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Application of isotropic graphite is important in wide range, especially
in semiconductor industry, aerospace rockets, high temperature gas cooled
reactors and first wall components of plasma-facing nuclear fusion devices.
This paper reports the experimental results of our studies on the thermal
shock resistance, which were evaluated via use of the Weibull distribution.
The thermal shock testing of the disk specimen undergone an induction coil
heating system was conducted. This isotropic graphite IG-11 (Toyo Tanso) is
used as the substrate in disk shape. Some disk specimen has been coated by
hot-filament CVD with a thin diamond film and diamond-like carbon film.
Weibull modulus somehow can show that the maximum stress in generally on the
surface. In our case, under the same condition of thermal shock testing,
the isotropic graphite with thin diamond has a value 4.6, in comparison with
that of a diamond-like carbon film has a value of 4.8 when the thickness is
2mm. When the thickness is 4mm, Weibull modulus of diamond film is 7.5 and
DLC film is 5.5.The thermal stress of diamond film is higher than the
graphite, which has the thickness of 4mm. It is better than DLC.
However, Weibull modulus of IG-11 disk specimens (4mm) shows its values of
drop between 8.4 and 8.9 according the different electrical powers. At the
same thickness, Weibull decrease with the electrical power increase. At the
same electrical power, the Weibull modulus increases first, then decreases
with specimen thickness.
The deposited thin film were analysis by Raman, XRD and SEM. The surface
morphology has affect to Weibull distribution very much. So, We can control
the deposition time and temperature, the morphology of film can change with
that. The ball-like morphology of diamond-like carbon will form the
tile-like morphology of diamond. So that, the concentration stress is
different with the surface morphology, and the Weibull modulus are
different, too.
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