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21XV International Symposium on Self-Propagating High-Temperature Synthesis
SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS AND SPARK PLASMA SINTERING OF TUNGSTEN ALLOYS FOR FUSION APPLICATIONS
S. Dine*", E. Bernard*, C. Grisolia*, N. Herlinc, and D. Vrel"
aLSPM, UPR 3407 CNRS, Villetaneuse, 93430 France bCEA, IRFM, Saint Paul lez Durance, 13108 France cCEA, IRAMIS, Gif-sur-Yvette Cedex, 91191 France. *e-mail: sarah.dine@lspm.cnrs.fr
DOI: 10.24411/9999-0014A-2019-10031
Since tungsten has been chosen as the reference material for the ITER divertor, extensive research has been conducted in order to improve some key properties for whose pure, commercial grade tungsten, present some limitations. Among these, one can find mechanical properties at room temperature, where the brittleness of tungsten reduces its machinability, but also resistance to blistering linked to hydrogen implantation [1], and to corrosion at high temperatures.
Recent studies have shown that low grain sizes, under 700 nm could induce a sharp decrease of the ductile to brittle transition temperature (DBTT), down to cryogenic temperatures [2]; it is also believed that nanostructured bulk tungsten, with an enhanced grain boundaries network would also be favourable to back-diffusion of implanted hydrogen atoms. On the other hand, chromium and vanadium alloying elements are believed to improve corrosion resistance (as in stainless steels) and to limit grain growth during heat treatments.
However, current production routes are not suitable for the fabrication of large bulk nanostructured tungsten samples.
In this work, we propose a novel methodology based on self-propagating high-temperature synthesis (SHS) to obtain partially alloyed nanometric powders in the 20-150 nm range (Fig. 1) [3]. These powders were then sintered by spark plasma sintering (SPS), and mechanical tests were performed. Our SHS reactor is able to synthesize up to 500 g of powder in a reproducible way.
m
001 101
I 20 um I
Fig. 1. SEM image of tungsten powders Fig. 2. EBSD mapping giving the developed by SHS reactor. crystallographic orientation of the grains on
the sample W-2000°C-5'.
ISHS 2019 Moscow, Russia
Results obtained from SEM, EDX, EBSD and XRD observations on sintered samples show that full tungsten densification may be obtained at a temperature lower than 1800°C and that the resulting morphology, keeping a partial nanostructure inherited from the synthesized powders (Fig. 2), seems indeed favorable to the use of these materials in fusion environments. Hardness measurements were performed and show a systematic increase proportional to the amount of alloying element. Compressive tests show also a significant increase in elastic limit, up to 1 GPa, depending on the nature and the amount of alloying elements (up to 6 wt %). Nevertheless, our samples are not brittle and show a plastic deformation of up to 40% before fracture.
1. K. Ouaras, M. Redolfi, D. Vrel, C. Quiros, G. Lombardi, X. Bonnin, K. Hassouni, J. Fusion Energ, 2018, vol. 37, pp. 37-46.
2. A.A.N. Nemeth, J. Reiser, D.E.J. Armstrong, M. Rieth, Int. J. Refract. Met. Hard Mater., 2015, vol. 50, pp. 9-15.
3. S. Dine, E. Bernard, N.H. Boime, C. Grisolia, D. Tingaud, D. Vrel, SHS synthesis and SPS densification of nanometric tungsten, Adv. Eng. Mate., 2018, 1701138.
