@article{niu_zaddach_koch_irving_2016, title={First principles exploration of near-equiatomic NiFeCrCo high entropy alloys}, volume={672}, ISSN={["1873-4669"]}, DOI={10.1016/j.jallcom.2016.02.108}, abstractNote={High entropy alloy NiFeCrCo was systematically studied in the range of near-equal atomic concentrations, i.e., 10–40 at.%, by first-principles tools and high throughput calculations. Enthalpy of mixing, lattice parameter (a0), bulk modulus (B), and shear modulus (G) were calculated by the exact muffin-tin orbital method combined with coherent potential approximation (EMTO-CPA) for over 2700 compositions of the NiFeCrCo alloy as a single-phase solid solution in paramagnetic state. It was found that certain elements have the most significant influence on each property, namely, Cr on enthalpy of mixing, Co on a0, Fe on B, Co on G, and Cr on the ratio of B/G. An equation to predict the enthalpy of mixing by use of binary enthalpy data was evaluated and was found to have a good accuracy with a root-mean-square deviation (RMSD) of 42 meV per formula unit in the prediction. A similar equation to predict bulk modulus with weighted contribution from first–shell interaction is proposed and tested on all alloys. This equation was also found to be accurate with a RMSD of 6 GPa. Finally, it was found that shear moduli of all tested alloys are largely dependent on C44, while the concentration of Co has a noticeable control on C44. Spin polarized calculations were performed for a select group of alloys with both EMTO-CPA and the Vienna ab-initio Simulation Package (VASP) with special quasi-random structure models for comparison. Good agreement was found between these methods.}, journal={JOURNAL OF ALLOYS AND COMPOUNDS}, author={Niu, C. and Zaddach, A. J. and Koch, C. C. and Irving, D. L.}, year={2016}, month={Jul}, pages={510–520} }
 @article{zaddach_niu_oni_fan_lebeau_irving_koch_2016, title={Structure and magnetic properties of a multi-principal element Ni-Fe-Cr-Co-Zn-Mn alloy}, volume={68}, ISSN={["1879-0216"]}, DOI={10.1016/j.intermet.2015.09.009}, abstractNote={A nanocrystalline alloy with a nominal composition of Ni20Fe20Cr20Co20Zn15Mn5 was produced by mechanical alloying and processed using annealing treatments between 450 and 600 °C for lengths from 0.5 to 4 h. Analysis was conducted using x-ray diffraction, transmission electron microscopy, magnetometry, and first-principles calculations. Despite designing the alloy using empirical high-entropy alloy guidelines, it was found to precipitate numerous phases after annealing. These precipitates included a magnetic phase, α-FeCo, which, after the optimal heat treatment conditions of 1 h at 500 °C, resulted in an alloy with reasonably good hard magnetic properties. The effect of annealing temperature and time on the microstructure and magnetic properties are discussed, as well as the likely mechanisms that cause the microstructure development.}, journal={INTERMETALLICS}, author={Zaddach, A. J. and Niu, C. and Oni, A. A. and Fan, M. and LeBeau, J. M. and Irving, D. L. and Koch, C. C.}, year={2016}, month={Jan}, pages={107–112} }
 @article{youssef_zaddach_niu_irving_koch_2015, title={A Novel Low-Density, High-Hardness, High-entropy Alloy with Close-packed Single-phase Nanocrystalline Structures}, volume={3}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2014.985855}, abstractNote={A low-density, nanocrystalline high-entropy alloy, Al20Li20Mg10Sc20Ti30 was produced by mechanical alloying. It formed a single-phase fcc structure during ball milling and transformed to single-phase hcp upon annealing. The alloy has an estimated strength-to-weight ratio that is significantly higher than other nanocrystalline alloys and is comparable to ceramics. High hardness is retained after annealing.}, number={2}, journal={MATERIALS RESEARCH LETTERS}, author={Youssef, Khaled M. and Zaddach, Alexander J. and Niu, Changning and Irving, Douglas L. and Koch, Carl C.}, year={2015}, pages={95–99} }
 @article{niu_zaddach_oni_sang_hurt_lebeau_koch_irving_2015, title={Spin-driven ordering of Cr in the equiatomic high entropy alloy NiFeCrCo}, volume={106}, ISSN={["1077-3118"]}, DOI={10.1063/1.4918996}, abstractNote={Spin-driven ordering of Cr in an equiatomic fcc NiFeCrCo high entropy alloy (HEA) was predicted by first-principles calculations. Ordering of Cr is driven by the reduction in energy realized by surrounding anti-ferromagnetic Cr with ferromagnetic Ni, Fe, and Co in an alloyed L12 structure. The fully Cr-ordered alloyed L12 phase was predicted to have a magnetic moment that is 36% of that for the magnetically frustrated random solid solution. Three samples were synthesized by milling or casting/annealing. The cast/annealed sample was found to have a low temperature magnetic moment that is 44% of the moment in the milled sample, which is consistent with theoretical predictions for ordering. Scanning transmission electron microscopy measurements were performed and the presence of ordered nano-domains in cast/annealed samples throughout the equiatomic NiFeCrCo HEA was identified.}, number={16}, journal={APPLIED PHYSICS LETTERS}, author={Niu, C. and Zaddach, A. J. and Oni, A. A. and Sang, X. and Hurt, J. W., III and LeBeau, J. M. and Koch, C. C. and Irving, D. L.}, year={2015}, month={Apr} }
 @article{zaddach_scattergood_koch_2015, title={Tensile properties of low-stacking fault energy high-entropy alloys}, volume={636}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2015.03.109}, abstractNote={An equiatomic NiFeCrCoMn alloy, two non-equiatomic NiFeCrCoMn alloys optimized for low stacking fault energy, and an equiatomic NiFeCrCo alloy were produced by arc melting. Samples were homogenized, cold rolled, and annealed at temperatures between 575 and 1100 °C. Samples annealed at a moderate temperature near their recrystallization temperature (625–675 °C) and 1100 °C were cut into flat tensile samples and tested at a strain rate of 7.3×10−4 s−1. Equiatomic NiFeCrCo had the highest ductility and toughness after annealing at both temperatures, followed by Ni18.5Fe18.5Cr18.5Co26Mn18.5. Ni14Fe20Cr26Co20Mn20 exhibited poor thermal stability, forming σ-phase intermetallics at temperatures below 1100 °C. Observation of the fracture surfaces suggested that the high performance of NiFeCrCo might be due to the absence of oxide particles that form in the Mn-containing alloys. The strain-hardening rate and exponent were calculated from the results, showing a large deviation from typical behavior and significant grain size dependence.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Zaddach, A. J. and Scattergood, R. O. and Koch, C. C.}, year={2015}, month={Jun}, pages={373–378} }
 @article{zaddach_niu_koch_irving_2013, title={Mechanical Properties and Stacking Fault Energies of NiFeCrCoMn High-Entropy Alloy}, volume={65}, ISSN={1047-4838 1543-1851}, url={http://dx.doi.org/10.1007/S11837-013-0771-4}, DOI={10.1007/s11837-013-0771-4}, number={12}, journal={JOM}, publisher={Springer Science and Business Media LLC}, author={Zaddach, A. J. and Niu, C. and Koch, C. C. and Irving, D. L.}, year={2013}, month={Oct}, pages={1780–1789} }