Effect of Ambient and Cryogenic Milling on the Microstructure and Properties of Tungsten Matrix Composites Fabricated by Activated Sintering
Abstract
Tungsten matrix composites reinforced with TiB2
and Y2O3 particles were fabricated by milling under
ambient/cryogenic conditions and Ni activated sintering. Powder blends
constituting the W - 1 wt. % Ni - 2 wt. % TiB2 - 1 wt. % Y2O3
composition were mechanically milled for 12 h under ambient condition or cryomilled
for 10 min or sequentially milled under ambient and cryogenic conditions.
Milling was carried out in a high-energy ball mill under ambient condition
whereas cryogenic milling was conducted in externally circulated liquid
nitrogen. Milled powders were compacted using a hydraulic press and the pellets
were sintered at 1400°C for 1 h under Ar / H2 gas flowing
conditions. The effects of different milling types on the microstructural and
mechanical properties of the sintered composites were investigated. After
sintering, in addition to dominant W phase, small amounts of WB and NiW phases
were detected in all sintered samples. The application of cryomilling after
milling at ambient condition provided the disappearance of the clustered TiB2
and Y2O3 particles in the sintered sample: They were
located at the grain boundaries of W1Ni matrix and homogeneously distributed
through the microstructure. Sequentially milled and sintered composite had the
highest relative density (95.77 %) and the highest microhardness (7.23 GPa)
values among the samples. Nano-indentation tests showed that there was an
improvement in the hardness and elastic modulus of W matrix phase, which
yielded the values of 8.9 and 373.7 GPa, respectively.
Keywords
Tungsten matrix composites,Cryomilling,Activated sintering,TiB2,Y2O3
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