Multiscale Computational and Experimental Analysis of Deformation Mechanisms in Amorphous-Crystalline Metallic Materials with Microstructure Complexity

Iowa State University, Ames IA

Investigators

Abstract

NON-TECHNICAL SUMMARY Enhancing the strength of a material is always at the expense of its ability to be purposely deformed or shaped, referred as ductility. Recently, inspired by biological materials, like nacre and dental enamel, a novel metallic composite which combines amorphous alloys (called metallic glass) with crystalline metals, such as copper or aluminum, is shown to have an appreciable strength improvement without sacrificing its ductility. However, up to date, the development of such materials is still at a 'trial and error' stage because: (i) the integration of metallic glass with crystalline metals leads to a complex material microstructure spanning a wide range of length scales from nanometers at the atomic scale to microns; (ii) many existing techniques, which either resolve the material as a collection of atoms or approximate it as a deformable body without considering its internal structure, are incapable to provide a full-scale interpretation on how such material responds to a mechanical forces like tension, compression, or shear. This project supports research addressing these problems through a combined computational and experimental analysis of the deformation in metallic composites over a range of length scales. This research will link the atomistic deformation physics with its overall mechanical performance. Two fundamental questions to be answered are: (a) how does the interface between the amorphous and crystalline phases contribute to their co-deformation? (b) how to architect the metallic composite microstructure such that its failure can be delayed? This research will advance the field by providing researchers with a platform that can be used in a rational design of high-performance materials for a variety of engineering applications such as biomedical implants, aircraft structures, and energy infrastructures. It will expose the next-generation workforce to a broad range of knowledge and skills related to mathematics, physics, mechanics, supercomputing, materials synthesis, processing, and characterization. Moreover, several kits of metallic composites will be developed for illustrating how little changes of the volume amounts of each phase in composites can significantly change its properties. These kits will be presented to science teachers at Gilbert middle and high schools in Iowa for promoting science and engineering to K-12 students. TECHNICAL SUMMARY In the search of strong and ductile metallic materials, one strategy is introducing interfaces, such as grain boundaries and twin boundaries, to resist dislocation motions. This strategy is usually accompanied by a decrease in ductility although it does lead to an enhancement in strength. By contrast, instead of blocking dislocations, the amorphous-crystalline metallic composites utilize the amorphous phases to absorb dislocations, and may fundamentally change 'the strength-ductility dilemma'. Nevertheless, a methodical engineering approach for developing such composites is not achieved so far due to a knowledge gap in correlating its multi-level microstructure with the overall mechanical performance. This project supports research to fill this gap. The mechanical behavior of amorphous-crystalline metallic composites with microstructure complexities will be analyzed from the atomistic to the microscale. Concurrent atomistic-continuum models that resemble the microstructure of the amorphous-crystalline metallic composite fabricated at the Department of Energy-Ames Laboratory will be developed. Multiscale simulations of plastic flow in such material will be conducted to gain the insight into the interplay between dislocations and shear transformation zones. The intrinsic difference in mechanisms for the deformation in magnetron sputtered orthotropic nano-laminates and ball-milled polycrystalline aggregates will be identified. This research opens up the possibility of architecting the metallic composites microstructure for a desired property. Many aspects of this research will not be limited to metals but are readily extendable to other classes of materials, such as biomimetic ceramics, metallic glass-based composites for electromechanical devices, corrosion-, and radiation-resistant materials for nuclear power plants. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.