About | #IMR | Email

Dislocation-boundary interactions through in-situ TEM deformation of highly strained and twinned hcp metals.

Predictive models are needed for situations where experiments are impractical or impossible, such as the long-term aging of our nuclear reactors, or determining the reliability of our nuclear stockpile. Zirconium and its alloys are used in modern commercial light water reactors, and the safety of operation and lifetime of these reactors depends on the properties of the zirconium parts. Zirconium has therefore been the subject of many of these models, both because of its use in nuclear reactors, and because it is a nearly ideal representative of the hcp crystal structure. Because of the anisotropy of the hcp structure, there are generally not enough slip systems available to accommodate the imposed macroscopic deformation, and twinning can play a significant role. However, it has become increasingly obvious that short-range interactions and local mechanisms need to be included for the models to be predictive and physically-based. The goal of this proposal is to focus on the atomic to the microscopic length scale with a particular emphasis on identifying the controlling mechanisms of dislocation-twin boundary interactions as revealed through in situ deformation studies in the transmission electron microscope.

Electron tomography - 3D Tomographic reconstruction of dislocations and dislocation interactions

Electron micrographs capture the information on the electron exit surface of the sample and therefore provide only two-dimensional information. Of course, the interaction of dislocations with twins and hydrides occurs in three-dimensions. This loss of information makes it difficult to determine some interactions. I am exploring how to overcome this deficiency by using electron tomography methods to reconstruct a three dimensional image from a series of diffraction contrast images taken over a large angular range. Snapshots from different viewing angles of dislocations being ejected to accommodate the volume expansion associated with the formation of a hydride are shown below.



The upper series of images show the primary hydride, the ejected dislocation half loops and smaller hydrides in the surrounding matrix. Apparent from this series of images is the impact of too few images over too small an angular range - this is an example of the missing edge effect. The lower set shows the hydrides and attendant dislocations in schematic form. These images indicate the dislocations are coplanar and that some have impinged on the upper surface of the sample. The last image shows the superposition of the schematic on the original reconstructed image - the correlation is good. I am exploring using this combination of techniques to provide insight to the accommodation processes.






















PhD in Materials Science and Engineering


BS in Materials Science and Engineering, University of Illinois at Urbana-Champaign (2001)


Dislocation-boundary interactions through in-situ TEM deformation of highly strained and twinned hcp metals.

Electron tomography - 3D Tomographic reconstruction of dislocations and dislocation interactions

Nano-composite hard coating deformation (TiC)