s Effect of Carbon Addition on the Property of Mechanically Alloyed Ni-Y2O3

We synthesized Y2O3-reinforced nickel-matrix nanocomposites by mechanical alloying of Ni-Y2O3, Ni-Y, Ni-NiO-Y and Ni- CuO-Y powders. Mechanical alloying of constituent powder mixtures resulted in a complete dissolution of yttrium or Y2O3 in nickel, forming a nickel-based solid solution. However, undesirable oxides such as NiO easily formed after a prolonged milling and subsequent sintering even in an inert gas atmosphere. The oxidation occurred almost inevitably due to oxygen impurity which remained at the surface of starting powders and in an inert gas used for milling or sintering. To solve this problem, we added a small amount of carbon or polyethylene as process control agents during ball milling. The result showed that the addition of these carbon-based additives, in particular polyethylene, was very effective to reduce a harmful formation of over-grown oxides during annealing and sintering, while promoting the oxidation of yttrium to form fine and uniformly distributed Y2O3 from the nickel-based solid solution.