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ICFRM-12 Santa
Barbara, 4-9 December 2005
Abstract
Evaluation of the mechanical properties of W and W-1%La2O3 in view of divertor applications
Michael Rieth
Forschungszentrum
Karlsruhe, Institut für Materialforschung I, Karlsruhe, Germany
Within
an estimated operating temperature window of 800 °C to 1200 °C pure
tungsten and W-1%La2O3 (WL10) are currently envisaged for
use as structural materials in recent DEMO divertor designs. Here the upper
limit is mainly defined by recrystallization and loss of strength while the
lower temperature is limited due to embrittlement. For a qualified assessment
of these materials’ applicability, long-term creep and brittle-to-ductile
transition data – determined by standard tests – would be necessary. But up to
now such data have been unavailable.
Therefore,
creep rupture (up to 3000 hours) and standard impact tests have been performed
with specimens fabricated from commercial tungsten and WL10 rods. The specimens
were oriented parallel to rod axis for optimum mechanical properties and all
tests have been accompanied by detailed microstructure analysis with regard to
recrystallization and fracture mechanisms. Even so, ductile-to-brittle
transition temperatures of just 800±50 °C
for tungsten and approximately 950±50 °C
for WL10 have been determined. After 3000 hours at 1300 °C both materials
show also relatively low creep rupture strength (40 MPa for W and about 70 MPa
for WL10). While lower strength values could possibly be compensated by
according design modifications, embrittlement certainly can not. Furthermore, under
fusion specific neutron irradiation, an according alloy should exhibit
transition temperatures of 200-400 °C, at least, if utilized for divertor
components. Hence, the impact of these results on the use of dispersion
strengthened tungsten for divertor structures is discussed and alternative materials
as well as possible routes of alloy development are outlined.
249 words (250 words allowed)
Corresponding Author: Dr.
Michael Rieth
Forschungszentrum
Karlsruhe, IMF-I
Hermann-von-Helmholtz-Platz
1
76344
Eggenstein-Leopoldshafen, Germany
P.O.
Box 3640, 76021 Karlsruhe, Germany
Tel. +49 7247 82
2909, Fax +49 7247 82 4567
michael.rieth@imf.fzk.de