Microstructure and mechanical properties of Ni–Cr–Y₂O₃ alloy sintered powder composed of oxide-embedded metallic particles

In this study, oxide (Y₂O₃)-embedded Ni particles were fabricated via a new process. The process involves the mechanical hydrogenation of Ni–Y alloy into Ni–YH₂ and the selective oxidation of Ni–YH₂ to Ni–Y₂O₃. The alloy powders were prepared for sintering by the mechanical alloying of a mixed powder. The powder was prepared with a desired composition (Ni–20wt.%Cr–1.2wt.%Y₂O₃) by adding Ni and Cr powders to the Ni–Y₂O₃ composite prepared by the new process. For comparison, a mixed powder with the same composite was prepared using a conventional mechanical alloying (MA) approach. Samples of the two powders were sintered by SPS at 850, 900, 950, and 1,000 ^oC. The relative densities of all samples were higher than 99.7% at all sintering temperatures. The oxide particles and matrix grain sizes of the Ni–20Cr–1.2Y₂O₃ alloy prepared by this new process were finer than those in alloys fabricated by conventional MA processes. Therefore, the improvement in the mechanical properties of the Ni–20Cr–1.2Y₂O₃ alloy prepared by the new process was attributed to the refinement of the oxide particles.