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Sprouster, D.

Publications and source records attributed to Sprouster, D..

18 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Proton irradiation effects in Molybdenum-Carbide-Graphite composites

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) has prompted the investigation of novel materials for beam-intercepting devices, and in particular for the collimators responsible for protecting the machine from beam losses. The HL-LHC collimation system will inevitably experience increased levels of radiation damage and undergo changes in their crucial physio-mechanical properties. Graphite-matrix composite materials containing molybdenum carbide particles, along with small amounts of titanium carbide, were developed with the objective of enhanced in-beam performance and tested under proton irradiation. The physical degradation observed in early grades of molybdenum carbide compounds, even after modest proton fluences, has prompted the development of advanced compounds. In this work, we examine the effects of proton irradiation on the microstructural and thermophysical properties of new grades of Molybdenum-carbide-graphite compounds up to fluences of ~2 × 10 20 p/cm 2 . Here, we employ a combination of precision dilatometry and high-energy X-ray diffraction to quantify the dimensional stability and crystallographic phase evolution both pre- and post-irradiation. Our results reveal that these new compounds exhibit superior resilience to radiation damage than their predecessors.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Radiation damage of a two-dimensional carbon fiber composite (CFC)

Carbon fiber composites (CFC) are, among other applications, already in use as low-impedance collimating elements for intercepting TeV-level protons machines, like the CERN Large Hadron Collider. Towards a comprehensive understanding of these materials’ properties and behavior, a series of radiation damage campaigns have been undertaken in order to quantitively investigate the response of AC-150 K CFC to high proton fluences. The CFCs dimensional changes, stability, micro-structural evolution, and structural integrity below and above 5 × 10 20 p/cm 2 fluence threshold were studied. The irradiating particles were protons of kinetic energies in the range of 130–200 MeV. The effects of the irradiation temperature (~90–180°C and 280–500°C) combined with the proton fluence on the dimensional stability and the microstructural evolution of this anisotropic two-dimensional composite structure were studied using precision dilatometry and X-ray diffraction. Our results shed light on the fluence-based limitations for these composite materials. Furthermore, we compare these results with reference unirradiated graphite, and we discuss the similarities and differences in the dimensional changes and post-irradiation annealing properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Hexagonal boron nitride (h-BN) irradiated with 140 MeV protons

Here, hexagonal boron nitride was irradiated with 140 MeV protons to a fluence of ~6 10 20 p/cm 2 at T irr ~200 °C. Isotropic graphite was also irradiated alongside h-BN under similar conditions and fluence to enable direct comparison of the two similar structures. The effects of proton irradiation on dimensional stability and microstructure were studied using precision dilatometry and energy dispersive Xray diffraction techniques revealing by direct comparison to graphite that h-BN can better resist radiation damage from bombardment when irradiated with protons impinging normal to the crystallographic planes or along the crystallographic c-axis. X-ray diffraction experiments also revealed a preferred orientation of the crystallites in bulk samples near the sample surface, an orientation influenced by irradiation. Thermal studies using differential scanning calorimetry and thermogravimetric analysis to 740 °C, augmented by precision dilatometry, provided evidence of subtle phase transitions attributed to residual w-BN in the matrix. Irradiation appears to induce shifting of such transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Fast Neutron Irradiation Embrittlement-ductilitization of an Iron-based Amorphous Alloy using In Situ Synchrotron X-ray Diffraction

Amorphous Fe-based nanostructured alloy coatings thermally sprayed on bcc steel substrate, were subjected to neutron irradiation doses up to 2 × 10 19 n/cm 2 . It is shown that the interplay between embrittlement and recovery of ductility is governed by amorphous to crystallization transition and phase decomposition in which temperature and irradiation dose have reciprocal effects. Microscopic (X-ray diffraction) observations on the behavior of the amorphous Fe-based alloy are correlated with relevant macroscopically observed mechanical behavior. It is shown that amorphous Fe-based alloy coatings maintain and even enhance their amorphous structure with irradiation, exhibit radiation-induced restoration of thermally-induced embrittlement and finally exhibit resistance to ductility loss up to the fluence of 2 × 10 18 n/cm 2 and good thermal stability up to 350 °C. The latter is deduced from X-ray diffraction experiments of in-situ tensile strain application on the irradiated coating.

36 MATERIALS SCIENCE↗