Strain-rate sensitivity of high-entropy alloys and its significance in deformation

Abstract

Strain-rate dependence in face centered cubic high entropy alloys still remains controversial despite extensive efforts on this topic. Strain-rate sensitivity reflects underlying thermally-activated deformation and the controversy boils down to the deformation mechanism. There has been disagreement even on the experimental values of the strain-rate sensitivity and activation volume. This study reviewed and analyzed the differences in experimental values and proposed mechanisms to resolve the controversy over the nature of thermal obstacles in CrMnFeCoNi alloy. TEM study on CrMnFe-CoNi supports the presence of nanoscale heterogeneity elucidating the nature of rate-controlling mechanism in the alloy. IMPACT STATEMENT Strong temperature dependence of flow stress, high strain-rate-sensitivity and small activationvolume are key features for deformation of CrMnFeCoNi. TEM analysis supports presence of nanoscale heterogeneity acting as the rate-controlling barrier.

Mechanically derived short-range order and its impact on the multi-principal-element alloys

“…The application of a higher έ increased the maximum tensile strength ( σ UTS ) and total elongation ( ε total ): σ UTS and ε total increased from 1202 MPa and 12% for HEA-L to 1385 MPa and 22% for HEA-H, respectively. The simultaneous increase in σ UTS and ε total caused by a higher έ is predictable for most fcc-based structural alloys, as a higher deformation rate under quasistatic conditions results in a more uniform distribution of dislocations under conditions of the same amount of strain 41 . Typically, a higher έ increases or decreases the 0.2% offset yield strength ( σ YS ) significantly for a given alloy composition, indicating a strong dependence of σ YS on the applied έ value 41 .…”

Data on the microstructure and deformation of Fe50Mn25Cr15Co10Nx (x=0∼1.6) supporting the modifications of partial-dislocation-induced defects (PDIDs) and strength/ductility enhancement in metastable high entropy alloys

“…The SRS at low strains of Fe 50 Mn 25 Cr 15 Co 10 N 1.6 (∼0.024) was close to those of Cantor alloy [11] , but it decreased more slowly than in Cantor alloy and the value (∼0.013) remained higher than Cantor at the strain of 0.3. The strain rate sensitivity of flow stress was found to decrease with strain as in equiatomic CoCrFeMnNi [10] . The enhanced ductility in Fe 50 Mn 25 Cr 15 Co 10 N 1.6 can be attributed partly to the enhanced strain rate sensitivity.…”

“…The strain rate sensitivity m was calculated based on the change of the flow stress obtained from the strain rate jump tests shown in Fig. S2 using the following equation [9 , 10] : where σ is the flow stress and is the strain rate. Repetitive strain rate jumps between 10 −3 S −1 and 10 −2 S −1 were carried out.…”

Mechanical Performance and Microstructural Evolution of (NiCo)75Cr17Fe8Cx (x = 0~0.83) Medium Entropy Alloys at Room and Cryogenic Temperatures

“…The strength enhancement of (NiCo) 75 Cr 17 Fe 8 , compared to Alloy 600 can be attributed to substitutional solution hardening and the effect of alloying on the slip planarity [35,37]. As can be seen in Figure 10, strength/ductility combinations of carbon-free (NiCo) 75 Cr 17 Fe 8 and carbon containing (NiCo) 75 Cr 17 Fe 8 C 0.34 and (NiCo) 75 Cr 17 Fe 8 C 0.83 (b) are also superior to those of Co-Cr-Ni-Fe HEAs [20,21,31,48,63] because of the strengthening contributions including ∆σ G by grain refinement, ∆σ P by carbides, ∆σ iS by interstitial solution strengthening by carbon and the friction stress by intrinsic stress and substitutional solid solution strengthening (σ 0 + ∆σ SS ). In this study, a new design strategy to develop a new medium entropy alloy by increasing the entropy of the conventional alloys by adding a new element with high solubility was found to be effective in enhancing the mechanical performance.…”

“…It is apparent that the predicted data are in reasonable agreement with the experimental results. In carbon-free (NiCo) 75 Cr 17 Fe 8 , the friction stress component consisting of the intrinsic stress and the solid solution strengthening increases significantly with the decrease of temperature, suggesting the strong temperature dependence of substitutional solid solution strengthening as in CoCrFeMnNi HEA [18,63]. The major contribution of carbon to strengthening is caused by grain-size refinement followed by precipitation strengthening by carbide formation in the grain interior as shown in Figure 10.…”