Development of Irradiation hardening of Unalloyed and ODS molybdenum during neurtron irradiation to low doses at 300C and 600C
Unalloyed molybdenum and Oxide Dispersion Strengthened (ODS) molybdenum were irradiated at 300 C and 600 C in the high flux isotope reactor (HFIR) to neutron fluences of 0.2, 2.1, and 24.3 x 10{sup 24} n/m{sup 2} (E > 0.1 MeV), producing damage levels of 0.01, 0.1 and 1.3 Mo-dpa. Hardness measurements, electrical resistivity measurements, tensile testing, and Transmission Electron Microscopy (TEM) were used to assess the defect structure. Irradiation hardening was evident even at a damage level of 0.01 dpa resulting in a significant increase in yield stress, decrease in ductility, and elevation of the Ductile-to-Brittle Transition Temperature (DBTT). The observed size and number density of voids and loops as well as the measured irradiation hardening and electrical resistivity were found to increase sub-linearly with fluence over the range of exposure investigated. This supports the idea that the formation of the extended defects that produce irradiation hardening in molybdenum are the result of a nucleation and growth process rather than the formation of sessile defects directly from the displacement damage cascades. The formation of sessile defect clusters in the displacement cascade would be expected to result in a linear fluence dependence for the number density of defects followed by saturation at fluences less than 1-dpa. This conclusion is supported by Molecular Dynamics (MD) simulations of cascade damage which do not reveal large clusters forming directly as a result of the short-term collapse of the cascade. The finer grain size for the unalloyed Mo and ODS Mo compared to Low Carbon Arc Cast molybdenum results in slightly less irradiation hardening and slightly lower DBTT values. The unalloyed molybdenum used in this work had a low impurity interstitial content that correlates with a slightly lower void size and void number density, less irradiation hardening and lower change in electrical resistivity in this fluence range than is observed for ODS Mo. Although the differences are relatively subtle, this result does suggest that high purity can result in slightly improved resistance to irradiation embrittlement in molybdenum at low fluences.
- Research Organization:
- Bettis Atomic Power Laboratory (BAPL), West Mifflin, PA; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC11-98PN38206
- OSTI ID:
- 920290
- Report Number(s):
- B-T-3624; TRN: US0805331
- Resource Relation:
- Conference: Annual Meeting of the Minerals, Metals, and Materials Society, New Orleans, LA, 03-10-2008
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CARBON
DEFECTS
DUCTILITY
ELECTRIC CONDUCTIVITY
EMBRITTLEMENT
GRAIN SIZE
HARDENING
HARDNESS
HFIR REACTOR
INTERSTITIALS
IRRADIATION
MOLYBDENUM
NEUTRON FLUENCE
NEUTRONS
NUCLEATION
OXIDES
TRANSITION TEMPERATURE
TRANSMISSION ELECTRON MICROSCOPY
Molybdenum
Irradiation Effects
Microstructure