Radiation damage and thermal shock response of carbon-fiber-reinforced materials to intense high-energy proton beams

A comprehensive study on the effects of energetic protons on carbon-fiber composites and compounds under consideration for use as low-Z pion production targets in future high-power accelerators and low-impedance collimating elements for intercepting TeV-level protons at the Large Hadron Collider has been undertaken addressing two key areas, namely, thermal shock absorption and resistance to irradiation damage. Carbon-fiber composites of various fiber weaves have been widely used in aerospace industries due to their unique combination of high temperature stability, low density, and high strength. The performance of carbon-carbon composites and compounds under intense proton beams and long-term irradiation have been studied in a series of experiments and compared with the performance of graphite. The 24-GeV proton beam experiments confirmed the inherent ability of a 3D C/C fiber composite to withstand a thermal shock. A series of irradiation damage campaigns explored the response of different C/C structures as a function of the proton fluence and irradiating environment. Radiolytic oxidation resulting from the interaction of oxygen molecules, the result of beam-induced radiolysis encountered during some of the irradiation campaigns, with carbon atoms during irradiation with the presence of a water coolant emerged as a dominant contributor to the observed structural integrity loss at proton fluences $\ge 5\times {10}^{20}\mathrm{p}/{\mathrm{cm}}^2$. The carbon-fiber composites were shown to exhibit significant anisotropy in their dimensional stability driven by the fiber weave and the microstructural behavior of the fiber and carbon matrix accompanied by the presence of manufacturing porosity and defects. Carbon-fiber-reinforced molybdenum-graphite compounds (MoGRCF) selected for their impedance properties in the Large Hadron Collider beam collimation exhibited significant decrease in postirradiation load-displacement behavior even after low dose levels ($\sim 5\times {10}^{18}\mathrm{p}{\mathrm{cm}}^{-2}$). In addition, the studied MoGRCF compound grade suffered a high degree of structural degradation while being irradiated in a vacuum after a fluence $\sim 5\times {10}^{20}\mathrm{p}{\mathrm{cm}}^{-2}$. Finally, x-ray diffraction studies on irradiated C/C composites and a carbon-fiber-reinforced Mo-graphite compound revealed (a) low graphitization in the “as-received” 3D C/C and high graphitization in the MoGRCF compound, (b) irradiation-induced graphitization of the least crystallized phases in the carbon fibers of the 2D and 3D C/C composites, (c) increased interplanar distances along the $c$ axis of the graphite crystal with increasing fluence, and (d) coalescence of interstitial clusters after irradiation forming new crystalline planes between basal planes and excellent agreement with fast neutron irradiation effects.

Figure 1

SEM micrographs of 3D C/C composite and MoGRCF compound at room temperature.

Figure 2

SEM micrographs of MoGRCF (atomic fraction: 21.51% Mo and 78.485% carbon) with integrated C/C fibers following annealing at elevated temperatures ($a=400°\mathrm{C}$, $b=720°\mathrm{C}$, $c=965°\mathrm{C}$).

Figure 3

Setup of instrumented 3D C/C composite and ATJ graphite targets during the E951 24-GeV BNL AGS thermal shock experiments.

Figure 4

Comparison of 3D C/C and graphite response subjected to the same intensity proton pulse.

Figure 5

Modeling of the BLIP irradiation experiment (a) and actual array setup (b).

Figure 6

Numerical modeling of the proton interaction with an irradiation target array in tandem with the isotope production array downstream.

Figure 7

Layout of C/C composite specimens for proton beam irradiation. (a) 3D C/C with fibers at 45°, (b) 2D C/C (AC-150), (c) Ni foil placed in front of a 3D C/C array for postirradiation analysis of the proton beam position and shape, (d) 3D C/C with fibers in normal orientation in argon, and (e) MoGRCF in a vacuum.

Figure 8

Observed structural degradation in irradiated MoGRCF. (a) MoGRCF irradiated with $2.8\times {10}^{18}\mathrm{p}/{\mathrm{cm}}^2$ at 160 MeV followed by a fast neutron fluence of $3.2\times {10}^{18}\mathrm{n}/{\mathrm{cm}}^2$. (b) MoGRCF following irradiation at a peak fluence $\sim 1.1\times {10}^{21}\mathrm{p}/{\mathrm{cm}}^2$ with 160-MeV protons.

Figure 9

Photon spectra of the C/C composite (3D) irradiated at $6\times {10}^{21}\mathrm{p}/{\mathrm{cm}}^2$ in an argon atmosphere and direct contact with deionized cooling water.

Figure 10

Tensile tests on “dog-bone”-shaped 3D C/C proton-irradiated samples at $\sim 100°\mathrm{C}$ while directly cooled by ionized water. Shown in (a) is a direct comparison with unirradiated graphite. Slippage and premature failure at the sample head prevented the completion of the stress-strain curve (b). Test results, however, provided the basis for a radiation-induced change in the Young’s modulus as a function of the fluence.

Figure 11

Load-displacement results of 3D C/C composites irradiated in an argon atmosphere and in ionized cooling water at a fluence of $\sim 6\times {10}^{20}\mathrm{p}/{\mathrm{cm}}^2$.

Figure 12

Load and displacement for C/C composites and graphite. G-1273 and G-3273 indicate graphite heat-treated at 1273 and 3273 K, respectively. UD-2273 and UD-3073 represent C/C composites heat-treated at 2273 and 3073 K, respectively, whose fiber orientations are unidirectional. 2D-2273 and 2D-3073 indicate C/C composites heat-treated at 2273 and 3073 K, respectively, with 2D fiber orientations (after Nishida and Sueyoshi [4]).

Figure 13

Tension test of 3D C/C composite samples cut at 45° with a fiber “mesh” in the horizontal planes. The composite has $<10\%$ of the tensile strength in tension along the fibers, because it is controlled by the carbon-based fill between fibers. The effect of proton irradiation in increasing the Young’s modulus and strength is more pronounced than the one observed along the fibers (Fig. 10).

Figure 14

Four-point-bending test comparison of irradiated and unirradiated MoGRCF. Shown is the characteristic kinking appearing to shift upwards with irradiation. Also clearly depicted is the increase in the effective Young’s modulus (change of slope) following modest irradiation.

Figure 15

Thermal expansion coefficient of an unirradiated 2D C/C structure (Toyo-Tanso AC-150) along the two fiber orientations as a function of the temperature.

Figure 16

Preirradiation thermal cycle annealing of the 2D C/C structure (Toyo-Tanso AC-150) along the two fiber orientations.

Figure 17

Postirradiation thermal cycle annealing of the 2D C/C structure (Toyo-Tanso AC-150) along the two fiber orientations: normal to the fiber planes (left) and along the fibers (right). TC- ($200°\mathrm{C}$) and TC- ($300°\mathrm{C}$) indicate thermal cycles to peak temperatures $200°\mathrm{C}$ and $300°\mathrm{C}$, respectively.

Figure 18

Preirradiation thermal cycle annealing of the 3D C/C structure showing achieved dimensional stability after the third thermal cycle.

Figure 19

Thermal expansion coefficient of the proton-irradiated 3D C/C composite as a function of the average fluence. Two different samples irradiated at a similar fluence were tested and shown.

Figure 20

Postirradiation thermal annealing of irradiated 3D C/C to a high dose in an argon atmosphere.

Figure 21

Postirradiation thermal cycle annealing of proton-irradiated 3D C/C to a high dose comparing the effects of the irradiating environment (argon vs water).

Figure 22

Postirradiation thermal cycle annealing with an increasing cycle temperature ($300°\mathrm{C}$ vs $400°\mathrm{C}$) of proton-irradiated 3D C/C to a high dose.

Figure 23

Comparison of the dimensional change in unirradiated MoGRCF with IG-43, IG-430, and 2D C/C.

Figure 24

Postirradiation annealing of MoGRCF compared to graphite (left) and the dimensional change experienced by irradiated MoGRCF during a complete thermal cycle (right). Noted is the crossover during the cooling phase of the cycle.

Figure 25

D spacing and (002) diffraction peak of an unirradiated 3D C/C composite.

Figure 26

3D EDXRD phase map of as-received (left) and irradiated 3D C/C composite (right) to $6\times {10}^{20}\mathrm{p}/{\mathrm{cm}}^2$ in an argon atmosphere. Peak broadening and disordering are due to defect cluster formation.

Figure 27

Irradiation-induced interplanar change and graphitization (incomplete graphitization indicative by the knee on the LHS of the unirradiated curve) of fibers in the 3D C/C composite.

Figure 28

Irradiation-induced changes in the (002) and (112) diffraction peaks in 3D C/C compared to irradiated graphite with a similar proton fluence. Both graphite and 3D/C were irradiated in argon gas.

Figure 29

Irradiation-induced changes in the XRD spectra and d spacing of irradiated 3D C/C and 2D C/ composites irradiated to different proton fluences.

Figure 30

Comparison of the effects of fast neutrons on graphite as a function of the fluence [16] with the effects on graphite and 3D C/C composite structure by energetic proton irradiation in inert gas (argon).

Figure 31

Diffraction pattern of (a) unirradiated MoGRCF, (b) irradiated to a modest fluence [$\sim 6\times {10}^{18}(\mathrm{p}+\mathrm{n})/{\mathrm{cm}}^2$], and (c) irradiated graphite ($2\times {10}^{19}\mathrm{n}/{\mathrm{cm}}^2$), and (d) d spacing extracted from the diffraction patterns of the 2D area detector images [(a)–(c). One-quarter of the detector is shown in (a)–(c).

Figure 32

3D phase map of unirradiated MoGRCF generated using 200-keV polychromatic x rays via the EDXRD technique showing an uneven distribution of ${\mathrm{Mo}}_2\mathrm{C}$ phases from manufacturing of the compound.

Figure 33

Comparison of XRD spectra of unirradiated MoGRCF, 3D C/C, and graphite.

Figure 34

Irradiation-induced changes in MoGRCF observed via the EDXRD technique and 200-keV white x-ray beam: (a) scanning through a region of peak fluence $6\times {10}^{18}(\mathrm{p}+\mathrm{n})/{\mathrm{cm}}^2$, (b) evolution of phases in the compound, and (c) radiation-induced changes in the graphite phase (004) diffraction peak indicating crystal growth.