Dynamically coupled shear transformation mechanisms in deformation-induced hexagonal high-entropy alloys

Guest Speaker：Prof Jian Wang，University of Nebraska-Lincoln，USA

Inviter: Assoc. Prof. Yangxin Li

Date&Time: Thursday, 9.Jan., 10:00-11:30

Venue: Meeting Room 308 , Xu Zuyao Building

Biography:

Dr. Jian Wang is Wilmer J. and Sally L. Hergenrader Presidential Chair of Mechanical and Materials Engineering at the University of Nebraska-Lincoln since 2015. He received his PhD from Rensselaer Polytechnic Institute in 2006 and worked as technical staff member at Los Alamos National Laboratory (LANL) until 2015. His research focuses on quantitatively exploring the structure-properties relations of materials using multi-scale theory, modeling and experimental methods and techniques. He was awarded the LANL Distinguished Postdoctoral Performance Award (2009), the LDRD/Early Career Award (2011), TMS MPMD Young Leader Award (2013), International Plasticity Young Research Award (2015), Materials Today Rising Star Award in the category of Materials Genome Innovation (2018), TMS MPMD Distinguished Scientist Award (2022) and TMS BRIMACOMBE MEDALIST Award (2023). He is Fellow of ASME and Fellow of ASM International. He served as Editorial Board of International Journal of Plasticity (2015~), Materials Research Letters (2016~), and others. He has published more than ~360 peer-reviewed papers (> 24,000 citations and H-index = 88; 9 papers featured as Journal cover) and delivered 150+ invited/keynote lectures.

Abstract:

Deformation twinning (DT) and/or martensitic transformation (MT) accommodate plastic deformation in addition to dislocation slips in some crystalline materials. If reverse martensitic transformation (RMT) can be dynamically activated accompanied by DT and/or MT, RMT bands can act as barriers to the propagation of these shear bands, strengthening materials and enhancing the strain-hardening rate. Here, we unveil dynamically coupled shear transformation mechanisms in a CrMnFeCoNi high-entropy alloy (HEA) with a face-centered cubic (fcc) structure when deformed at 4.2 K, including coupled MT-RMT mechanisms between fcc and hexagonal close packed (hcp) phases, {1 1} and {2 1} DTs in deformed-induced hcp- phase grains, and coupled DTs-RMT within hcp-phase grains where kinematic paths of RMT are found to be related to twin boundaries. In addition, anomalous serrated flow behavior is characterized by a sudden stress drop, following a strain burst at the low-stress level, and then back to a higher flow stress level. The RMT is triggered by local dissipative heating generated by plastic deformation, resulting in anomalous softening accompanied by sudden stress drops and strain bursts, whereas numerous newly formed boundaries impede the propagation of twins and dislocation motions, resulting in exceptional strengthening and strain-hardening. These findings provide a fundamental understanding of sustainable strengthening and strain-hardening in HEAs at ultralow temperatures and offer a new strategy for designing advanced metallic alloys.