Microstructural evolution and tensile properties of oxide dispersion strengthened Alloy 617 at elevated temperatures

摘要

This study investigated evolution of the microstructure of oxide dispersion strengthened Alloy 617 with annealing temperature. A mixture of prealloyed Alloy 617 and Y_2O_3 powders was mechanically alloyed and consolidated by hot-extrusion at 1100 ℃. Hot extrusion developed a submicron-sized grain structure with M_(23)C_6 carbides and finely dispersed Al_2O_3 and Y_2Ti_2O_7 oxides. The fine-grained structure was stable during subsequent annealing at temperatures up to 1250 ℃. Further increase of annealing temperature to 1300 ℃ resulted in a significantly coarsened grain structure, which was coincident with the abrupt coarsening of oxides. M_(23)C_6 carbides in the as-extruded conditions were transformed to M_7C_3 carbides with complex shapes when annealed at 1200 ℃, and their shapes changed to very coarse hexagonal prisms at 1250 ℃, which was followed by the formation of eutectic M_2C carbides at grain boundaries at 1300 ℃. Tensile tests of the as-extruded ODS Alloy 617 showed that the yield strength decreased steeply at a transition temperature of around 600 ℃, which can be attributed to diffusional creep along the grain boundaries.