Effects of strain rate, temperature and microstructure on mechanical properties of (CoCrNi)94Al3Ti3 medium-entropy alloy: Experiments and constitutive modeling

Abstract

Mechanical properties and microstructure evolution of as-cast, solution-treated and aged (CoCrNi)₉₄Al₃Ti₃ medium-entropy alloys (MEAs) are investigated under uniaxial compression at strain rates from 10⁻³ to 3700 s⁻¹ within temperatures from 123 to 573 K. Compared to the single-phase solution-treated MEA, spherical nanosized particles result in an increase in the yield stress approximately by 55% (to 586 MPa) and 73% (to 655 MPa) for the as-cast and aged (CoCrNi)₉₄Al₃Ti₃, respectively. At ambient temperature, the as-cast and aged alloys demonstrate significantly higher dynamic strain rate sensitivity. At a fixed strain rate, the yield strengths and flow stresses increase with decreasing temperature for all three alloys. The as-cast and aged alloys exhibit significantly higher yield strength primarily due to precipitation strengthening of the coherent ordered L1₂ precipitates. Dislocation slip dominates the plastic deformation and leads to the weak but apparent ⟨110⟩ texture along the loading direction, and no deformation twins are observed in all alloys. Besides, Khan-Liu constitutive models are developed and can well describe the plastic flow of three alloys over a wide range of strain rates and temperatures.