Exceptional Fracture Resistance of a High Entropy Alloy
The high-entropy alloy shows high fracture toughness (KJIc > 215 MPa.m1/2) at 77-293K, increasing fracture resistance ( J-integral) with crack extension, and an exceptional combination of toughness and strength relative to other materials.
A new alloy design concept, high-entropy alloys, yields a material with exceptional cryogenic fracture toughness (damage-tolerant) properties.
Significance and Impact
This alloy, unlike most materials, shows increasing strength, ductility and toughness with decreasing temperature, thereby opening a new alloy design space where the usual inverse correlation between strength and toughness can be broken.
High‐entropy alloys comprise equiatomic, multi‐element systems that can crystallize as a single phase, despite containing multiple elements with different crystal structures. A rationale for this is that the configurational entropy contribution to the total free energy in alloys with five or more major elements may stabilize the solid‐solution state relative to multi‐phase microstructures.
Here, Rob Ritchie's team examines a five‐element high‐entropy alloy, CrMnFeCoNi, which forms a single‐phase face‐centered cubic (fcc) solid solution, and reveal its exceptional damage tolerance with tensile strengths above 1 GPa and fracture toughness values exceeding 200 MPa.m^(1/2). These toughness values are not only among the highest reported for any material but also do not decrease at low temperatures, as is commonly the case for most matrials. Furthermore, the alloy's mechanical properties actually improve at cryogenic temperatures resulting from continuous steady strain hardening through a transition from planar‐slip dislocation activity at room temperature to deformation by mechanical nano‐twinning with decreasing temperature.