Nanocrystalline tungsten-nickel heavy alloy reinforced by in-situ tungsten carbide: Mechanical alloying preparation and microstructural evolution

Mechanical alloying, as a low-temperature solid-state powder processing technique, was applied to prepare homogeneous nanocrystalline W-Ni heavy alloy reinforced by the in-situ formed WC, starting from the W-Ni-graphite elemental powders. The evolutions of constitution phases, microstructural features, and chemical compositions of the milled powders at various milling times were studied by the XRD, TEM, EDX, XPS, and laser particle size analyzer. The powder particles experienced a continuous refinement during 0-35 h milling, but had a tendency to coarsen with continued milling up to 45 h, due to the competitive operation between the mechanisms of fracturing and cold-welding. The alloying process including the solid dissolution of C and Ni in W and subsequent chemical composition homogenization was gradually completed after 35 h milling. The 35 h milled powder had a considerably refined particle morphology with a narrow size distribution (D-25=1.44 mu m, D-50=2.49 mu m, and D-90=5.31 mu m), leading to a significantly elevated specific surface area of 1462.56 m(2)/kg. The final product was identified as b.c.c. structured W alloyed with Ni, containing 1.07 at.% in-situ formed WC. The powders had a homogeneous nanocrystalline fine structure with a significantly decreased grain size below 20 nm. (C) 2012 Elsevier Ltd. All rights reserved.