Structure and Texture of Oxide Dispersion Strengthened Alloy 617 for Very High Temperature Applications

High energy mechanically milled Alloy 617 ODS powder was consolidated by Spark Plasma Sintering (SPS) technique and subsequently annealed at 650 °C and 1050 °C (923 K and 1323 K). Microstructure and microtexture evolution during SPS and annealing have been investigated. SPS consolidated sample exhibited heterogeneous microstructure with ultra-fine grains surrounded by coarse grains. Inhomogeneous distribution of plastic deformation induced during ball milling resulted in heterogeneous nucleation and further grain growth during consolidation. The bimodal microstructure is advantageous with coarse grains providing ductility and fine grains providing strength by the Hall–Petch relationship. The bimodal grains structure was also retained during annealing. As-sintered specimen showed 〈100〉 texture parallel to the compression axis due to dynamic recrystallization during the SPS process. At 650 °C, annealed sample exhibited 〈111〉 annealing texture parallel to compression axis. The texture was randomized in sample annealed at 1050 °C. Precipitation analysis by SEM, XRD and TEM showed the presence of M23C6, M6C and Al2O3 in both As-sintered and annealed samples. Dispersoids analysis showed the presence of fine and uniform Y3Al5O12, Y4Al2O9 and a complex oxide rich in Ni, Y, Al and O. Stress–strain analysis from instrumented indentation test shows higher yield strength for Alloy 617 ODS in comparison with conventional Alloy 617.