Type

Text

Type

Dissertation

Advisor

Trelewicz, Jason R. | Snead, Lance | Stach, Eric | Muntifering, Brittany | Hattar, Khalid.

Date

2017-08-01

Keywords

Materials science | radiation damage | tantalum | thermal stability | thin films | tungsten

Department

Department of Materials Science and Engineering.

Language

en_US

Source

This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree

Identifier

http://hdl.handle.net/11401/78331

Publisher

The Graduate School, Stony Brook University: Stony Brook, NY.

Format

application/pdf

Abstract

At the core of designing advanced materials for harsh environments involving high temperatures, extreme stresses, and aggressive irradiation conditions lies unprecedented thermal stability. Refractory metals are inherently suited for extreme temperature applications due to their high melting points, and recent focus has been placed on engineering nanocrystalline structures into these materials to enhance other key properties such as strength and radiation tolerance. Significant insights into the underlying mechanisms have been gained through advanced in situ transmission electron microscopy (TEM) techniques, which enable precise probing of nanoscale grain and defect structures under extreme conditions. First, amorphous tantalum films, deposited to a thickness of 20 nm, were in situ heat treated at temperatures over the range of 800-1200C to study the phases crystallized and their stability through devitrification. Quantitative image analysis of the electron diffraction patterns revealed a multiphase nanostructure composed of metastable tantalum films. These films, deposited to a thickness of 100 nm, were annealed in situ to characterize the stability of the nanostructure and grain growth up to 1200C. Examination of the bright-field images and diffraction patterns revealed limited grain growth at temperatures up to 40% of the melting point due to the presence of impurities at the grain boundaries. Finally, these techniques were applied in nanocrystalline tungsten thin films, 20 nm thick, to quantify grain growth behavior up to 1000C as a function of alloying state. Nominally pure nanocrystalline tungsten exhibited a bimodal grain growth succumbing to an equiaxed structure, while alloyed structures exhibited limited grain growth behavior attributed to compositional inhomogeneities such as grain boundary segregation. Self-ion irradiation, using 3 MeV W4+ ions, was employed to contrast damage states in unalloyed nanocrystalline tungsten relative to solute-stabilized tungsten alloys, from which design strategies were identified for enhancing their stability and radiation tolerance for nuclear engineering applications. | 213 pages

Download

Share

COinS