Mechanical properties of high-entropy alloys with emphasis on face-centered cubic alloys

• Published in: Progress in materials science Vol. 102; no. C; pp. 296 - 345
• Main Authors: Li, Zezhou, Zhao, Shiteng, Ritchie, Robert O., Meyers, Marc A.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier BV 01.05.2019; Elsevier
• Subjects: Alloy development; Alloy systems; Alloying elements; Alloys; Diffusion rate; Dynamic loads; Edge dislocations; Entropy; Fracture toughness; Hardening rate; High entropy alloys; Materials science; Mechanical properties; Shear bands; Shear strain; Shear strength; Twinning
• ISSN: 0079-6425; 1873-2208
• DOI: 10.1016/j.pmatsci.2018.12.003

High-entropy alloys (HEAs), also known as multi-principal element alloys or multi-component alloys, have been the subject of numerous investigations since they were first described in 2004. The earliest HEA was the equiatomic CrMnFeCoNi “Cantor” alloy, but HEAs now encompass a broad class of metallic and ceramic systems. The concept of utilizing the high entropy of mixing to develop stable multi-element alloys may not be scientifically correct but has produced extraordinary mechanical properties in specific HEAs, mainly CrCoNi-based alloys, associated with their continuous work-hardening rate that is sustained to large plastic strains (∼0.5) and at low temperatures. This, in combination with the high frictional forces on dislocations and a propensity for twinning, leads to outstandingly high fracture toughness values (exceeding 200 MPa·m1/2) and resistance to shear-band formation under dynamic loading. The critical shear strain for the onset of adiabatic shear band formation is ∼7 for the Cantor alloy, much higher than that for conventional alloys, suggesting superior ballistic properties. The slower diffusion rates resulting from the multi-element environment contribute to the excellent intermediate-temperature performance. We review the principal mechanical properties of these alloys with emphasis on the face-centered cubic systems, such as the CrCoNi-based alloys. Their favorable mechanical properties and ease of processing by conventional means suggest extensive utilization in many future structural applications.