on the order of 0.01 - 0.1 1/s). Dynamic indentation will be carried out using a recently developed laser-induced projectile impact (LIPIT) technique (strain rates 1,000,000 - 100,000,000 1/s). While the project is focused on intermetallics, the fundamental principles identified in this project are expected to be transferrable to other materials classes. We propose to change the traditional understanding of amorphous shear bands in crystalline materials from a bane to a boon; this is potentially transformative and could enable design and synthesis of new structural materials or engineering of existing materials to obtain superior toughness and resistance to fracture.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 25, 2021
- Source ID
- W911NF2110130
Entities
People
- Izabela Szlufarska
Organizations
- Army Contracting Command
- United States Army
- University of Wisconsin–Madison