A5059416418- Machine Learning in Materials Science
- Shape Memory Alloy Transformations
- High-pressure geophysics and materials
- Magnetic and transport properties of perovskites and related materials
- Advanced Chemical Physics Studies
- nanoparticles nucleation surface interactions
- Intermetallics and Advanced Alloy Properties
- Advanced Materials Characterization Techniques
- Magnetic Properties and Applications
- Theoretical and Computational Physics
- Magnetic Properties of Alloys
- Microstructure and Mechanical Properties of Steels
- Microstructure and mechanical properties
- Magnetic properties of thin films
- High Temperature Alloys and Creep
- Hydrogen Storage and Materials
- High Entropy Alloys Studies
- Surface and Thin Film Phenomena
- X-ray Diffraction in Crystallography
- Quantum, superfluid, helium dynamics
- Advanced ceramic materials synthesis
- Rare-earth and actinide compounds
- Ferroelectric and Piezoelectric Materials
- Advanced Surface Polishing Techniques
- Force Microscopy Techniques and Applications
Ames Research Center
2021-2024
Ames National Laboratory
2014-2022
United States Department of Energy
2014-2021
Iowa State University
2014-2021
University of Illinois Urbana-Champaign
2002-2008
Abstract Multiprincipal-element alloys are an enabling class of materials owing to their impressive mechanical and oxidation-resistant properties, especially in extreme environments 1,2 . Here we develop a new oxide-dispersion-strengthened NiCoCr-based alloy using model-driven design approach laser-based additive manufacturing. This alloy, called GRX-810, uses laser powder bed fusion disperse nanoscale Y 2 O 3 particles throughout the microstructure without use resource-intensive processing...
MnBi has attracted much attention in recent years due to its potential as a rare-earth-free permanent magnet material. It is unique because coercivity increases with increasing temperature, which makes it good hard phase material for exchange coupling nanocomposite magnets. difficult obtain, partly the reaction between Mn and Bi peritectic, reacts readily oxygen. MnO formation irreversible harmful performance. In this paper, we report our efforts toward developing To date, high purity (>90%)...
The nudged-elastic band (NEB) method is modified with concomitant two climbing images (C2-NEB) to find a transition state (TS) in complex energy landscapes, such as those serpentine minimal path (MEP). If single image (C1-NEB) successfully finds the TS, then C2-NEB it too. However, improved stability of makes suitable for more cases, where C1-NEB misses TS because MEP and NEB directions near saddle point are different. Generally, not only but also guarantees, by construction, that approach...
This review of the current state magnetocalorics is focused on materials exhibiting a giant magnetocaloric response near room temperature. To be economically viable for industrial applications and mass production, should have desired useful properties at reasonable cost safe humans environment during manufacturing, handling, operational use, after disposal. The discovery novel followed by gradual improvement compositional adjustment thermal or mechanical treatment. Consequently, with time,...
In alloys cluster expansions (CE) are increasingly used to combine first-principles electronic-structure calculations and Monte Carlo methods predict thermodynamic properties. As a basis-set expansion in terms of lattice geometrical clusters effective interactions, the CE is exact if infinite, but tractable only truncated. Yet until now truncation procedure was not well defined did guarantee reliable truncated CE. We present an optimal for basis sets that provides thermodynamics. then...
We calculate the transition temperature versus concentration (${T}_{c}$ vs $c$) phase diagrams of several phase-segregating alloys [fcc Ca-Sr, Au-Pt, and Rh-(Pd,Cu,Ag,Au)] using a multiscale method combining first-principles calculations Monte Carlo via cluster expansion (CE). study Pd-Rh, with its well-known high-$T$ miscibility gap, to verify method's reliability. predict that Ca-Sr segregates at low temperatures. then show rapid estimate ${T}_{c}$ is obtained from enthalpies analytically...
The effect of the crystal structure ordered transition-metal phosphide catalysts on hydrogen-evolution reaction is investigated using single crystals iron-phosphide (FeP) and monoclinic nickel-diphosphide (<italic>m</italic>-NiP<sub>2</sub>).
Abstract Almost 75 years of research has been devoted to producing superalloys capable higher operating temperatures in jet turbine engines, and there is an ongoing need increase temperature further. Here, a new disk Nickel-base superalloy designed take advantage strengthening atomic-scale dynamic complexions. This local phase transformation provides the alloy with three times improvement creep strength over similar comparable single crystal blade at 760 °C. Ultra-high-resolution chemical...
Magnetic first-order phase transitions are key for the emergence of functionalities fundamental and applied significance, including magnetic shape memory as well magnetostrictive magnetocaloric effects. Such usually associated with thermomagnetic hysteresis. We report observation a transition in $\mathrm{P}{\mathrm{r}}_{2}\mathrm{In}$ from paramagnetic to ferromagnetic state at ${T}_{C}=57\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ without detectable hysteresis, which is also accompanied by...
The density functional theory was employed to study the stress-strain behavior and elastic instabilities during solid-solid phase transformation (PT) when subjected a general stress tensor, as exemplified for semiconducting Si I metallic II, where metallization precedes PT, so stressed can be metal. hydrostatic PT occurs at 76 GPa, while under uniaxial loading it is 11 GPa (3.7 mean pressure), 21 times lower. $\mathrm{Si}\text{ }\text{ }\mathrm{I}\ensuremath{\rightarrow}\mathrm{Si}\text{...
NiTi is the most used shape-memory alloy; nonetheless, a lack of understanding remains regarding associated structures and transitions, including their barriers. Using generalized solid-state nudged elastic band method implemented via density-functional theory, we detail structural transformations in relevant to shape memory: those between body-centered orthorhombic (bco) ground state newly identified stable austenite ("glassy" B2-like) structure, energy barriers (hysteresis) intermediate...
Low-temperature MnBi (hexagonal NiAs phase) exhibits anomalies in the lattice constants (a, c) and bulk elastic modulus (B) below 100 K, spin reorientation magnetic susceptibility maximum near 90 and, importantly for high-temperature applications, an increasing coercivity (unique to MnBi) above 180 K. We calculate total energy magneto-anisotropy (MAE) versus using DFT+U methods. reproduce explain all anomalies. predict that MAE increase due a, suggesting means improve permanent magnets.
MnBi attracts great attention in recent years for its potential as permanent magnet materials. phase is difficult to obtain because of the rather drastic peritectic reaction between Mn and Bi. In this paper, we report our effort on synthesizing high purity compound using conventional powder metallurgical approaches. Neutron diffraction was carried out investigate crystal nuclear structure obtained powder. The result shows that about 91 wt. % at 300 K, magnetic moment atom lattice 4.424 4.013...
Cubic $B2$ FeRh exhibits a metamagnetic transition [(111) antiferromagnet (AFM) to ferromagnet (FM)] around 353 K and remains structurally stable at higher temperatures. However, the calculated zero-Kelvin phonons of AFM exhibit imaginary modes $M$ points in Brillouin zone, indicating premartensitic instability, which is precursor martensitic transformation low Combining electronic-structure calculations with ab initio molecular dynamics, conjugate gradient relaxation, solid-state...
For molecular substances exhibiting harmonic and nonharmonic vibrations, we present a first-principles approach to predict enthalpy differences between phases at finite temperatures, including solid-solid melting. We apply it the complex hydride ${\mathrm{LiBH}}_{4}$. Using ab initio dynamics, structure for high-$T$ solid phase of lithium borohydride, propose an approximation account vibrations. then changes transition, melting, H-storage reaction, all in agreement with experiment.
The coexistence pressure of two phases is a well-defined point at fixed temperature. In experiment, however, due to non-hydrostatic stresses and stress-dependent potential energy barrier, different measurements yield ranges with hysteresis. Accounting for these effects, we propose an inequality comparison the theoretical value plurality measured intervals. We revisit decades experiments on bcc - hcp transformations in iron, which are sensitive conditions sample size. From...
Nitinol (NiTi), the most widely used shape-memory alloy, exhibits an austenite phase that has yet to be identified. The usually assumed structure is cubic B2, which imaginary phonon modes, hence it unstable. We suggest a stable on average B2 symmetry (observed by X-ray and neutron diffraction), but finite atomic displacements from ideal sites. proposed spectrum agrees with scattering, diffraction spectra in agreement XRD, energy relative ground state calorimetry data.
Formation energies of a number hcp-based Ag-Al structures are obtained from ab initio electronic-structure calculations and used within cluster expansion approach to construct an effective alloy Hamiltonian. found be inherently asymmetric versus composition, providing incipient tendency for precipitation in Al-rich alloy. Both ground-state search Monte Carlo simulations based on the determine metastable hcp phase diagram. A new equilibrium AgAl ground state is predicted zero-energy domain...