Development of Nanostructured W and Mo Materials

Abstract

This paper presents the current status of the development of nanostructured refractory transition metals of W and Mo, with emphasis on the effects of nano-structures upon the mitigation of embrittlement by high ductile-to-brittle transition temperature (low temperature embrittlement) and by irradiation (radiation embrittlement) that is the key issue of the materials for use in extreme environments. An overview of processing of nano-structured refractory metals with and without dispersoids is given. The features of microstructures of the refractory metals are described in connection with grain growth behavior due to very high internal energy of nano-structures. Effects of nanostructures on physical and mechanical properties and radiation performance with neutron and light ions such as 3MeV He 4+ and 1keV H 3+ are presented. It is shown that grain boundaries are not only effective sinks for irradiation-induced point defects, but also are distributors of implanted light ions by enhanced diffusion in nano-structured refractory metals.

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

“…(2) Irradiation with 1 keV H3 containing ~0.8% C did not cause (a) 8 significant blistering but produced small holes on the surface, probably by ejection of grains [32]. (3) The thermal conductivity of W-0.5TiC is considerably lower than that of pure W. The thermal conductivity of W and UFG W-TiC become closer at high temperatures [33,34]. (4) Thermal shock loading under ELM (edge localized modes) conditions as they will happen within the International Thermonuclear Experimental Reactor (ITER) caused cracking in network-like patterns with a maximum depth of 170 µm [34] A new microstructural modification method was developed to strengthen the GBs in the recrystallized state, adjust the grain size and remove the residual pores.…”

Development of Nanostructured Tungsten Based Materials Resistant to Recrystallization and/or Radiation Induced Embrittlement

“…(1) Grains: 23,25,29) TEM (Transmission Electron Microscopy) observations show that the UFGR WTiC exhibits equiaxed grains in the recrystallized state. TiC addition, even with 0.25 mass%, has a significant effect of grain refinement.…”

“…3.2 Mechanical properties 23,29,30) The yield and fracture strengths and the ductile brittle transition temperature (DBTT) defined as the nil ductility temperature, were measured by three-point bending tests. The fracture strength was estimated to be the maximum fiber stress given by…”

Microstructural characterizations of Ni activated sintered W–2wt% TiC composites produced via mechanical alloying

“…However, it is very difficult to fabricate tungsten because of its high melting point and low ductilitiy [1,3]. In recent years, utilizing powder metallurgy and advanced sintering techniques such as hot isostatic pressing (HIP), fabrication of fully dense W composites has become possible at much lower temperatures (∼1350 • C) than the melting point of W [4][5][6].…”