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Parish, Chad M

Publications and source records attributed to Parish, Chad M.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Advanced Characterization of Fuel Pellet and Cladding from the HB Robinson NPP

In order to predict the behavior and response of materials to extreme environments of a nuclear reactor, comprehensive models have been developed over the past several decades. These models are typically validated against carefully designed single or double variable experiments which may be systematically altered in order build up a model of behavior under the conditions being examined. In reality, this does not necessarily compare well with the real application situations whereby the behavior of the material under irradiation is determined by multiple variables changing simultaneously e.g. temperature, irradiation flux and fluence, and pressure. This is particularly so when considering the highly dynamic environment of a fuel assembly within a nuclear power plant (NPP) core. This work aims to provide near-atomic resolution microstructural and chemical data of a fuel/clad specimen that has been used in service within a commercial NPP. Atom probe tomography and S/TEM characterization of the cladding showed the presence of small scale clusters containing Fe and Cr, along with segregation of these minor solutes to dislocations. SEM examination of the fuel pellet showed relatively large fission gas bubbles that had burst due to the metallographic polishing process to prepare the sample for examination. SEM-EDX mapping revealed the presence of Xr bubbles located beneath the surface that still retained their Xe concentration. Metallic precipitates were also observed. S/TEM-EDX of the fuel material also revealed the presence of small metallic precipitates. In addition, small Xe bubbles were also found to be present in the material, lying along grain boundaries only. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Alignment of Iron Nanoparticles in a Magnetic Field Due to Shape Anisotropy

During high magnetic field processing there is evidence for alignment of non-spherical metallic particles above the Curie temperature in alloys with negligible magneto-crystalline anisotropy. The main driving force for alignment is the magnetic shape anisotropy. Current understanding of the phenomenon is not adequate to quantify the effect of particle size, aspect ratio, temperature and the magnetic field on particle alignment. We demonstrate a Monte Carlo approach coupled with size scaling to show the conditions under which alignment is possible.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Nano-twin Mediated Plasticity in Carbon-containing FeNiCoCrMn High Entropy Alloys

Equiatomic FeNiCoCrMn alloy has been reported to exhibit promising strength and ductility at cryogenic temperature and deformation mediated by nano-twining appeared to be one of the main reasons. We use the FeNiCoCrMn alloy as a base alloy to seek further improvement of its mechanical properties by alloying additional elements, i.e., interstitial carbon. Moreover, the effects of carbon on microstructures, mechanical properties and twinning activities were investigated in two different temperatures (77 and 293 K). With addition of 0.5 at% C, the high entropy alloy still remains entirely single phase face-centered cubic (FCC) crystal structure. We found that these materials can be cold rolled and recrystallized to produce a microstructure with equiaxed grains. Both strain hardening rate and strength are enhanced while high uniform elongations to fracture (~70% at 77 K and ~40% at 293 K) are still maintained. The increased strain hardening and strength could be caused by the promptness of deformation twinning in C-containing high entropy alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Response of nanostructured ferritic alloys to high-dose heavy ion irradiation

A latest-generation aberration-corrected scanning/transmission electron microscope (STEM) is used to study heavy-ion-irradiated nanostructured ferritic alloys (NFAs). Results are presented for STEM X-ray mapping of NFA 14YWT irradiated with 10 MeV Pt to 16 or 160 dpa at -100°C and 750°C, as well as pre-irradiation reference material. Irradiation at -100°C results in ballistic destruction of the beneficial microstructural features present in the pre-irradiated reference material, such as Ti-Y-O nanoclusters (NCs) and grain boundary (GB) segregation. Irradiation at 750°C retains these beneficial features, but indicates some coarsening of the NCs, diffusion of Al to the NCs, and a reduction of the Cr-W GB segregation (or solute excess) content. Ion irradiation combined with the latest-generation STEM hardware allows for rapid screening of fusion candidate materials and improved understanding of irradiation-induced microstructural changes in NFAs.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2014

Microstructure and Sn crystal orientation evolution in Sn-3.5Ag lead-free solders in high temperature packaging applications

Understanding the reliability of eutectic Sn-3.5Ag lead-free solders in high temperature packaging applications is of significant interest in power electronics for the next generation electric grid. Large area (2.5mm 2.5mm) Sn-3.5Ag solder joints between silicon dies and direct bonded copper substrates were thermally cycled between 5 C and 200 C. Sn crystal orientation and microstructure evolution during thermal cycling were characterized by electron backscatter diffraction (EBSD) in scanning electron microscope (SEM). Comparisons are made between observed initial texture and microstructure and its evolution during thermal cycling. Gradual lattice rotation and grain boundary misorientation evolution suggested the continuous recrystallization mechanism. Recrystallization behavior was correlated with dislocation slip activities.

high temperature packaging↗
DOE OSTI2014

Effect of tungsten crystallographic orientation on He-ion-induced surface morphology changes

In order to study the early stages of nanofuzz growth in fusion-plasma-facing tungsten, mirror-polished high-purity tungsten was exposed to 80 eV helium at 1130 C to a fluence of 4 1024 He/m2. The previously smooth surface shows morphology changes, and grains form one of four qualitatively different morphologies: smooth, wavy, pyramidal, or terraced/wide waves. Combining high-resolution scanning electron microscopy (SEM) observations to determine the morphology of each grain with quantitative measurement of the grain's orientation via electron backscatter diffraction (EBSD) in SEM shows that the normal-direction crystallographic orientation of the underlying grain controls the growth morphology. Specifically, near-<001> || normal direction (ND) grains formed pyramids, near-<114> to <112> || ND grains formed wavy and stepped structures, and near-<103> || ND grains remained smooth. Comparisons to control specimens indicate no changes to underlying bulk crystallographic texture, and the effects are attributed to surface energy anisotropy, although, surprisingly, the expected {101} low-energy planes were not the most stable. Future developments to control tungsten texture via thermomechanical processing, ideally obtaining a sharp near- <103> || ND processing texture, may delay the formation of nanofuzz.

Parish, Chad M↗