Microstructure and impact properties of ultra-fine grained tungsten alloys dispersed with TiC

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

“…TiC exhibits a high melting point (³3520 K) and a self-adjustment capability of the lattice constant by forming a solid solution with W and leaving a non-stoichiometry of TiCx and offers strengthening effects of random grain boundaries due to precipitation of TiCx and its segregation at the grain boundaries: The occurrence of grain boundary precipitation always follows segregation of the constituents of TiC precipitate at grain boundaries. The strengthening effect by TiC addition was already reported in Mo bicrystals 13) and nanostructured Mo 1416) and confirmed in nanostructured W 17) with small amounts of TiC additions. Therefore, it is believed that the most preferable microstructure for mitigating embrittlement by recrystallization and radiation in W is composed of a high density of both TMC dispersoids and grain boundaries that are significantly strengthened by enrichment of the TMC components with negligibly small amounts of oxygen and nitrogen impurities.…”

“…10,17) Of importance is the use of high purity powders and thorough prevention of contamination with the interstitial elements of oxygen and nitrogen contained in the atmospheres through the whole fabrication process. For this, powder treatments are always made in a well degassed glove box filled with a purified Ar or H 2 gas.…”

“…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.…”

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

“…6,9) However, as the HIPing temperature was lowered, the relative density of the resultant as-HIPed compacts decreased; e.g., the relative density and the grain size of a compact HIPed at 1620 K for 5 hr were 93.9% and approximately 50 nm, respectively. 6,9) Therefore, fabrication methods of consolidated bodies have been attempted to be modified in order to achieve grain sizes less than 0.6 mm and relative density of around 99%. The key issue was to develop a method that allows sufficient outgassing from the MA treated powder during encapsulation of the powders in a metal can before HIP.…”

“…Such microstructural refinement can be achieved by materials processing based on powder metallurgical (P/M) methods including mechanical alloying (MA) 2) and hot isostatic pressing (HIP) under a controlled atmosphere with negligible amounts of oxygen and nitrogen. Therefore, the authors have been trying to establish a process for microstructural refinement in at first Mo, [3][4][5][6][7][8] and then W. 6,[9][10][11][12] They conducted mechanical alloying (MA) of powders of W, TiC or Ti and C, sintering of the MA treated powder by vacuum hot pressing (VHP) and hot isostatic pressing (HIP), followed by hot forging and hot rolling. The developed alloys exhibited improved ductility and high recrystallization temperature, but considerable difference was seen among the alloys.…”