The alloy-design strategy of combining multiple elements in near-equimolar ratios has shown great potential for producing exceptional engineering materials, often known as 'high-entropy alloys'. Understanding the elemental distribution, and, thus, the evolution of the configurational entropy during solidification, is undertaken in the present study using the Al 1.3 CoCrCuFeNi model alloy. Here we show that, even when the material undergoes elemental segregation, precipitation, chemical ordering and spinodal decomposition, a significant amount of disorder remains, due to the distributions of multiple elements in the major phases. The results suggest that the high-entropy alloy-design strategy may be applied to a wide range of complex materials, and should not be limited to the goal of creating single-phase solid solutions.

2The spontaneous imbibition of water and other liquids into gas-filled 3 fractures in variably-saturated porous media is important in a variety of 4 engineering and geological contexts. However, surprisingly few studies have 5 investigated this phenomenon. We present a theoretical framework for 6 predicting the 1-dimensional movement of water into air-filled fractures 7 within a porous medium based on early-time capillary dynamics and 8 spreading over the rough surfaces of fracture faces. The theory permits 9 estimation of sorptivity values for the matrix and fracture zone, as well as a 10 dispersion parameter which quantifies the extent of spreading of the wetting 11 front. Quantitative data on spontaneous imbibition of water in unsaturated 12 Berea sandstone cores were acquired to evaluate the proposed model. The 13 cores with different permeability classes ranging from 50 to 500 mD and 14 were fractured using the Brazilian method. Spontaneous imbibition in the 15 fractured cores was measured by dynamic neutron radiography at the 16 Neutron Imaging Prototype Facility (beam line CG-1D, HFIR), Oak Ridge 17 National Laboratory. Water uptake into both the matrix and the fracture 18 zone exhibited square-root-of-time behavior. The matrix sorptivities ranged 19 from 2.9 to 4.6 mm s -0.5 , and increased linearly as the permeability class 20 increased. The sorptivities of the fracture zones ranged from 17.9 to 27.1 21 mm s -0.5 , and increased linearly with increasing fracture aperture width. The 22 dispersion coefficients ranged from 23.7 to 66.7 mm 2 s -1 and increased 23 linearly with increasing fracture aperture width and damage zone width. 24 Both theory and observations indicate that fractures can significantly 25 increase spontaneous imbibition in unsaturated sedimentary rock by 26 capillary action and surface spreading on rough fracture faces. Fractures 27 also inrease the dispersion of the wetting front. Further research is needed 28 7

We present a neutron-scattering study of the quantum dynamics of molecular hydrogen trapped inside solid C 60. The loading isotherm is shown to deviate significantly from a standard Langmuir response and follows instead an exponential form, increasing from 40% filling at 130 atm to 90% at 700 atm. Diffraction data confirm that the adsorbed molecules are randomly oriented and sit exclusively at the octahedral site. Inelastic neutron scattering clearly shows the ortho to para conversion of the interstitial hydrogen, which occurs via a transition from the Jϭ1 to Jϭ0 rotational levels. The level scheme shows relatively minor deviations ͑on the order of a few percent͒ from the free rotor model with the splitting in the excited level being the same, 0.7 meV, for both H 2 and D 2. In contrast the shift in the overall level, which is shown to depend critically upon zero-point motion is almost three times greater for H 2 than D 2. We also identify the translational modes of the trapped molecules which occur at a much higher energy than would be classically predicted and have an isotopic shift on the order of ͱ2.2. Quantum-mechanical model calculations within the self-consistent harmonic approximation indicate that zero-point motion of H 2 molecules in the ground state play the central role in understanding the experimental results, and in particular the high energy of the translational modes and the magnitude of their isotopic shift. ͓S0163-1829͑99͒03133-1͔

The ability to predict and understand phases in high-entropy alloys (HEAs) is still being debated, and primarily true predictive capabilities derive from the known thermodynamics of materials. The present work demonstrates that prior work using high-throughput first-principles calculations may be further utilized to provide direct insight into the temperature- and composition-dependent phase evolution in HEAs, particularly Al-containing HEAs with a strengthening multiphase microstructure. Using a simple model with parameters derived from first-principles calculations, we reproduce the major features associated with Al-containing phases, demonstrating a generalizable approach for exploring potential phase evolution where little experimental data exists. Neutron scattering, in situ microscopy, and calorimetry measurements suggest that our high-throughput Monte Carlo technique captures both qualitative and quantitative features for both intermetallic phase formation and microstructure evolution at lower temperatures. This study provides a simple approach to guide HEA development, including ordered multi-phase HEAs, which may prove valuable for structural applications.

We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO(3), to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the first Ca-O peak in the pair distribution function of the melt compared to the glass, which comprises primarily of 6- and 7-fold coordinated Ca-polyhedra. The broadening can be explained by a redistribution of Ca-O bond lengths, especially toward longer distances in the liquid. The first order neutron difference function provides a test of recent molecular dynamics simulations and supports the MD model which contains short chains or channels of edge shared Ca-octahedra in the liquid state. It is suggested that the polymerization of Ca-polyhedra is responsible for the fragile viscosity behavior of the melt and the glass forming ability in CaSiO(3).

The microstructure and phase composition of an AlCoCrFeNi high-entropy alloy (HEA) were studied in as-cast (AlCoCrFeNi-AC, AC represents as-cast) and homogenized (AlCoCrFeNi-HP, HP signifies hot isostatic pressed and homogenized) conditions. The AlCoCrFeNi-AC ally has a dendritrical structure in the consisting primarily of a nano-lamellar mixture of A2 [disorder body-centered-cubic (BCC)] and B2 (ordered BCC) phases, formed by an eutectic reaction. The homogenization heat treatment, consisting of hot isostatic pressed for 1 hour at 1,100 °C, 207 MPa and annealing at 1,150 °C for 50 hours, resulted in an increase in the volume fraction of the A1 phase and formation of a Sigma () phase. Tensile properties in ascast and homogenized conditions are reported at 700 °C. The ultimate tensile strength was virtually unaffected by heat treatment, and was 396 ± 4 MPa at 700 °C. However, 2 homogenization produced a noticeable increase in ductility. The AlCoCrFeNi-AC alloy showed a tensile elongation of only 1.0 %, while after the heat-treatment, the elongation of AlCoCrFeNi-HP was 11.7 %. Thermodynamic modeling of non-equilibrium and equilibrium phase diagrams for the AlCoCrFeNi HEA gave good agreement with the experimental observations of the phase contents in the AlCoCrFeNi-AC and AlCoCrFeNi-HP. The reasons for the improvement of ductility after the heat treatment and the crack initiation subjected to tensile loading were discussed.

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