Microstructure and Bend Ductility of W-0.3 mass%TiC Alloys Fabricated by Advanced Powder-Metallurgical Processing

Abstract

Low temperature embrittlement, recrystallization embrittlement and radiation embrittlement in tungsten and its alloys are critical issues for use as high heat flux components and high-power density structural materials. In order to establish a process for microstructural control to improve the resistance to such embrittlement, modification of powder-metallurgical processing is proposed to avoid three microstructural factors giving detrimental effects on the ductility: (1) precipitation of the brittle W 2 C phase, (2) heterogeneity in grain size and particle distributions, and (3) loss of carbon which is a constituent of transition metal carbides. The processing was applied to fabricate W-0.3 mass%TiC alloys with a microstructure of fine grains and nano-sized dispersoids of TiC. Transmission electron microstructural observations and three-point bending tests at room temperature were performed on the alloys in the unirradiated state. It is demonstrated that the developed alloys are almost free from the three microstructural factors and exhibit appreciable room-temperature ductility before fracture in the as-forged and as-rolled states, but not in the as-HIPed state. This beneficial effect of plastic working on ductility improvement is strongly dependent on grain size and becomes prominent with decreasing grain size. Success in fabricating consolidated bodies with grain sizes as small as 0:17$0:4 mm and a high relative density of around 99% is presented.

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

“…The ultra-fine grains were, however, difficult to be maintained in the fully densified compacts after sintering because full densification requires high temperature sintering where significant grain growth would occur: When the MA treated W0.5%TiC powder was HIPed at 1620 K, the as-HIPed compacts contained porosity of as much as 6% although it still exhibited ultra-fine grains of 50 nm in diameter. 17) Fully densified, UFGR WTiC compacts were successfully fabricated in 2004: 19) HIPing at 16231673 K, approximately 2/5 of the melting point, resulted in precipitation of nano-sized dispersoids and essentially full densification without significantly increasing the grain size of the MA treated powder.…”

Superplasticity and high temperature deformation behaviour in nano grain Tungsten compacts

“…To improve such negative properties, various methods like the grain refinement, solid solution of Re, addition of dispersions or grain refinement by severe plastic deformation, have been used [1 -8]. The grain refinement of W enables to obtain both of superior sinterability [3,4] and excellent deformability at high temperature [4,5,6,9].…”

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

“…TiC is used as a reinforcement in W composites not only because of its very high melting temperature (3067 • C), high hardness, good high temperature strength, and good corrosion resistance [34], but also because of the formation of a (Ti,W)C solid solution, which has better mechanical properties than that of TiC, which can take place by means of substitution of some of Ti atoms with W in TiC lattice and improve mechanical properties of composites [25,[35][36][37][38]. W-TiC composites were first reported by Kitsunai et al [24] and were mainly investigated to date by several researchers [4,5,24,25,28]. However, there are no detailed studies about the sintering behaviour and microstructural properties of dispersion strengthened W-based composites sintered with the presence of a transition metal constituent.…”

“…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].…”

“…The mechanism of solid-state activated sintering is explained in regard to enhanced diffusion in nanoscale impurity-based, quasi-liquid, interfacial films in experiments and thermodynamic modeling studies [17][18][19][20][21][22][23]. The investigations about the activating sintering of W and usage of different refractory carbide, nitride and oxide phases such as TiC, TiN, ZrC, HfC, La 2 O 3 , Y 2 O 3 , HfO 2 , Sm 2 O 3 , and ThO 2 as dispersion strengtheners in W matrix composites were mainly investigated [2,[4][5][6][24][25][26][27][28][29][30][31][32][33]. TiC is used as a reinforcement in W composites not only because of its very high melting temperature (3067 • C), high hardness, good high temperature strength, and good corrosion resistance [34], but also because of the formation of a (Ti,W)C solid solution, which has better mechanical properties than that of TiC, which can take place by means of substitution of some of Ti atoms with W in TiC lattice and improve mechanical properties of composites [25,[35][36][37][38].…”