The paper presents the results of molecular dynamics study of the viscosity of nickel-containing binary metal melts for a wide range of temperatures, including the region of the equilibrium liquid phase and supercooled melt. It is shown that the temperature dependencies of the viscosity of binary metal melts are described by the Kelton's quasi-universal model. Based on the analysis of the viscosity coefficient of the binary melt composition within the framework of the Rosenfeld's scale transfor\-mations, it has been established that to correctly describe the viscosity of binary/multi\-component metal melts within the framework of entropy models, it is necessary to use a more complex representation of the excess entropy $S_{ex}$ than in the approximation of pair correlation entropy $S_2$.
We report the measurements of the thermal conductivity ($κ$) of iron (Fe) and nickel (Ni) at high pressures and high temperatures. $κ$ values are estimated from the temperature measurements across the sample surface in a laser heated diamond anvil cell (LHDAC) and using the COMSOL software. Near-isothermal $κ$'s are observed to increase with pressure in both the metals due to the increase of density of the pressed metals. In both metals $κ$'s are observed to follow a sharp fall during melting at different pressure points and are consistence with the other multi-anvil measurements. Constant val…
We consider the surface melting of metal nanowires by solving a phenomenological two-parabola Landau model and by conducting molecular dynamics simulations of nickel and aluminium nanowires. The model suggests that surface melting will precede bulk melting when the spreading parameter $Δγ$ for the melt in contact with the solid surface is positive (i.e. if the melt wets or partially wets the surface) and the wire is sufficiently thick, as is the case for planar surfaces and sufficiently large nanoparticles. Surface melting does not occur if $Δγ$ is negative. We test this model, which assumes t…
The carbon rich phase diagrams of nickel-carbon nanoparticles, relevant to catalysis and catalytic chemical vapor deposition synthesis of carbon nanotubes, are calculated for system sizes up to about 3 nanometers (807 Ni atoms). A tight binding model for interatomic interactions drives the Grand Canonical Monte Carlo simulations used to locate solid, core/shell and liquid stability domains, as a function of size, temperature and carbon chemical potential or concentration. Melting is favored by carbon incorporation from the nanoparticle surface, resulting in a strong relative lowering of the eu…
A crystal of pure nickel grows from its melt at a rate that reaches 70 meters per second. This extraordinary growth rate has led to the suggestion that metallic crystals might provide the next generation of phase change materials. The huge crystal growth rates of metals are a consequence of kinetics without activated control, in sharp contrast to the prediction of the classic theory of crystal growth. While the existence of growth kinetics without barriers is now well established in atomic melts, no physical explanation for the absence of an activation barrier to ordering has been established.…
We have demonstrated a new method for the large-area graphene growth, which can lead to a scalable low-cost high-throughput production technology. The method is based on growing single-layer or few-layer graphene films from a molten phase. The process involves dissolving carbon inside a molten metal at a specified temperature and then allowing the dissolved carbon to nucleate and grow on top of the melt at a lower temperature. The examined metals for the metal - carbon melts included copper and nickel. For the latter, pristine single layer graphene was grown successfully. The resulting graphen…
Additive manufacturing (AM) processes produce parts with improved physical, chemical, and mechanical properties compared to conventional manufacturing processes. In AM processes, intricate part geometries are produced from multicomponent alloy powder, in a layer-by-layer fashion with multipass laser melting, solidification, and solid-state phase transformations, in a shorter manufacturing time, with minimal surface finishing, and at a reasonable cost. However, there is an increasing need for post-processing of the manufactured parts via, for example, stress relieving heat treatment and hot iso…
Silica is known as the archetypal strong liquid, exhibiting an Arrhenius viscosity curve with a high glass transition temperature and constant activation energy. However, given the ideally isostatic nature of the silica network, the presence of even a small concentration of defects can lead to a significant decrease in both the glass transition temperature and activation energy for viscous flow. To understand the impact of trace level dopants on the viscosity of silica, we measure the viscosity-temperature curves for seven silica glass samples having different impurities, including four natura…
A novel y-y'-y" dual-superlattice superalloy, with promising mechanical properties up to elevated temperatures was recently reported. The present work employs state of the art chemical and spatial characterization techniques to study the effect systematic additions of Mo, W and Fe and variations in Nb and Al contents have on the phase fraction, thermal stability, elemental partitioning and mechanical properties. Alloys were produced through arc melting followed by heat treatment. Multi-scale characterization techniques and hardness testing were employed to characterize their microstructure, th…
Boron-doped molybdenum silicides have been already recognized as attractive candidates for space and ground ultra-high temperature applications far beyond limits of state-of-the-art nickel based superalloys. In this work, we are exploring a new method for fabricating Mo-Si-B alloys (as coatings or small bulk components) by utilizing a pressure-less reactive melt infiltration approach. The basic assumption of this approach is a synthesis of binary and/or ternary and complex intermetallic phases (silicides, borides, borosilicides), through a direct interaction of Si-B melt with molybdenum . The …
Retrofitting a commercial RF induction generator into a computer-controlled, vacuum and gas integrated annealing system for reactive-metal grain growth
Atomistic simulations provide insights into structure-property relations on an atomic size and length scale, that are complementary to the macroscopic observables that can be obtained from experiments. Quantitative predictions, however, are usually hindered by the need to strike a balance between the accuracy of the calculation of the interatomic potential and the modelling of realistic thermodynamic conditions. Machine-learning techniques make it possible to efficiently approximate the outcome of accurate electronic-structure calculations, that can therefore be combined with extensive thermod…
GdCo$_5$ may be considered as two sublattices - one of Gd and one of Co - whose magnetizations are in antiparallel alignment, forming a ferrimagnet. Substitution of nickel in the cobalt sublattice of GdCo$_5$ has been investigated to gain insight into how the magnetic properties of this prototype rare-earth/transition-metal magnet are affected by changes in the transition metal sublattice. Polycrystalline samples of GdCo$_{5-x}$Ni$_x$ for 0 $ \leq x \leq $ 5 were synthesized by arc melting. Structural characterization was carried out by powder x-ray diffraction and optical and scanning electro…
