WFU Physics Colloquium
TITLE: Guided Design of Materials: from the sublime (core-shell nanoparticles) to the ridiculous (High-Entropy Alloys*
SPEAKER: Professor Duane D. Johnson
F. Wendell Miller Professor,
Materials Science & Engineering, Iowa State University
Chief Scientist, Ames Laboratory/U.S. DOE,
Ames, Iowa
TIME: Wed. Sep. 20, 2017 at 4:00 PM
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)
There will be a reception with refreshments at 3:30 PM in the lounge. All interested persons are cordially invited to attend.
ABSTRACT
Since the Iron Age, complex alloying effects have yielded desirable and unusual behaviors whose origins were difficult to unravel. Here we address intriguing behavior from alloying that occur in metallic nanoparticles to bulk complex solid solutions.
Core-shell preferences in catalytic metallic nanoparticles have failed to be predicted/explained from almost two decade of experiments, theory, and data science. Yet, simple concepts reveal the key correlations that determine the preferences, and, as a result, such behavior is easily predicted with no calculations, as will be revealed. With today’s data-oriented focus, this shows the necessity for data mining rather than data searching.
High-Entropy Alloys –near equiatomic solid solutions with 5+ elements– have emerged as novel, complex alloys with a variety of attractive properties: simple structures, better mechanical response at higher temperatures, and good oxidation resistance. Alloys at the edge of entropic stability offer prospects to coax them along different transformation pathways. From a design perspective, little is exceptional about HEAs, save maximal entropy, offering a huge space to tune for optimal properties, with only slightly reduced entropy. “High-throughput” KKR-CPA multiple-scattering theory, a Green’s function electronic-structure method, is applied to predict electronic, structural, and enthalpy (global stability) information for N-component HEA, where the coherent potential approximation (CPA) handles chemical disorder during charge self-consistency. Additionally, KKR-CPA-based thermodynamic linear-response yields short-range order (local stability) to guide alloy design, dictated by N(N–1)/2 chemical pair correlations. We exemplify predictions to narrow the N-dimensional design space, and show some experimental validations.
*Supported by the U.S. DOE, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division for theory development, and by the Office of Fossil Energy, Cross-cutting Research program for code validation for HEAs and experimental validation. Ames Laboratory is operated for DOE by ISU under Contract DE-AC02- 07CH11358.