Year: 2020

Development of New Aluminum Alloys

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Our group working with Collins Aerospace developed new aluminum alloys. The research was highlighted by ASM International.

https://www.asminternational.org/home/-/journal_content/56/10180/40278982/NEWS 

Study indicates AlCe and AlCo aluminum binary alloys could be suitable for 3D-printing

April 20, 2020
Source: ASM International

Researchers from the University of Connecticut, Pratt & Whitney, and Collins Aerospace collaborated in an 18-month study in which they used computational tools and a variety of experimental methods to develop simple aluminum binary alloys with properties similar or superior to commercial 6xxx aluminum alloys for additive manufacturing.

The goal was to identify binary systems of the type Al-X that promise hardness advantages after processing under conditions found in a typical metal additive manufacturing environment. DFT and laser surface glazing experiments were used to identify alloy additions to aluminum that induce lattice strains around solute atoms, and that can yield extended solid solubilities.

Given the non-equilibrium nature of rapidly quenched alloys, solid solutions with extended solubilities are metastable in nature and might transform further, for example, into microstructures with clusters or second-phase precipitates. The current work therefore represents an approach to the design of new aluminum alloys specific to non-equilibrium process technologies such as additive manufacturing.

Results show conclusively that cerium and cobalt are promising elements in next-generation aluminum alloys that make use of non-equilibrium processing conditions such as additive manufacturing.

The investigation started with an analysis of solid solution strengthening using first-principles calculations to determine elastic property changes and local lattice distortions from the introduction of different elements into a host aluminum lattice. These results, coupled with both equilibrium and nonequilibrium solubility data, led to the selection of cerium and cobalt as the primary candidate alloying elements. Alloys of Al\\Ce and Al\\Co at concentrations of 0.5, 1.0, and 3.0 at. % were then synthesized and subjected to laser glazing to produce non-equilibrium microstructures.

The microstructure and solid solution characteristics were determined using a combination of scanning electron microscopy and transmission electron microscopy. Hardness was measured by nanoindentation testing, which showed that both candidate systems harden significantly after glazing. In addition, Al-1.0Co at. % achieves a hardness comparable to Al6061-T6.

Following are comments from distinguished materials scientists regarding this study:

Prof. Rainer Hebert, Director – Pratt & Whitney Additive Manufacturing Center, Department of Materials Science and Engineering, University of Connecticut

“This is a comprehensive study where we developed simple Al-binary alloys with similar (if not superior) properties compared to commercial 6xxx series Al alloys. We collaborated extensively with Collins Aerospace and Pratt & Whitney. As such, this is also a great example of industry and academia working side by side in addressing a fundamental problem in metallurgy.”

Prof. Diran Apelian, Distinguished Professor of MSE, Chief Strategy Officer- SSoE, UCI, Irvine, Calif.

“Beauty is usually used as an adjective describing objects, individuals, nature; I will use it here to a manuscript as it exemplifies excellence and a set of standards for us to aspire. A “beautiful” paper in that the hypotheses, the experiments, coupled with a deep dive in ICME calculations, and validation in collaboration with industrial partners, have been executed in a compelling manner. The results are most meaningful and impactful. Accolades to our UConn colleagues.”

Prof. Lesley Frame, Director – Center for Materials Processing Data (CMPD), an ASM International Consortium; Department of Materials Science and Engineering, University
“Successful studies that identify improved methods for materials discovery like this one, illustrate the need for reliable methods of characterizing transient properties of the novel materials. CMPD is taking on the challenge of generating and validating the materials processing data that will support rapid transition from materials discovery to manufacturing application.”

Image: Ball-stick models for supercells constructed from a) 3 × 3 × 3 unit cell and b) 2 × 2 × 2 unit cell, containing 108 atoms and 32 atoms, respectively. The aluminum atoms are represented as smaller yellow balls and the X atom, where X represents elements with atomic number 1–94 (H\\Pu) other than aluminum in the periodic table, is represented by larger blue ball. The ball sizes are not representation of atomic sizes. Substituting one X atom in the supercells leads to concentration of 0.926 at. % and 3.13 at. % for 108 atoms and 32 atoms supercells, respectively.

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Full paper citation:

C. J Hung, S. K. Nayak, Y. Sun, C. Fennessy, V. K. Vedula, S. Tulyani, S.-W. Lee, S. P. Alpay, and R. J. Hebert, “Novel Al-X Alloys with Improved Hardness,” Materials & Design, 192, 108699 (2020); https://doi.org/10.1016/j.matdes.2020.108699

Thomas and Sanjeev Published in Physical Review B!

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This research is a uniquely rigorous and systematic study of the effect of exchange-correlation functionals (XCFs) (in the framework of density functional theory) on the outcome of geometric and electronic structure calculations in layered binary chalcogenide (A2B3) systems.

Abstract

Topological insulators (TIs) are materials that are insulating in the bulk but have zero band-gap surface states with linear dispersion and are protected by time-reversal symmetry. These unique characteristics could pave the way for many promising applications that include spintronic devices and quantum computations. It is important to understand and theoretically describe TIs as accurately as possible to predict properties. Quantum mechanical approaches, specifically first-principles density-functional-theory (DFT)-based methods, have been used extensively to model electronic properties of TIs. Here we provide a comprehensive assessment of a variety of DFT formalisms and how these capture the electronic structure of TIs. We concentrate on Bi2Se3 and Bi2Te3 as examples of prototypical TI materials. We find that the generalized gradient approximation (GGA) and kinetic density functional (metaGGA) increase the thickness of the TI slab, whereas we see the opposite behavior in DFT computations using LDA. Accounting for van der Waals (vdW) interactions overcomes the apparent over-relaxations and retraces the atomic positions toward the bulk. Based on a systematic computational study, we show that GGA with vdW treatment is an appropriate method for structural optimization. However, the vdW corrections recover the experimental bulk parameters, and do not influence the charge density implicitly. Thus, electronic structures derived from the base GGA functional, employing experimental lattice parameters, is sufficient.
DOI: https://doi.org/10.1103/PhysRevB.101.085140

Congrats! Ayana and Dennis Earn Top Distinction in Scientific Reports

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Ayana Ghosh’s and Dennis Trujillo’s article,  Electronic and Magnetic Properties of Lanthanum and Strontium Doped Bismuth Ferrite: A First-Principles Study, received 2,603 article downloads in 2019, placing it as one of the top 100 downloaded physics papers for Scientific Reports in 2019.

Scientific Reports published more than 1,072 physics papers in 2019, and so a position in the top 100 most downloaded articles is an extraordinary achievement.

Kevin, Sanjubala and Colleagues Published in Clays and Clay Minerals

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DFT was used to determine counter-hydrogen ion retention strength in Montmorillonite clays, a common aluminosilicate mineral found in soil, as a measure of cation adsorption strength. Results show that impurity Mg-Fe separation distance is responsible for three possible adsorption strengths regimes and are consistent with experimental data.

Abstract

Although multiple types of adsorption sites have long been observed in montmorillonite, a consistent explanation about the chemical structure of these adsorption sites has not yet been established. Identifying the cation interlayer adsorption sites based on the octahedral cation distribution on montmorillonite was investigated in this study by using a Density Functional Theory (DFT) simulation. A clay structural model (H[Al6MgFe]Si16O40(OH)8) with a similar composition to Wyoming SWy-1 montmorillonite was built, where two octahedral Al were respectively substituted by Fe and Mg, and H+ was the charge compensating cation. This model had twenty-one different possible configurations as a function of the distribution of octahedral Al, Fe, and Mg cations. The DFT simulations of 15 of these different configurations showed no preference for the formation of any configuration with a specific octahedral Fe-Mg distance. However, the H+ adsorption energy was separated into three distinct groups based on the number of octahedral jumps from Fe to Mg atoms. The H+ adsorption energy significantly decreased with increasing number of octahedral jumps from Fe to Mg. Assuming an even probability of occurrence of 21 octahedral structures in montmorillonite, the percentages of these three groups are 43, 43, and 14%, respectively, which are very close to the three major sites on montmorillonite from published cation adsorption data. These DFT simulations offer an entirely new explanation for the location and chemical structure of the three major adsorption sites on montmorillonite, namely, all three sites are in the interlayer, and their adsorption strengths are a function of the number of octahedral jumps from Fe to Mg atoms.