The modified Johnson-Cook strain-stress constitutive model according to the deformation behaviors of a Ni-W-Co-C alloy

The hardening or softening behaviors of the Ni-W based alloys, that can be applied in metal forming, high-speed impact, and penetration mechanics industries, are different from other traditional alloys under high strain rates (higher than 1000 s−1) or at high temperatures. The quasi-static and dynamic mechanical properties of a Ni-W-Co-C alloy, as well as the corresponding deformation behaviors and microstructure evolution, is studied herein. Further investigations and discussions on the constitutive relationships corresponding to dynamic deformations are carried out in this paper. The strain hardening behaviors are found varying with increasing temperatures, i.e., obvious enhancement of strength with increasing strains at 300–500 °C, but apparent softening behaviors at 700 °C. No dynamic softening behaviors are observed in the compressed specimens under high strain rates in range of 1000–3000 s−1, but with more very refined deformation twins under higher strain rates, suggesting the strain rate hardening effect may be enhanced. A feasible constitutive model is established by modifying the Johnson-Cook model, i.e., introducing a constant of λ′ to describe the variation of strength with the increasing temperatures and strains, providing a theoretical basis for the promising applications of this alloy.