Using Computation to Understand and Design New Materials Tailored for Extreme Environments

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1 Using Computation to Understand and Design New Materials Tailored for Extreme Environments Donald W. Brenner Kobe Steel Distinguished Professor Department of Materials Science and Engineering North Carolina State University, Raleigh, NC

2 Recent theory and modeling applications from our group: Vehicle Armor Detonation Nuclear Reactor Core Rocket nozzle Railgun In each case, computation can reach conditions that are difficult or impossible for experiment. 2

3 and sometimes materials testing by experiment is just illadvised. 3

4 We use a toolbox of computational methods: First Principles Density Functional Theory Semi-Empirical Electronic Structure Molecular Dynamics Simulations Hybrid Atomic+Continuum Mesoscale Analytic Modeling Pb in nanocrystalline Al Oxide Deposits on Nuclear Fuel Rods Sheared Al-Cu precipitate in an Al 2139 alloy 4

5 Three case studies: Formation of Bonaccordite on the fuel rods in nuclear reactors Advanced light-weight aluminum alloy armor Engineering entropy for ultra-high temperature applications 5

6 Consortium for the Advanced Simulation of Light Water Reactors 6

7 ~340 o C To steam generator Bundles of pencil thin 12 tall fuel rods ~293 o C ~155Bar (T B =345 o C) Turbulence Water from steam generator boiling from hot surface into a temperature gradient T>T B T<T B Chalk River Unidentified Deposit: CRUD ZrO 2, Fe 3 O 4, NiO, B 2 O 3, Li x B y O z, NiFe 2 O 4, Ni 2 FeBO 5 Bonaccordite? 7

8 Bonaccordite J.A. Sawicki, Journal of Nuclear Materials. 374 (2008) First i d in 1974, only found in Bon Accord, South Africa at meteorite impact site and deep in thick CRUD. Water insoluble; has been made by hydrothermal synthesis in alkaline conditions. Free energy of formation not measured What are the conditions in deep CRUD lead produce Bonaccordite? Total energies and other properties from first principles Density Functional Theory calculations. but what about extreme reactive conditions? 8

9 Compounds with known formation free energies Basic thermodynamics Reference Energy Known First-Principles Density Chemical potentials Functional Theory Energies Training set of 8 equations Chemical Potentials standard and state; 8 unknowns T, P, [] dependent at each T: Chemical potentials for Fe, O 2, H 2, Ni, Zn, Co, Li, B referenced to DFT energies. 9

10 We use a similar procedure for solution phase chemistry From database Unknown Chemical potentials from DFT training set Free energies of formation of aqueous species taken from a database (SUPCRT92) that includes high temperature and pressure data for aqueous ions calculated using the HKF (Helgeson- Kirkham-Flowers) equation of state. 10

11 Bonaccordite formation mechanisms: Deep CRUD conditions are significantly oxidizing compared to the conditions in the bulk coolant 11

12 Case Study #2: Al-Cu 2139 Alloy as Light Weight Vehicular Armor Mohammed Zikry, NC State Powerful IEDs required thicker steel plating on military vehicles, putting severe stress on vehicle suspension. The DoD had a critical need for light-weight vehicular armor that could be quickly deployed Al 2139 (AlCu 5 Mg 0.4 Ag 0.4 ) was known to have unique properties, especially at high strain rates. Joint Improvised Explosive Device Defeat Organization (JIEDDO) Academic Industrial DoD NCSU MSE NCSU MAE Cal. Tech MAE Atom Continuum High Strain Rate Modeling Plasticity Experiment ALCAN Processing Manufacturing Aberdeen PG Impact Testing 12

13 Al(2139) Alloy rich multi-scale micro/nano-structure AlCu 5 Mg 0.5 Ag 0.4 Combined presence of Mg+Ag promotes large amounts of new CuAl 2 W phase W phase has hexagonal plate-like shape with broad face aligned along the Al (111) planes, thickness < 6 nm - nanophase DFT Interface energies: θ : 0.17 J/m 2 W : 0.32 w/o Mg-Ag bilayer, W : 0.13 with bilayer 13

14 High Resolution TEM Image after shock loading Molecular simulation of shock loading Thin plate cutting without losing contact is consistent with HR-TEM images. Collective this step-ladder effect at the nanometer scale can retard shear localization on the micron-scale and strengthen the alloy without making it brittle. Molecular dynamics simulation. Aluminum matrix atoms only shown when part of a defected structure 14

15 Molecular simulation of shear-driven dislocation intersecting an Omega precipitate Simulations show dislocation pinning/orowan loop formation and permanent precipitate shearing. Conventional precipitate strengthened materials show one or other the other depending on the precipidate size. Seeing both here is likely from the large aspect ratio and nanoscale precipitate thickness. These in turn arise from the unique bilayer structure and lattice commensurability between the Omega broad face and Al matrix 15

16 230 D=10nm precipitate D=6nm precipitate 220 CRSS simulation x10 5 2x10 5 3x10 5 Strain Rate 16

17 Al2139 was so successful that it quickly passed the military specification process and was deployed as vehicular armor.and our funding for basic DoD research was discontinued. For the Multi-variant Heavy Expanded Mobility Tactical Truck 17

18 Case Study 3: Designing Ultra-High Temperature Materials >300 materials with T m > 2000 o C o Performance also depends on mechanical stability, high thermal conductivity, thermal shock and oxidation resistance o Traditional choices from group IV-transition metal borides, SiC, nitrides based on thermalchemical-mechanical properties. o Advances in last ~50 years have largely pushed performance by optimizing composition, improving microstructure, and creating new consolidation & densification methods 18

19 Convention: Materials of greatest interest have the strongest chemical bonds. Refractory transition metal borides, carbides, nitrides with short & strong bonds, hybrid covalent/ ionic character, and very large, negative H. G = H T S Melting Defects What about engineering configurational disorder extreme entropy S? G = H T S Amount of additional entropy from melting and defect formation is reduced. High Entropy Material single lattice structure with >4 randomly distributed elements 19

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21 New High Entropy Materials Rock Salt Oxides: (Mg 0.1 Co 0.1 Ni 0.1 Cu 0.1 Zn 0.1 )O Sc, Li, Cr, Sb, Ge, Sn, Ca, Li-Ga Jon-Paul Maria, NC State Rock Salt Structure Oxygen FCC sublattice Entropic FCC cation sublattice High-Entropy Diborides: (Hf 0.2 Zr 0.2 Ta 0.2 Mo 0.2 Ti 0.2 )B 2 Jian Luo, UCSD Others: CALPHAD, HT-DFT Ken Vecchio, UCSD (Hf 0.1 Nb 0.1 Ta 0.1 V 0.1 Zr 0.1 )C 0.50 (Hf 0.1 Nb 0.1 Ta 0.1 Ti 0.1 Zr 0.1 ) N 0.25 C 0.25 (Nb Ta Ti V W )C Heat transfer through the continuous boride sub lattice (Y 0.1 Hf 0.1 Zr 0.1 Ce 0.1? 0.1 )O

22 Chemistry in Nuclear Reactors Department of Energy Chris O brien (Sandia), Zsolt Rak (NC State), Avinash Dongare (U Conn). Theoretical assessment of bonaccordite formation in pressurized water reactors, J. Nuclear Materials 474, 62 (2016). Vehicular Armor DoD/JIEEDO Mohammed Zikry (NC State MAE), Lipeng Sun (VeraChem), G. Ravichandran (Cal. Tech) Deformation mechanisms of an Omega precipitate in a high-strength aluminum alloy subjected to high strain rates, J. Materials Research 26, 487 (2011). High Temperature Materials Office of Naval Research Jon-Paul Maria (NC State), Zsolt Rak (NC State), Patrick Hopkins (U.Va.), Beth Opila (U.Va.), Jian Luo (UCSD), Ken Vecchio (UCSD), Stefano Curtarolo (Duke). Charge compensation and electrostatic transferability in three entropy-stabilized oxides: Results from density functional theory calculations, J. Applied Phys. 120, (2016) 22