Temperature effects on deformation substructures and mechanisms of a Ni-based single crystal superalloy

Abstract

Mechanical behaviors of a Ni-based single crystal superalloy have been investigated by tensile testing at various temperatures. Deformation substructures and mechanisms have been systemically revealed from micrometer to atomic scales by using advanced scanning electron and scanning transmission electron microscopes. Results show that deformation mode of the alloy strongly depends on the temperature due to competitive responses of the γ and γ′ phases under mechanical loading and their original stress statuses. At temperatures from ambient to 750 °C, plasticity is governed by dislocation shearing in both phases, where slip modes of γ are <110>{111} and those of γ′ are <112>{111}, <110>{111} and <110>{001}. At moderate temperatures (850 °C ≤ T ≤ 900 °C), plasticity mainly involves microscopically uniform deformation of both phases. The matrix deforms first so that channels parallel to tensile direction are narrowed due to the Poisson's effect, after that deformation of γ′ follows. The active slip modes are <110>{111} for γ, <112>{111}, <110>{111}, <110>{001}, and <001>{001} for γ′. At temperature higher than 1000 °C, plastic strain is also derived from deformation of both phases, but deformation of the matrix plays critical roles, due to relatively weak strength of this phase. The operative slip modes are <110>{111} for γ, but mainly <110>{001} and <001>{001} for γ′. Our results clearly provide a comprehensive and multiscale (from micrometer to atomic) understanding on the deformation mechanism of Ni-based superalloys, which can be critically beneficial and offer mechanistic guidelines to design new/next generation superalloys.