Study of the Ion‐Irradiation Behavior of Advanced SiC Fibers by Raman Spectroscopy and Transmission Electron Microscopy

Abstract

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.

On the limits of Reactive-Spark-Plasma Sintering to prepare magnetically enhanced nanostructured ceramics: the case of the CoFe2O4-NiO system

“…The powders were prepared by dispersing them in ethanol by sonication and depositing a drop of the resulting suspension on a copper TEM grid. The pellets were prepared by cutting thin foils using the Focused Ion Beam (FIB) technique according to a well-established procedure described elsewhere 50 . The foils were then deposited on a classical TEM grid for the observations.…”

Characterization of the ion-amorphization process and thermal annealing effects on third generation SiC fibers and 6H-SiC

“…Also, mean maximum and minimum Feret diameters -which correspond to the shortest and the longest distances between any two points along the grain boundary (GB) -were determined. These values yield, respectively, 26 and 36 nm for the HNS fibers and 141 and 210 nm for the TSA3 fibers [5]. at JANNUS-Orsay facility and to 2 Â 10 15 cm À2 at JANNUS-Saclay facility [8].…”

“…The specimens were extracted from the samples irradiated to 2Â 10 15 cm À2 using a Helios Nanolab 650 (FEI Co., Hillsboro, OR, USA) equipped with electron and Ga ion beams. The specimen preparation procedure is described elsewhere [5]. TEM observations were conducted in a conventional CM20 TWIN-FEI (Philips, Amsterdam, Netherlands) operated at 200kV equipped with a LaB6 crystal as electron source and a Gatan (Gatan Inc, Warrendale, PA, USA) heating specimen holder (25-1000°C) with manual temperature control.…”

On the first evidence of exchange-bias feature in magnetically contrasted consolidates made from CoFe2O4-CoO core-shell nanoparticles

“…It clearly evidenced that sizes of a few tens of nanometers were obtained for the involved spinel and rock-salt phases while sizes of some submicrometers were measured for the metal phases formed in situ . Transmission electron microscopy (TEM) observations performed on thinned ceramic pieces prepared by Focus Ion Beam (FIB) treatment 48 , give the same information. They showed a CFO-CO matrix with nanometer grain-size decorated with submicrometer size Co metallic precipitates (see Figure SI-5 in the supporting information section).…”