Pure Tungsten: Creep and Recrystallization of Pure and Dispersion Strengthened Tungsten
Tungsten and selected W-alloys are considered to be the primary candidates for armour and structural materials of ITER and of even more ambitious DEMO divertor designs. But even dispersion strengthened W alloys can recrystallize during DEMO relevant exposure times in the temperature range where the structural material of advanced divertors must operate (up to about 1300 °C).
A critical issue is the recrystallization of W-alloys and its interaction with aging time as well as elastic-plastic deformation during mechanical loading. To evaluate their applicability for the use as structural material, a special creep testing facility has been developed and implemented successfully. It allows for performing fully instrumented creep and creep rupture tests on selected reference W-alloys at typical temperatures of the divertor structural material. Pure tungsten and W-La2O3 (WL10) rods were used for specimen fabrication. Within the test program special emphasis has been laid on the effect of any interaction between recrystallization and long-term creep properties.
In addition aging tests and microstructural analysis of the materials as-delivered have been performed. These have shown that pure tungsten rod material shows starting recrystallization at 1100 °C after 200 hours whereas the La2O3 dispersion strengthened tungsten material remains stable. Further, if not recrystallized, tungsten shows a very high plasticity at 1100 °C that leads to necking of more than 90 %. At the same condition WL10 shows less ductility (necking of only 20 %) but increased creep strength by about 10-20 %. At 1300 °C, creep strength of pure tungsten drops dramatically due to severe recrystallization. First pores develop at grain triple points, and then cracks propagate along grain boundaries, which finally lead to inter-granular fractures.
COLLETED BY KAREN FROM www.chinatungsten.com
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