Dislocation mechanisms and 3D twin architectures generate exceptional strength-ductility-toughness combination in CrCoNi medium-entropy alloy

• Published in: Nature communications Vol. 8; no. 1; p. 14390
• Main Authors: Zhang, Zijiao, Sheng, Hongwei, Wang, Zhangjie, Gludovatz, Bernd, Zhang, Ze, George, Easo P., Yu, Qian, Mao, Scott X., Ritchie, Robert O.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 20.02.2017; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/1023; 639/925; Alloys; Approximation; Deformation; Ductility; Energy; Engineering; Entropy; Humanities and Social Sciences; MATERIALS SCIENCE; Mechanical properties; Microscopy; multidisciplinary; Nanoscience and technology; Science; Science (multidisciplinary); Structural materials; United States > US; China; California
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms14390

Combinations of high strength and ductility are hard to attain in metals. Exceptions include materials exhibiting twinning-induced plasticity. To understand how the strength-ductility trade-off can be defeated, we apply in situ , and aberration-corrected scanning, transmission electron microscopy to examine deformation mechanisms in the medium-entropy alloy CrCoNi that exhibits one of the highest combinations of strength, ductility and toughness on record. Ab initio modelling suggests that it has negative stacking-fault energy at 0K and high propensity for twinning. With deformation we find that a three-dimensional (3D) hierarchical twin network forms from the activation of three twinning systems. This serves a dual function: conventional twin-boundary (TB) strengthening from blockage of dislocations impinging on TBs, coupled with the 3D twin network which offers pathways for dislocation glide along, and cross-slip between, intersecting TB-matrix interfaces. The stable twin architecture is not disrupted by interfacial dislocation glide, serving as a continuous source of strength, ductility and toughness. Materials that show twinning-induced plasticity can offer unusual combinations of strength and ductility. Here, authors study deformation twinning and dislocation behaviour in a medium-entropy alloy CrCoNi and find a three-dimensional (3D) hierarchical twin network that forms from the activation of three twinning systems.