Abstract
Temperature is known to affect deformation mechanisms in metallic alloys. As temperature decreases, the stacking-fault energy in many face-centered cubic (fcc) alloys decreases, resulting in a change of deformation mode from dislocation slip to deformation twinning. Such an impact of temperature can be more complex in compositionally heterogeneous microstructures that exhibit, for example, local concentration fluctuation such as that in multi-principal element alloys. In this work, we compare the dislocation behavior and mechanical properties of a fcc Cr20Mn10Fe30Co30Ni10 high-entropy alloy at ambient and liquid-nitrogen temperatures. We find that a network of stacking faults is formed by uniformly extended dislocations at ambient temperatures with low stacking-fault energy, whereas at lower temperatures, uneven dissociation of dislocations becomes significant, which results in severe dislocation pile-ups together with their pronounced entanglement. Our findings indicate that as the stacking-fault energy decreases with decreasing temperature, the heterogeneity of the distribution of elements becomes more dominant in tuning the local variation of lattice resistance. As a result, the change in dislocation behavior at low temperatures strongly affects microstructural evolution and consequently leads to significantly more pronounced work hardening.
Highlights
For the CrMnFeCoNi system high-entropy alloys, in general, previous studies have reported that martensitic transformation occurs when the stacking-fault energy (SFE) is less than $20 mJ/m2, twin deformation prevails when the SFE is between 20 and 40 mJ/m2, and above $40 mJ/m2, the slip of full dislocations becomes the dominant deformation mechanism.4,9,10 For the equiatomic CrMnFeCoNi alloy, partial and full dislocation motion dominates deformation at ambient temperatures, whereas with decreasing temperature, the elevation in strength activates deformation twinning
We find that a network of stacking faults is formed by uniformly extended dislocations at ambient temperatures with low stacking-fault energy, whereas at lower temperatures, uneven dissociation of dislocations becomes significant, which results in severe dislocation pile-ups together with their pronounced entanglement
Since changing the ratio of elements and substituting or adding alloying elements in highentropy alloys (HEAs) can significantly vary the degree of local variations in chemical compositions,14,23 we investigate here the effects of temperature on the dislocation structure and slip behavior and the resulting evolution of dislocation networks in a Cr20Mn10Fe30Co30Ni10 HEA, a non-equiatomic variation of the Cantor alloy developed to promote a transformation-induced plasticity (TRIP) effect
Summary
For the CrMnFeCoNi system high-entropy alloys, in general, previous studies have reported that martensitic transformation occurs when the SFE is less than $20 mJ/m2, twin deformation prevails when the SFE is between 20 and 40 mJ/m2, and above $40 mJ/m2, the slip of full dislocations becomes the dominant deformation mechanism.4,9,10 For the equiatomic CrMnFeCoNi alloy, partial and full dislocation motion dominates deformation at ambient temperatures, whereas with decreasing temperature, the elevation in strength activates deformation twinning. We compare the dislocation behavior and mechanical properties of a fcc Cr20Mn10Fe30Co30Ni10 high-entropy alloy at ambient and liquid-nitrogen temperatures.
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