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

Mechanical properties and microstructure evolution of as-cast, solution-treated and aged (CoCrNi) ₉₄Al ₃Ti ₃ 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) ₉₄Al ₃Ti ₃, 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 L1 ₂ 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.