Recent progress in R&D on tungsten alloys for divertor structural and plasma facing materials

Abstract

Tungsten materials are candidates for plasma-facing components for the International Thermonuclear Experimental Reactor and the DEMOnstration power plant because of their superior thermophysical properties. Because these materials are not common structural materials like steels, knowledge and strategies to improve the properties are still under development. These strategies discussed here, include new alloying approaches and microstructural stabilization by oxide dispersion strengthened as well as TiC stabilized tungsten based materials. The fracture behavior is improved by using tungsten laminated and tungsten wire reinforced materials. Material development is accompanied by neutron irradiation campaigns. Self-passivation, which is essential in case of loss-of-coolant accidents for plasma facing materials, can be achieved by certain amounts of chromium and titanium. Furthermore, modeling and computer simulation on the influence of alloying elements and heat loading and helium bombardment will be presented.

Fabrication, microstructure and mechanical properties of W NiTi composites

“…While for samples of WeNi 42 Ti 53 Nb 5 and WeNi 44 Ti 56 composites, they were composed of only nearly equiatomic NiTi matrix and W particles. When the Ti: Ni ratio raised to 58: 42, small amount of Ti 2 Ni remained in NiTi matrix, as seen from Fig. 3(d).…”

“…However, the major disadvantage of tungsten is its ceramic-like brittle behavior and poor workability at room temperature, which restrict its structural applications [2]. To answer this challenge, the concept of developing composite microstructures by combining tungsten with ductile phases has been developed, through which an improvement in ductility at room temperature has been obtained in several kinds of tungsten based composites [3e5], especially for the well-known two-phase tungsten heavy alloys [6e9].…”

“…A little variation in the ratio of the two elements might result in a large difference in the transformation temperatures and can lead to the formation of brittle intermetallics [28e31]. For Ti-rich alloys (around 50 at% Ni), stable Ti 2 Ni appears in NiTi alloy due to little solubility for Ti in excess of 50 at.% [28]. While for Ni-rich alloys, precipitation proceeds through a series of phases: Ti 3 Ni 4 /Ti 2 Ni 3 until finally the stable Ni 3 Ti phase is reached [28,29].…”

Evaluation of defect formation in helium irradiated Y2O3 doped W-Ti alloys by positron annihilation and nanoindentation

“…Tungsten and tungsten alloys are currently considered promising candidates for plasma facing components in future fusion reactors, in particular for the divertor and first wall components [1]. As a high-Z material, tungsten has a low sputtering erosion rate, a high thermal conductivity, high mechanical strength and a high melting temperature.…”

“…Titanium has limited solubility in W, so that only small contents of Ti up to 10 wt.% are reported in the literature [2][3][4][5] and the melting temperature remains close to that of pure tungsten. Ti addition also alters the core structure of screw dislocations and their slip mechanism and thus increases the W ductility [1]. Y2O3 nanoparticles inhibit grain growth, strengthen the matrix and enhance oxidation resistance [2].…”