Dear All,

You are cordially invited to the Department of Materials Science and Engineering seminar.

Speaker: Dr. Sezer PICAK, Los Alamos National Laboratory/Iowa State University

Date: Friday, May 20, 2022

Time: 14:15

Place: Engineering Faculty D Block, Seminar room (1st Floor)

Best regards.

Deformation Behavior of Medium and High Entropy Alloys

Medium and high-entropy alloys (M/HEAs), unlike conventional alloys with one principal element, offer
a much larger design space with opportunities for discovering new functionalities and physics. The high
mixing entropy in M/HEAs favors the formation of a single-phase solid solution, providing a massive
number of alloying combinations. Moreover, the exceptional mechanical behavior of M/HEAs, which
makes them practically appealing, has been attributed to the fact that the cumulative interaction of the
different atoms within the first coordination shell creates a highly distorted lattice structure, and the strain
field created by this distortion plays an important role in strengthening by the impediment of dislocation
glide. In the present work, the deformation response of single-crystal M/HEAs is investigated, strained to
different deformation levels from the onset of plastic deformation to the failure, using transmission
electron microscopy (TEM), electron backscattered diffraction (EBSD), and high-energy synchrotron
transmission X-ray diffraction (XRD) observations. Experimental observations revealed that three major
mechanisms controlled the deformation stages in single-phase f.c.c M/HEAs, depending on the
orientation: (i) deformation twinning or ɛ-martensite transformation, (ii) planar slip, and (iii) dislocation
wall/network formation. The outstanding strength-ductility combination with anomalous strain-hardening
behavior in these materials has usually been linked to the activation of different kinds of deformation
modes triggered by low-energy stacking faults. However, the question still remains whether plasticity is
governed only by stacking fault energy or other intrinsic properties, in particular, atomic short-range order
(SRO). It has been interestingly observed that SRO promotes TWinning and Transformation induced
plasticity in M/HEAs. The current results demonstrate that the interplay of SRO with plasticity opens up
a new horizon for developing novel strategies to further understand and discover new M/HEA systems.
Ph.D., Sezer PICAK
Los Alamos National Laboratory/Iowa State University
Sezer Picak is a post-doctoral researcher in MST8, Los Alamos, NM. He was graduated from the
Department of Mechanical Engineering, Texas A& M University, Texas. His research interests include
the hardening behavior of Medium and High Entropy Alloys (M/HEAs), severe-plastic deformation in
M/HEAs, low-cycle fatigue response of M/HEAs, and direct TEM observation of microstructural
evolution in metallic systems.