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.