Abstract
Deformation in the model high entropy alloy CoCrFeMnNi is assessed using an internal state variable constitutive model. A remarkable property of these alloys is the extraordinarily high strain hardening rates they experience in the plastic region of the stress strain curve. Published stress-strain measurements over a range of temperatures are analyzed. Dislocation obstacle interactions and the observed high rate of strain hardening are characterized in terms of state variables and their evolution. A model that combines a short-range obstacle and a long-range obstacle is shown to match experimental measurements over a wide range of temperatures and grain sizes. The long-range obstacle is thought to represent interactions of dislocations with regions of incomplete mixing or partial segregation. Dynamic strain aging also is observed at higher temperatures. Comparisons with measurements in austenitic stainless steel show some common trends.
Highlights
In recent years there has been increased interest in the materials engineering community in a class of metals known as High-Entropic Alloys
2800 2500 2500 2500 2500 2500 2500 2500 2500 2500 2500 2200 2200 2300 2300 both the HEA 1 and FG and CG materials) fall along the line represented by Equation (7), but other data points fall well off this line. The line in this figure is characterized by σεs0 = 3320 MPa, ε εs0 = 1×107 s−1, and gεs0 = 0.267
The behavior observed in the systems presented has been noted as similar to other highly entropic face-centered cubic (FCC) metals, e.g. austenitic stainless steel
Summary
These alloys often concurrently possess high strength and good ductility [1], properties which are typically inversely related For this result to manifest, the alloy’s solid solution phase should consist of a simple crystal structure with abundant slip systems. This report will focus upon a specific high-entropy system CoCr FeMnNi studied by Otto et al [2] and CoCrFeNi (referred to as HEA 1) studied by Licavoli et al [3] For these two alloys, the comprising chemistry is nearly equiatomic, i.e., 20% for each element in CoCrFeMnNi and 25% in CoCrFeNi. The high mixing entropies of each alloy allow for the overcoming of enthalpies of formation of compounds, resulting in a single-phase with a high microstructural stability, even at elevated temperatures [4]. Data was presented in engineering stress versus strain converted to true stress versus strain for the modeling
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