Pressure effect on the order–disorder transformation in L10 FeNi

The ordered phase of the FeNi system is known for its promising magnetic properties that make it a first-class rare-earth free permanent magnet. Mapping out the parameter space controlling the order–disorder transformation is an important step towards finding growth conditions that stabilize the $$L1_0$$ L 1 0 phase of FeNi. In this work, we study the magnetic properties and chemical order-disorder transformation in FeNi as a function of lattice expansion by utilizing ab initio alloy theory. The largest volume expansion considered here is 29% which corresponds to a pressure of $${-25}$$ - 25 GPa. The thermodynamic and magnetic calculations are formulated in terms of a long-range order parameter, which is subsequently used to find the ordering temperature as a function of pressure. We show that negative pressure promotes ordering, meaning that synthetic routes involving an increase of the volume of FeNi are expected to expand the stability field of the $$L1_0$$ L 1 0 phase.

Kinetic transition in the order–disorder transformation at a solid/liquid interface

Phase-field analysis for the kinetic transition in an ordered crystal structure growing from an undercooled liquid is carried out. The results are interpreted on the basis of analytical and numerical solutions of equations describing the dynamics of the phase field, the long-range order parameter as well as the atomic diffusion within the crystal/liquid interface and in the bulk crystal. As an example, the growth of a binary A 50 B 50 crystal is described, and critical undercoolings at characteristic changes of growth velocity and the long-range order parameter are defined. For rapidly growing crystals, analogies and qualitative differences are found in comparison with known non-equilibrium effects, particularly solute trapping and disorder trapping. The results and model predictions are compared qualitatively with results of the theory of kinetic phase transitions (Chernov 1968 Sov. Phys. JETP 26 , 1182–1190) and with experimental data obtained for rapid dendritic solidification of congruently melting alloy with order–disorder transition (Hartmann et al. 2009 Europhys. Lett. 87 , 40007 ( doi:10.1209/0295-5075/87/40007 )). This article is part of the theme issue ‘From atomistic interfaces to dendritic patterns’.

Microscopic and Surface Properties of K-Na Liquid Alloys

The deviation from ideal mixture behavior and concentration dependent symmetry in the microscopic and surface properties of K-Na liquid alloy is investigated within a simple statistical model. The concentration dependent of microscopic functions(concentration fluctuation in the long wavelength limit, Warren-Cowley short range order parameter) and surface properties(surface concentration and surface tension) has got special attention to show a tendency of like atom pairing in the mixture. The theoretical analysis reveals that energy parameter is temperature dependent, K-Na alloys is of weakly interacting system and K-atoms segregates on the surface of K-Na liquid alloys at bulk concentration of Na.The Himalayan Physics Vol. 4, No. 4, 2013 Page: 40-45 Uploaded date: 12/23/2013

The investigation of the microstructure and mechanical properties of ordered alominide-iron (boron) nanostructures produced by mechanical alloying and sintering

In this study, mechanical alloying (MA) of Fe -50 Al , Fe -49.5 Al -1 B , and Fe -47.5 Al -5 B (at.%) alloy powders and mechanical properties of sintered products of the as-milled powders were investigated. X-ray diffraction (XRD) results showed the addition of B caused more crystallite refinement compared to the B -free powders. To consider the sintering and ordering behaviors of the parts produced from cold compaction of the powders milled for 80 h, sintering was conducted at various temperatures. It was found that the sintering temperature has no meaningful effect on the long-range order parameter. The transformation of the disordered solid solution developed by MA to ordered Fe - Al - ( B ) intermetallics was a consequence of sintering. Also, the nano-scale structure of the samples was retained even after sintering. The microhardness of pore-free zones of the nanostructured specimens decreased by increasing the sintering temperature. Moreover, the sintering temperature has no effect on the compressive yield stress. However, the fracture strain increased by increasing the sintering temperature. The samples containing 1 at.% B showed more strain to fracture compared with the B -free and 5 at.% B samples.

Role of Chemical Ordering on Phononic Transport in Binary Alloys

Many random substitutional solid solutions (alloys) will display a tendency to chemically order given the appropriate kinetic and thermodynamic conditions. Such order-disorder transitions will result in major crystallographic reconfigurations, where the atomic basis, symmetry, and periodicity of the alloy change dramatically. Consequently, phonon behavior in these alloys will vary greatly depending on the type and degree of ordering achieved. To investigate these phenomena, the role of the order-disorder transition on phononic transport properties of Lennard-Jones type binary alloys is explored via non-equilibrium molecular dynamics simulations. Particular attention is paid to regimes in which the alloy is only partially ordered. It is shown that, through exploitation of the long-range order parameter, thermal conductivity of binary alloys can be effectively tuned across half an order of magnitude at low-to-moderate temperatures.

Long-range Order Parameter Determination by Convergent Beam Electron Diffraction

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.