| dc.description.abstract |
The mains objectives of this work were the elaboration and the study of hard films of
tantalum, deposited by electron beam evaporation, on steel substrates (XC100) containing about
1% weight of carbon. The specimens were vacuum annealed (10'" Torr) at various temperatures
in a range 450°C - 1100°C, and then characterized with X ray diffraction (XRD), Auger
Electron Spectroscopy (AES), X Ray Microanalysis. Scanning Electron Microscopy (SEM) and
Optic Microscopy (MM6).
We have shown that the adapted thermal annealing allows the diffusion of the carbon
atoms from the substrate towards the tantalum coating, and causes thereafter the transformation
of this last into tantalum carbide, the binary carbide Ta2C is formed the first about 600°C,
however at 900°C, the monocarbide TaC forms with the persistence of the binary carbide and
the formation of a small amount of the metastable phase zeta, whereas at 1 100°C it remains only
the monocarbide TaC, the others compounds being transformed
From a microstructural point of view, the obtained layers present lamellate grains with an
extremely small size that we can qualify them as nanocrystals No preferential orientation was
however observed
The heat treatment improves the structural state of tantalum films, because just after
deposition, they contain an important amount of structural defects and have a poor adhesion to
the substrate. |
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