Microstructures and mechanical properties of a L12-structured precipitation strengthened Co-based superalloy

A L12-structured precipitation (γˊ) strengthened Co-based superalloy is identified based on thermodynamic calculation and experimental validation. An alloy with composition of Co9Al5Mo30Ni2Ta10Cr is fabricated to explore the relationships among processing, microstructures and mechanical properties. Typical γ/γˊ two-phase microstructures have been obtained after heat treatments, where the spherical γˊ phase with diameter of ∼ 100 nm are uniformly distributed in the face centered cubic (FCC) matrix. The L12 structured γʹ-(Ni, Co)3(Al, Ta) phase can be stabilized, which coherently precipitates in the FCC matrix (γ) during aging treatment. The alloy exhibits promising strength with comparison to traditional Co-based superalloys at a temperature range from room temperature (RT) to 1000 oC. The predominant deformation mechanism transits from shearing of dislocation pairs to dislocations bypassing γʹ phase when deformation temperature increases from RT to 1000 oC.