Research

Amit Misra

Professor and Department Chair

amitmis@umich.edu

3062B H.H. Dow

T: (734) 763-2445

Bio

Publications

Group

Research


Nanomechanics and Metallic Interfaces Group

Our research program is focused on the fundamental understanding of the mechanical response of metallic alloys, composites and coatings through elucidation of deformation and fracture mechanisms via advanced transmission electron microscopy (TEM) and in situ nanomechanics characterization.

This mechanistic understanding is crucial to the development of predictive models of mechanical behavior of advanced metallic materials with ultra-high flow strengths without loss in ductility and toughness. In particular, we look to develop the scientific underpinnings of the design of next-generation structural materials that, for example, are high strength and yet light-weight, or achieve high strength without loss in electrical conductivity, or are high strength and tolerant to damage in extreme conditions of temperature, particle radiation or environment exposure.

 

Current research interests

 

Nanolaminate and Nanotwinned Metals

There is plenty of room at material interfaces! Nanolaminates are compositionally-modulated assemblies of two or more dissimilar materials that exhibit unprecedented properties due to nanoscale confinement and unique atomic arrangements at interphase boundaries. For example, Cu/Nb semi-coherent interfaces exhibit multiple atomic structures without any significant change in interface energy. These interface boundaries resist morphological evolution at elevated temperatures and are relatively weak in shear. The low shear strength leads to strong interactions with glide dislocations. The dislocation stress field causes localized shear of the interface and attraction of the dislocation into and core spreading along the interface plane. Dislocations with delocalized cores are strongly pinned in the interface leading to a high interface barrier for slip transmission and unusually high yield strengths. These interfaces are also effective sinks for point defects leading to attraction, absorption and annihilation of irradiation-induced vacancies and interstitials. Nanolaminates designed with such interfaces have resulted in ultra-high strengths without loss of plastic deformability, high thermo-mechanical stability and high resistance to radiation damage. Our group conducts research on a family of nanolaminate model systems synthesized by ‘bottom-up’ physical vapor deposition (e-beam evaporation or magnetron sputtering) or ‘top-down’ accumulative roll bonding approaches.

 

High Resolution TEM image of nanotwinned Cu
High-resolution TEM image of nanotwinned Cu

Nanotwinned metals are chemically homogeneous but crystallographically-modulated nano-confined structures resulting from profuse twin nucleation during film growth. Nanotwinning in metals such as Cu leads to ultra-high strengths while preserving the electrical conductivity since coherent twin boundaries are strong obstacles to glide dislocations due to geometric mismatch in slip systems but weak scattering sites for electrons.

 

 

 

 

 

 

 

 

Metallic Thin Films with Controlled Architectures

 

The goal of this project is to create nano-metallic materials that exhibit ultra-high strengths but by virtue of their bicontinuous, intertwined architecture, resist flow localization. We are using an iterative design process that integrates theory/computation, synthesis and structural characterization. Model material systems under investigation include co-sputtered Cu-Mo, Cu-Ag-Mo and Al-Si with bicontinuous intertwined morphology.

 

 

Nanoscale bicontinuous intertwined metallic composite: Cu(red)/Mo(green); individual ligament dimensions can be controlled from a few nanometers to a few tens of nanometers. 

Nanoscale bicontinuous intertwined metallic composite: Cu(red)/Mo(green); individual ligament dimensions can be controlled from a few nanometers to a few tens of nanometers.

 

Laser-processed Fine-scale Eutectic Composites

 

The goal of this project is to develop a fundamental understanding of plastic flow behavior in high-strength metallic composites containing disparate (soft/hard) phases. In particular, we seek to elucidate the role of the microstructural scale, morphology and interphase boundary structure and crystallography in enabling plastic co-deformability in composites containing relatively soft and hard phases in mono-, bi- or mixed-modal microstructures.

Model material systems under investigation include laser re-melted Al-based binary and higher-order eutectics. Laser processing enables nanoscale eutectic microstructures of varying morphologies and modalities.

 

Al-Al2Cu lamellar eutectic:As-cast (bottom): micro-scaleLaser-remelted (top): nano-scale

Al-Al2Cu lamellar eutectic: As-cast (bottom): micro-scale Laser-remelted (top): nano-scale

 

Dislocation-Interface Interactions

 

The need to develop predictive models of mechanical behavior that can accelerate the discovery, design and development of novel high-strength, light-weight Mg- and Al-based alloys requires quantitative, in situ straining TEM characterization. Our group uses state-of-the-art in situ nanomechanics in TEM to elucidate and quantify the mechanisms of dislocation interactions with key microstructural features such as precipitates, and grain and interphase boundaries. The vision is to couple atomic-scale imaging, in situ straining and quantitative stress measurement in the understanding of dislocation interactions to integrate with dislocation theory and simulations in developing predictive capability.

In situ nanoindentation in TEM

In situ nanoindentation in TEM 

 

Our research is sponsored by:

  • National Science Foundation-Designing Materials to Revolutionize and Engineer our Future (NSF-DMREF) program
  • Department of Energy, Office of Basic Energy Sciences (DOE-BES)
  • Light-weighting Innovations For Tomorrow (LIFT), a ManufacturingUSA Institute managed by Office of Naval Research
  • PRedictive Integrated Structural Materials Science (PRISMS), a DOE-BES Software Center for Predictive Theory and Modeling
  • Ford –UM Alliance
  • Modumetal, Inc.
  • Guardian Industries, Corp.

 

Current Collaborators:
  • Professors J. Mazumder, J.E. Allison, L. Qi, E. Kioupakis, University of Michigan
  • Professor J. Wang, University of Nebraska-Lincoln
  • Professor M.J. Demkowicz, Texas A&M University
  • Professors D. Farkas, W. T. Reynolds, M. Murayama, S.G. Corcoran, Virginia Tech
  • Dr. N.A. Mara, Dr. N. Li, Mr. J.K. Baldwin, CINT, Los Alamos National Lab, NM
  • Professor I.J. Beyerlein, University of California-Santa Barbara.