Effect of Ambient and Cryogenic Milling on the Microstructure and Properties of Tungsten Matrix Composites Fabricated by Activated Sintering

Tungsten matrix composites reinforced with TiB 2 and Y 2 O 3 particles were fabricated by milling under ambient/cryogenic conditions and Ni activated sintering. Powder blends constituting the W - 1 wt. % Ni - 2 wt. % TiB 2 - 1 wt. % Y 2 O 3 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 / H 2 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 TiB 2 and Y 2 O 3 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