Nanoscale Origins of the Exceptional Damage Tolerance of High-Entropy Alloys
TEM images captured from an in-situ TEM movie showing the nanoscale tensile loading of nano ‘fibres’ that bridge the crack in the near-tip region. Nanotwins can be seen to form in some of the fibres, enhancing their ductility and resulting in their significant elongation. .
In situ strength/fracture testing in an aberration-corrected transmission electron microscope (TEM) reveals a unique synergy of multiple deformation mechanisms that are the nanoscale basis of the exceptional ductility and toughness of high-entropy alloy CrMnFeCoNi.
Significance and Impact
This new class of materials shows remarkable combinations of strength, ductility and toughness, especially at cryogenic temperatures, which are unmatched compared to traditional metallic alloys.
- The strength and ductility of these alloys result from continuous strain hardening, which can be related to specific and unusual deformation mechanisms, including the easy motion of partial dislocations (to form stacking faults) coupled with their arrest by the slow planar slip of un-dissociated dislocations.
- Nanoscale crack bridges were seen to form at the tip of growing cracks. This is extremely unusual for a metallic material and serves to significantly increase fracture toughness.