Effect of grain refinement and twin structure on the strength and ductility of Inconel 625 alloy

The yield strength levels of solid-solution strengthened nickel-based superalloys are low compared to precipitation-strengthened counterparts. Here, Inconel 625 alloy was used as a model, thermo-mechanical treatments were employed to improve the yield strength of the alloys. Compared to the as-solution condition, the yield strength was increased from 291 to 676 MPa with the ductility reduced from 75 to 50% after cold rolling and annealing at 1073 K for 30 min. The strength-ductility synergy originates from (1) grain boundaries and pre-existing annealing twins act as strong barriers to hinder dislocations motion, and (2) the formation of deformation twins during plastic deformation provides an extra work-hardening region to maintain the excellent ductility. The strengthening effect of annealing twins is determined by the thickness rather than the length fraction. Deformation twins tend to form in the fine-grained Inconel 625 alloy (the grain size ranging from 3.1 to 4.7 mu m) during plastic deformation. This is the reason for an extra work hardening region in the hardening curve. Our present work can provide a reference for realizing the strength-ductility synergy of solid-solution strengthened nickel-based superalloys.

Automated summary

Thermo-mechanical treatments were employed to improve the yield strength of Inconel 625 alloy, leading to an increase in strength with a decrease in ductility. The strength-ductility synergy is achieved through the formation of grain boundaries, annealing twins, and deformation twins during plastic deformation.