The microstructural evolutions of the BJP samples due

The microstructural evolutions of the BJP samples due to increasing sintering temperature from 1225°C to 1300°C are shown in Fig. 2. Sintered coupon samples were cut using a wire saw, mounted using epoxy and hardener, progressively ground up to grit-1200, polished to a final step of colloidal silica, and etched with a Kallings solution. We aimed to observe the effect of different sintering temperatures on the relative density, grain size, grain growth and pore size of the BJP sintered samples. Optical micrographs (Fig. 3) revealed that the maximum relative density of 95% and 99.2% were obtained at sintering temperatures of 1270°C and 1285°C for the WA and GA BJP samples, respectively. The micrographs (Fig. 3) also show increasing precipitation due to segregation of alloying elements inside the grains and/or at the grain boundaries for GA and WA samples as the sintering temperature was increased to 1300°C. Fig. 4 illustrates precipitation at the grain boundary of the WA sample sintered at 1300°C.
Acknowledgments This work was supported by Air Force Research Laboratory, United States [agreement number FA8650-12-2–7230], Commonwealth of Pennsylvania, acting through the Department of Community and Economic Development [Contract number C000053981], National Science Foundation, United States [grant number 1434077, REU supplement] (CH), and Swanson School of Engineering and Office of the Provost of the University of Pittsburgh, United States (ETH). We would like to thank S.D. Biery for particle size analysis.
Data We use density functional theory (DFT) to compute the effects of substitutional Al, B, Cu, Mn, and Si solutes, and octahedral betaxolol C and N solutes on the lattice parameters and elastic stiffness coefficients C of bcc Fe. The PureFe.csv file contains the computed lattice parameter, magnetic moment, C, and the derivatives of the C with respect to lattice parameter for pure Fe. The computational methodology we developed in Ref. [1] calculates a strain-misfit tensor for each solute which determines changes in the lattice parameter and volumetric contributions to the derivatives of the C with respect to solute concentration. We also compute chemical contributions from each solute to the derivatives of the C with respect to solute concentration. The sum of the volumetric and the chemical contributions gives the total derivatives of the C with respect to solute concentration. The SoluteEffects.csv file contains the diagonal components of the solute strain-misfit tensors and their average values, the volumetric and chemical contributions to the C derivatives, the sum of the two contributions, and direct calculations of the total derivatives birth rate encompass both contributions. We compute the solute data using 2×2×2 (16 atoms), 3×3×3 (54 atoms), and 4×4×4 (128-atom) supercells.
Computational methods We use the VASP code [2] to perform the DFT calculations. The calculation details, including the exchange-correlation functional, pseudopotentials, and all numerical convergence parameters used in generating the data, are given in Ref. [1]. The VASP input files INCAR and KPOINTS, and output files CONTCAR, OUTCAR, and OSZICAR for all the calculations are stored in the NIST dSpace repository (http://hdl.handle.net/11256/67), along with the analyzed data stored in the PureFe.csv and SoluteEffects.csv files. The repository also stores Unix shell scripts we developed for calculating the data in the CSV files from the raw VASP output files. The fundamental quantities necessary for computing strain misfit tensors and elastic stiffness coefficients are the numbers of atoms in the computational supercells, lattice parameters, applied strain magnitudes, and stresses. The scripts compute the elastic stiffness coefficients from derivatives of stress with respect to strain, approximated using a standard four-point central finite-difference formula [3]. Tables 1 and 2 list the properties contained in the PureFe.csv and SoluteEffects.csv files, respectively, along with identifying tags that label the properties in the files and their units.