Microstructural development and its mechanism of mechanical alloyed nanocrystalline W-10Ni alloy reinforced with Y2O3 nanoparticles

The work presented here deals with the mechanical alloying (MA) preparation of W-10Ni matrix nanocomposites reinforced with nanometer-sized Y2O3 particles, using micrometer-scaled W, Ni (10 wt.%), and Y2O3 (2.5 wt.%) powder as the starting materials. The X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), and laser particle size analyzer were used to characterize the changes of constitutional phases, chemical compositions, and microstructural features of the nanocomposite powder during MA process. It revealed that after 10 h milling, the Ni element was found to diffuse into the W lattice continuously, leading to the formation of the W-Ni solid solution. The powder particles experienced a successive morphological change during milling, i.e., preliminarily refined (10 h)-significantly coarsened (20 h)-continuously refined (35 h)-slightly coarsened (45 h), due to the alternant predomination of the fracturing and cold welding mechanisms. The 35 h milled Y2O3/W-Ni nanocomposite powder had the most homogeneous and refined particle morphology, showing a narrow size distribution (D10 = 0.46 μm, D25 = 0.63 μm, D50 = 0.83 μm, D75 = 1.04 μm, and D90 = 1.24 μm) and a significantly elevated specific surface area of 3108.21 m2/kg. The average crystallite size of the W-Ni solid solution matrix of the 35 h milled nanocomposites was 12.5 nm and the mean size of Y2O3 reinforcing particles was less than 25 nm, exhibiting the typical nanostructures for both matrix and reinforcing phase. The spherical nanometer-sized Y2O3 reinforcing particles had the coherent interfacial structure with the W-Ni matrix. The underlying mechanisms for the phase change and microstructural evolution during MA of Y2O3/W-Ni nanocomposites were also proposed.