Microstructure evolution and mechanical properties of oxide dispersion strengthened Ni–Cr–Y₂O₃ alloys with novel powder production routes

We systematically investigated the microstructure and mechanical properties of oxide-dispersion-strengthened (ODS) Ni–Cr alloys prepared using Ni–Y₂O₃ powders via solution combustion synthesis (SCS) and alloying recomposition oxidation sintering (AROS) methods. Ni–4Y₂O₃ and Ni–40Y₂O₃ powders were successfully produced via SCS and AROS methods and added to Ni and Cr powders to produce Ni–20Cr–1.2Y₂O₃ powder mixtures. High-energy ball milling formed elongated Ni grains and Y₂O₃ phases with the successful mechanical alloying of Cr in both SCS and AROS powders. Subsequent spark plasma sintering (SPS) produced ultrafine Cr-depleted Ni grains owing to the formation of Cr₇C₃ and Cr₂O₃. Compared to the SCS method, the AROS method formed finer Y₂O₃ particles in both the milled powder and sintered alloy, leading to smaller Ni grain sizes owing to the improved grain boundary pinning. Importantly, the AROS-sintered alloy contains many coherent Y₂O₃ particles (with {100} and {111} facets and a cube-on-cube orientation relationship) formed in the Ni matrix by the oxidation reaction during the AROS process. The AROS alloy exhibited improved strength compared to the alloys fabricated by SCS and conventional mechanical alloying methods, mainly because of the increased strengthening from finer Y₂O₃ particles and Ni grains.