The strain rate effect on strength behavior of CoCrNi medium entropy alloy up to 106 s−1

Abstract

It is of great scientific significance and application value to reveal and understand the multi-scale mechanical properties and deformation mechanisms of medium entropy alloys (MEAs) under wide strain rates and high pressures. In this work, we systemically investigated the mechanical behaviors and underlying mechanisms of CoCrNi MEA and their connections under strain rates from 10⁻³ s⁻¹ to 10⁶ s⁻¹ and high pressures to about 22 GPa by experiments and simulations. The compression mechanical behaviors and microstructure characteristics were obtained by means of multiple loadings and characterization methods. As the strain rate increases, the experimental results showed two distinct dependences between yield strength and strain rates. Specifically, the strain rate sensitivity (SRS) of the yield strength transitions from 0.085 at low strain rates (1.0 × 10⁻³ s⁻¹-1.0 × 10⁻¹ s⁻¹) to 0.14 at high strain rates (2.6 × 10³ s⁻¹-1.48 × 10⁶ s⁻¹). Based on these, we utilized a crystal plasticity (CP) model and revealed that this transition of SRS is related to the mechanism transition from dislocation nucleation and slip at low strain rates to massive dislocation nucleation and drag at high strain rates. Our study provides a valuable framework for characterizing the dynamic mechanical behaviors of MEAs under a wider range of strain rates, guiding the design of MEAs with excellent dynamic mechanical properties.