Search

Raman spectroscopy is an efficient technique for studying the evolution of microstructure of materials under irradiation. For that purpose, a Raman spectrometer has been recently installed at the JANNUS-Saclay platform. In this paper, we describe the new setup for in situ experiments. These in situ experiments allowed following the microstructural evolution of different materials (SiC, ZrO2 and B4C) as a function of ion fluence on a single sample (either single crystal or polycrystalline ceramics) under the same irradiation conditions. Our results show that Raman spectroscopy is a versatile non-contact technique for studying on-line crystalline phase changes or amorphization of irradiated iono-covalent solids. A detailed analysis of Raman spectra is provided for the three materials (SiC, ZrO2 and B4C) investigated in this study, revealing quite different behaviors upon irradiation. Basically, Raman spectroscopy gives insight on these evolutions at the level of bonds given by specific phonon modes, in good agreement with Rutherford backscattering channeling (RBS/C), X-ray diffraction (XRD) or transmission electron microscopy (TEM) data, which provide information at a long-range scale. Copyright © 2015 John Wiley & Sons, Ltd.

6H–SiC single crystals and two types of SiC fibers, Hi-Nicalon type S and Tyranno SA3, have been irradiated with 4-MeV Au3+ up to 2 × 1015 cm−2 (4 dpa) at room temperature, 100°C and 200°C. These fibers are composed of highly faulted 3C–SiC grains and free intergranular C. Stacking fault linear density and grain size estimations yield, respectively, 0.29 nm−1 and 26–36 nm for the Hi-Nicalon type S fibers and 0.18 nm−1 and 141–210 nm for the Tyranno SA3 fibers. Both transmission electron microscopy and surface micro-Raman spectroscopy reveal the complete amorphization of all the samples when irradiated at room temperature and 100°C and a remaining crystallinity when irradiated at 200°C. The latter observations reveal a multi-band irradiated layer consisting in a partially amorphized band near the surface and an in-depth amorphous band. Also, nanocrystalline SiC grains with high stacking fault densities can be found embedded in amorphous SiC at the maximum damage zone of the Hi-Nicalon type S fibers irradiated at 200°C.

Hi Nicalon type S (HNS) SiC fiber and 6H-SiC single crystals have been irradiated with 4 MeV Au3+ at room temperature (RT) and to a fluence of 2 × 1015 cm−2. These irradiation conditions lead to the complete amorphization of the irradiated layer in both samples. Post-irradiation thermal annealing effect on the amorphized samples has been characterized in situ with both Environmental Scanning (E-SEM) and Transmission (TEM) Electron Microscopes. E-SEM observations reveal cracking and exfoliation of the amorphous layer in both samples for temperatures between 850 and 1000 °C. In parallel, TEM observations reveal recrystallization of the amorphous layer in both samples. Even though TEM thin foil specimens did not suffer mechanical failure during the tests, the good agreement between the recrystallization temperatures – 870 °C for the single crystal and 900 °C for the HNS fiber – place the recrystallization process as the stress source for the cracking and exfoliation phenomena. Crack detail of a Hi Nicalon type S SiC fiber triggered by the post-irradiation thermal annealing.