Microstructural stability of SiC and SiC/SiC composites under high temperature irradiation environment

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Abstract

Silicon carbide continuous fiber-reinforced silicon carbide matrix composites (SiC/SiC composite) are attractive as the structural material of advanced energy systems, including nuclear fusion. The irradiation may affect the fiber/matrix interphases which are responsible for the pseudo-ductile fracture behavior of SiC/SiC composites. In this work, the investigation of the microstructural evolution of SiC/SiC composites in a fusion environment is performed by the dual-ion irradiation method. Reinforcements were Tyranno™-SA and Hi-Nicalon™ Type-S. The displacement damage rate was up to 100 dpa. The irradiation temperature and He/dpa ratio were up to 1673 K and 60 appm, respectively. The microstructural modification induced by the dual-ion irradiation especially occurred in the interphase. The advanced SiC fiber did not shrink and the C/SiC multilayer interphase showed a superior microstructural stability against the dual-ion irradiation at high temperatures.

Introduction

Silicon carbide continuous fiber-reinforced silicon carbide matrix composites (SiC/SiC composites) have a lot of attractive properties, such as high strength, high chemical stability and low activation in thermo-nuclear applications. The low activation property makes SiC/SiC composites to be the most desirable material for the components of the advanced blanket system in fusion reactors [1].

Under an irradiation environment, the swelling and degradation of strength are the most essential mechanical and structural issues. The irradiation affects each constituent of the SiC/SiC composite and these effects are different for fiber, matrix and interphase. The recent development of SiC fiber reduces the oxide concentration and its composition and is close to stoichiometric SiC. These advanced SiC reinforcement has a crystallized microstructure. Due to the enhanced crystallinity the reinforcement behaves similar to the matrix in an irradiation environment. This is expected to keep the interphase stability and mechanical property of SiC/SiC composites [2].

The irradiation affects the carbon layer in the interphase. A most pronounced irradiation effect is the disorder of the graphitic structure. The irradiation increases the basal plane interspacing in the graphitic lattice and results in an anisotropic volume change. The improvement of the interphase structure is necessary to reduce this influence, so a C/SiC multilayer interphase structure is suggested for SiC/SiC composites [3].

The evaluation method for fusion materials is one of the important studies for materials development. A fusion reactor and a 14 MeV fast neutron source do not yet exist, so fission reactors are used for neutron irradiation experiments. The primary knock-on atom (PKA) energy and irradiation temperature in a fission reactor are different from those in a fusion reactor [4]. Especially in a fusion reactor, 14 MeV neutrons cause helium production from (n, α) nuclear reactions. The insoluble helium gas is considered to affect the irradiation induced displacement damage behavior [5]. For structural materials of the blanket system in a fusion reactor, SiC/SiC composites are exposed to high temperatures and heavy irradiation environments. The temperature and the neutron dose are estimated to be about 1273 K and up to 100 dpa, respectively [6].

For the evaluation of materials under this severe condition, the dual-ion irradiation method is suitable [7], [8]. The ion irradiation method has been studied for the simulation of 14 MeV fast neutron irradiation. An incident ion particle has enough PKA energy to induce a cascade damage similar to 14 MeV fast neutrons. In addition, the ion irradiation allows to modify the irradiation condition. Two different species are simultaneously irradiated to a material in a dual-ion irradiation. Heavy ions are used for inducing displacement damage and helium ions are implanted to play the part of produced helium by nuclear reactions under fusion conditions. The evaluation of helium production in SiC is almost impossible in a fission reactor, the dual-ion irradiation is more important to investigate its property in a fusion environment.

The objective of this work is to evaluate irradiation effects under near-fusion environment by the dual-ion irradiation and TEM observation on the microstructural stability of advanced SiC reinforced SiC composites [9], [10].

Section snippets

Experimental

The material used in this study are advanced SiC fiber-reinforced SiC composites. Reinforcements are Hi-Nicalon™ Type-S (Nippon Carbon Co.) and Tyranno-SA™ (Ube Industries Co.), which are near-stoichiometric SiC fibers with low oxygen and high crystallinity. The composites were produced by the chemical vapor infiltration (CVI) method. The interphases consists of a pyrolytic carbon (PyC) layer and a C/SiC multilayer, which is developed for fusion applications. The thickness of the PyC interphase

Results

The cross-sectional TEM micrographs of the carbon interphase in a dual-ion irradiated Tyranno-SA/PyC/CVD-SiC composite are shown in Fig. 1. Fig. 1(a) was taken near the surface and Fig. 1(b) is a dual-ion irradiated interphase. Fig. 1(c) shows the unirradiated interphase of the PyC layer. The irradiation direction is from the upper side of the micrograph. In Fig. 1(a), the fiber surface is flat to that of matrix; shrinkage of the fiber by irradiation induced crystallization does not occur and

Discussion

Tyranno-SA fiber is developed for fusion applications to guarantee microstructural stability under a heavy irradiation environment. This fiber almost behaves similar as the SiC matrix. The irradiation conditions of the present work have been established close to a fusion environment, in order to evaluate the effects after heavy irradiation in a fusion reactor. Advanced SiC fibers are promising candidates for the reinforcement for structural materials in a fusion reactor.

The interphase structure

Conclusion

Dual-ion irradiation studies have been performed for the advanced silicon carbide continuous fiber-reinforced silicon carbide matrix composite (SiC/SiC composite) for fusion application. The purpose of this work is to study the microstructural evolution of the interphase in a high-temperature, high-fluence irradiation and helium existence environment. The reinforcements were Tyranno-SA and Hi-Nicalon Type-S. The interphase structures were C/SiC multilayers and PyC layers. The irradiation

Acknowledgments

The dual-beam ion irradiation experiment was carried out with the assistance of H. Sakasegawa, K.-H. Park, S. Kondo, H. Suzuki, H. Ogiwara and Dr K. Jimbo, Institute of Advanced Energy, Kyoto University.

References (16)

  • P. Fenici et al.

    J. Nucl. Mater.

    (1998)
  • L.L. Snead et al.

    J. Nucl. Mater.

    (1998)
  • N. Sekimura et al.

    J. Nucl. Mater.

    (1994)
  • K. Ehrlich et al.

    J. Nucl. Mater.

    (2000)
  • Y. Katoh et al.

    J. Nucl. Mater.

    (2001)
  • S. Nogami et al.

    J. Nucl. Mater.

    (2000)
  • S. Pasquier et al.

    Compos. Appl. Sci. Manufact. Part A

    (1998)
  • R.J. Price

    J. Nucl. Mater.

    (1969)
There are more references available in the full text version of this article.

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