Mechanism and Stability of Deformation Twinning: Toward Predictive Understanding as a Function of Chemistry and Strain Rate
Abstract
Mechanism and Stability of Deformation Twinning: Toward Predictive Understanding as a Function of Chemistry and Strain RateFunds are provided to support the exploration of the nucleation and growth of deformation twins in materials.Technical POC: Dr. William M. Mullins, william.m.mullins@navy.milThis project addresses directly the PE 0601153N objectives for furthering basic research efforts including scientific study and experimentation directed toward increasing knowledge and understanding in national security related aspects of physical, engineering, environmental, and life sciences.Proposal AbstractDeformation twinning is a deformation mechanism that is activated as an alternative to dislocation slip and is important in a number of different classes of metals and metallic alloys. Of particular importance is characterizing the transition between dislocation slip and twinning, and quantifying the role each plays in accommodating strain. In FCC metals, a variety of models that incorporate the stacking fault energy, unstable stacking fault energy and twinning energy have been developed to explain the differences in the prevalence of twinning in particular material systems. A twinability parameter has been introduced in literature, which has been demonstrated erial order of the preference to twinning at conventional loading rates and temperatures. However, this model was developed for polycrystalline materials and does not predict the amount of twinning nor does it capture effects of strain rate or temperature. Moreover, this model also works solely for FCC metals and no similar models exist for BCC materials.This proposal presents a collaborative effort between the collaborators at Johns Hopkins University (lead), Colorado School of Mines, Colorado State University, and the University of California-Santa Barbara. This program will involve a combination of in situ and ex situ characterization at various length and time scales, coupled with multiscale simulation techniques, to be able to determine the exact mechanisms responsible for slip to twinning transitions moving from conventional to high strain rates in FCC and BCC metals and their alloys. Analysis at the micro and meso-scale of deformed samples for the two focus materials of this proposal, Cu and Ta (and their alloys) will be the main goal of this proposal. Statistical analyses of the high resolution, in situ, and 3D data sets will be carried out to identify twin formation with microstructural properties. The experimental results can be incorporated into the current modeling frameworks to reveal the stresses and energies involved in deformation twinning. From the knowledge gained, an advanced predictive capability will be built that introduces the formation and development of finite twin lamellae into a polycrystal model. The predictions will be compared with experimental data to validate model predictions of the stress-strain response of these two metals under a wide range of strain rates.The overarching goal of this proposal is to develop a predictive model for twin nucleation and evolution at various strain rates based on experimental inputs and validation. We will identify transitions between slip and twinning in various systems that will highlight the effect of local chemistry and crystal structure on dislocation activity, stability, and substructure formation by a combination of both experimental and theoretical/computational analysis from the mesoscale to the atomistic level. These data will translate to maps, or identifiers, for twin nucleation sites, and we will be able to build that all into an automated predictive code.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 31, 2020
- Source ID
- N000142012788
Entities
People
- Mitra L. Taheri
Organizations
- Johns Hopkins University
- Office of Naval Research
- United States Navy