1. magnetic confinement - ENEA - Fusione

3. FUSION TECHNOLOGY 87
3.7 Materials
powder mixtures at >1430°C, but the results were not
satisfactory because of incomplete melting of the mixtures,
which led to inhomogeneities and defects. Thus, before the
brazing operations, the eutectic was prepared by melting a Si-
Ti mixture in an argon plasma furnace and then re-melting it
in an electron beam to get a fine eutectic structure. Powders
were prepared by milling the small ingots obtained and were
then used for the brazing experiments. First monolithic and
then SiC f /SiC composites samples were brazed.
Fig. 3.23 - Si-Ti brazed
joint micrography.
The joining was performed in both vacuum and inert
atmosphere. The joints had a very interesting morphology
(fig. 3.23). In particular, the joint layer showed:
• the absence of discontinuities and defects at the interface as
a result of complete melting of the powders;
• a fine eutectic structure with morphology comparable to that of the starting
powder.
Fig. 3.24 - Calculated
stress distribution in the
sample.
[3.42] C.A. Nannetti, et
al., Development of 2D
and 3D Hi Nicalon
fibres/SiC matrix
composites manufactured
by a combined CVI-PIP
route, presented at
ICFRM-10 (Baden Baden
2001), to appear in J.
Nucl. Mat.
A shear test performed at room temperature by means of a modification of the ASTM
D905-89 standard method gave remarkable results: the samples manufactured with
monolithic SiC cracked at high shear stress level, not in the brazing layer or at the
interface, but in the SiC bulk; while the composite samples exhibited up to 80 MPa
shear strength.
3.7.6 Measurement of residual stresses using neutron diffraction
techniques
In the framework of Underlying Technology, samples of high-heat-flux
components were tested in the ILL High Flux Reactor (Grenoble) to verify the
relevance of the
Residual Stress (MPa)
400
300
200
100
0
-100
-200
-300
-400
-500
Glidcop
5 10 15 20 25
Tungsten
Position (mm)
Long in-plane
Short in-plane
Normal
Interface
3.7.7 SiC/SiC ceramic composites as PFC material
compliance layer in the
stress evolution of the first
sample tested. Preliminary
results show that the
strains in Glidcop vanish
at about 300°C, indicating
a possibility to evaluate
the null strain temperature,
if the lattice is not
deformed by the
compliance layer. Figure
3.24 shows the calculated
stress distribution.
The campaign to manufacture composites with superior properties (Underlying
Technology activity) continued during 2001. In particular, the objective was to
evaluate the effect of densification by chemical vapour infiltration (CVI) and
polymeric infiltration and pyrolysis (PIP) on the thermal/mechanical properties of
Tyranno SA/SiC matrix composites and to compare the results with those of similar
3-D fibre textures of Hi-Nicalon/SiC matrix composites densified by CVI-PIP [3.42].
The fibre volumetric percentage ranged from 35 to 40% and the thickness was about
4 mm.