8/13 Speech

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Speaker: Professor Peter K. Liaw

Topic: Lattice Distortion in the NbTaTiV(Zr) Refractory High-entropy Alloys

SpeakerProfessor Peter K. Liaw

OrganizationDepartment of Materials Science and Engineering, The University of Tennessee, Knoxville, USA

TopicLattice Distortion in the NbTaTiV(Zr) Refractory High-entropy Alloys

DatePM 2:00 , 2019.8.13

LocationRoom 228, College of Engineering


Peter K. Liaw was born in Chiayi, Taiwan. He graduated from the Chiayi High School, obtained his B.S. in Physics from the National Tsing Hua University, Taiwan, and his Ph.D. in Materials Science and Engineering from Northwestern University, USA.

After working at the Westinghouse Research and Development (R&D) Center for thirteen years, he joins the faculty and becomes an Endowed Ivan Racheff Chair of Excellence in the Department of Materials Science and Engineering at The University of Tennessee (UT), Knoxville, since March 1993. He has been working in the areas of fatigue, fracture, nondestructive evaluation, and life-prediction methodologies of structural alloys and composites. Since joining UT, his research interests include mechanical behavior, nondestructive evaluation, biomaterials, high-temperature alloys, bulk metallic glasses, high-entropy alloys, ceramic-matrix composites and coatings with the kindest and greatest help of his colleagues at UT and the near-by Oak Ridge National Laboratory, and around the world. He has published nine hundred and twenty-five journal papers, edited more than thirty books, and presented numerous plenary, keynote, and invited lectures at various national and international conferences, universities, and industries.

He was awarded the Royal E. Cabell Fellowship at Northwestern University. He is a recipient of numerous "Outstanding Performance" awards from the Westinghouse R&D Center. He was the Chairman of the TMS (The Minerals, Metals and Materials Society) "Mechanical Metallurgy" Committee, and the Chairman of the ASM (American Society for Metals) "Flow and Fracture" Committee. He has been the Chairman and Member of the TMS Award Committee on "Application to Practice, Educator, and Leadership Awards." He is a Fellow of ASM and TMS. He has been given the Outstanding Teacher Award, the Moses E. and Mayme Brooks Distinguished Professor Award, the Engineering Research Fellow Award, the National Alumni Association Distinguished Service Professor Award, the John Fisher Professorship, and L. R. Hesler Award at UT, and the TMS Distinguished Service Award.

He has been the Director of the National Science Foundation (NSF) Integrative Graduate Education and Research Training (IGERT) Program, the Director of the NSF International Materials Institutes (IMI) Program, and the Director of the NSF Major Research Instrumentation (MRI) Program at UT. Several of his graduate students have been given awards for their research and presentations at various professional societies and conferences. Moreover, his students are teaching and doing research at universities, industries, and government laboratories.


The mixing entropy in high-entropy alloys (HEAs) can be maximized by forming a stable single phase with multiple principal elements. The resultant effects, such as lattice distortion, can contribute to excellent mechanical properties, which has motivated numerous efforts to develop and design single-phase HEAs. However, challenges still remain, particularly on quantifying the lattice distortion and relating it to materials properties. In this study, we have developed a NbTaTiV refractory HEA with a single body-centered-cubic (BCC) structure using integrated experimental and computational approaches. The alloy was subjected to the proper homogenization treatment to eliminate the structural inhomogeneity and chemical segregation. Importantly, results indicate that this HEA exhibits extraordinary mechanical properties at both room and elevated temperatures. Furthermore, the effects of the high mixing entropy on the mechanical properties are further discussed and quantified in terms of lattice distortions and interatomic interactions of the NbTaTiV(Zr) HEAs via first-principles calculations.

This comprehensive study provides a method for the design and development of the single-phase BCC solid-solution phase refractory HEA, using an integrated experimental and theoretical thermodynamic-calculation approach. The results of the atom probe tomography (APT) measurement and the neutron-diffraction patterns indicate that the structure is composed of a single-phase BCC solid solution as well as a homogeneous elemental distribution with equimolar ratios. Furthermore, the mechanical-test results of the homogenization-treated sample show the excellent yield strength and plasticity at room-temperature (RT) as well as elevated temperatures. The dominant strengthening mechanism was found to be solid-solution hardening, which stems from the distortion of the crystalline lattice during deformation. It is thought that this strengthening mechanism induces slow elemental diffusion at high temperatures, which, consequently, leads to the strong resistance of high-temperature softening. The distorted lattice for this alloy system was quantitatively measured and calculated by the mathematical computation, neutron/synchrotron diffractions, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and theoretical modeling, such as first-principles calculations. The results of the above modeling and analysis indicate that the local severe lattice distortions are induced, due to the local atomic interactions in the homogenization-treated NbTaTiV(Zr) refractory HEAs. These results provide (1) a novel alloy-design strategy, (2) a fundamental understanding of the lattice-distortion effect on mechanical properties, and (3) a road map to produce better materials for high-temperatures application.