High energy particle (neutron, proton and He ions) irradiation to materials
typically leads to deteriorating properties, including void swelling, blistering,
embrittlement, fracture and exfoliation of surfaces. This dissertation examines size
dependent radiation damage in nanostructured metallic multilayers synthesized by the
magnetron sputtering technique at room temperature. It reveals the roles of interface in
achieving enhanced radiation tolerance in metallic materials. The microstructure and
mechanical properties of as-deposited Cu/V multilayer films are systemically
investigated, providing the basis for studying radiation damage mechanisms.
Sputter-deposited Cu/V multilayers are subjected to helium (He) ion irradiation at
room temperature with a peak dose of 6 displacements per atom (dpa). The average
helium bubble density and lattice expansion induced by radiation decrease significantly
with decreasing h, where h is individual layer thickness. The magnitude of radiation
hardening decreases with decreasing h, and becomes negligible when h is 2.5 nm or
less. The interactions between interfaces and radiation induced point defects and the
evolution of microstructurs and mechanical behavior are discussed. This study indicates that nearly immiscible Cu/V interfaces spaced a few nm apart can effectively reduce the
concentration of radiation induced point defects.
Dose dependent radiation damage at room temperature in these Cu/V multilayers
is systematically investigated with a peak dose in the range of 1-12 dpa. Peak bubble
density increases with increasing dose, but it is much lower in Cu/V 2.5 nm multilayers
than that in Cu/V 50 nm specimens. A similar radiation hardening trend is observed in
multilayers irradiated at different fluences. Radiation hardening increases with dose and
seems to reach saturation at a peak dose of 6 dpa. Negligible hardening for fine ( h less than/equal to 2.5
nm) multilayers is observed at all dose levels.
Thermal stability of Cu/V multilayers is revealed by in situ annealing inside a
transmission electron microscope. During isothermal annealing at 600 degrees C grain boundary
grooving occurs across layer interfaces in Cu/V 50 nm specimens, whereas Cu/V 5 nm
multilayers appear rather stable. Annealing of Cu/V multilayers at 400 degrees C leads to
hardening of multilayers, whereas softening occurs in Cu/V multilayers annealed at 600
degrees C. The evolution of mechanical properties during annealing is correlated to the
degradation of the layer interface and the consequent reduction of interface resistance to
the transmission of single dislocation.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-08-7177 |
| Date | 2009 August 1900 |
| Creators | Fu, Engang |
| Contributors | Zhang, Xinghang |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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