A.M. Mebed

Effect of phase fraction on the tri-junction in two-phase nanoparticle systems

Abstract The equilibrium dihedral angles at the solid–solid–vapor tri-junctions of two-phase Cu–Ag alloy nanoparticles 40–100 nm in diameter were measured as a function of phase fraction using transmission electron microscopy. The {111} solid–solid interface was cusp-oriented while the surface orientations of the Cu-rich and Ag-rich phases at the tri-junction were mostly free to vary. The dihedral angles at the tri-junction were found to vary with the phase fraction, due to the coupling between the relative amounts of each phase and the equilibrium conditions at the tri-junction. This equilibrium condition was used to measure the ratio of the Ag-rich and Cu-rich surface energies to the {111} interfacial energy, which were found as 2.1 and 3.5, respectively.

Thermal analysis study for the phase determination and instable to metastable transformation of the Co–13Cu alloy

The differential thermal analysis (DTA) is utilized to determine the phase boundary and phase equilibria of Co–Cu alloy having a miscibility gap. Regions for various phase i.e., spinodal and coherent binodal, peritectic, magnetic and the transformation from the two phases to α phase transformations are distinctly determined for the Co–13 at%Cu alloy. The obtained results might indicate the continuity of the decomposition kinetics at the boundary between instable and the metastable regions but an activation barrier is needed. The activation energy for the magnetic transformation is determined to be 182.2 ± 2.1 kJ mol−1.

Computer simulation of A2/B2 second-order phase transition based upon the Khachaturyan diffusion equation

A computer simulation, based on the Khachaturyan diffusion equation, is presented to develop the kinetics of the morphological evolution of the A2/B2 second-order phase transition in a binary solid solution. The evolution of the occupation probability, as a function of composition, shows a good similarity to the actual micrographs experimentally obtained based on the macroscopic composition gradient method. These results are used in parallel with the results of the evolution of the long-range order parameter as a function of the ageing time, to verify a new concept of the ordering behaviour inside the ordered phase.

Computational and experimental study of the effect of the composition on the morphology of the ordered domains and APBs structures

Abstract The formation and growth of ordered domains in Fe–Al alloys is explored computationally in two-dimensions (2D) using the modified Khachaturyan diffusion equation by utilizing the thermodynamic parameters related to the equilibrium phase diagram and experimentally by using a single sample containing a steep composition gradient. The effect of alloy composition on the morphology of the ordered domains as well as the APBs in a single phase is presented. Experiment and computer simulations show that the time to form an ordered structure increases rapidly as the composition approaches the order–disorder transition line. Moreover, diffuse APBs are found to be formed near the transition line. The early stage of ordering is also described.

Composition, microstructure, Vickers hardness and activation energies of Co–Cu alloys fabricated by arc melting technique

We have determined the phase transition for the Co-20 and -30 at.% Cu alloys fabricated by arc melting technique, from the binodal to the two phases α + L as well as the peritectic transitions, using differential thermal analysis (DTA). We equally studied the effects of aging treatment, ranging from 3 to 35 h, on the alloy samples using scanning electron microscopy (SEM) and Vickers hardness (HV). The activation energies of these alloys are equally determined using five established models. Our results show that for aging time up to 15 h, within the spinodal region at 773 K, the hardness value for Co-20 and -30 at.% Cu alloys oscillates reaching a local maximum at the aging time of 8.5 ± 0.5 h. After 20 h of heat treatment, the HV for Co-20 at.% Cu alloy diminishes significantly while that of Co-30 at.% Cu effectively stabilizes at 241 MPa. The activation energies for the peritectic transformation based on Ozawa model are estimated to be 2465 and 2680 kJ mol−1 for Co-20 and -30 at.% Cu, respectively. †On leave for: Al-Jouf University, Skaka-2014, KSA.

Crystallography and Computer Simulation of Heat Treated Co- 10 at. Pct. Cu Alloys

The influence of heat treatment on phase decomposition of Co-10 at. pct. Cu alloy was studied. The materials and phase compositions were studied by using energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) techniques. XRD analysis showed that the samples contained Co, Cu, CuO and CoCu2O3 phases depending on the heat treatment regimes. Moreover it is found that the formation of dendrite Co phase render the spinodal decomposition even for deep long aging inside the miscibility gap. The crystal structural parameters were refined with FULLPROF program. 2-D computer simulation indicates that the morphology and the shape of the microstructure agree with experimental SEM micrographs for the Cu rich phase.

Thermal properties of pure and doped lithium-ammonium sulphate single crystals

Abstract The thermal diffusivity α of pure lithium-ammonium sulphate (LAS) crystals is measured along the three crystallographic directions in the temperature range 300–500 K using the plane temperature wave technique. The effect of doping LAS crystals with some divalent metal ions on the temperature dependence of α in both the ferroelectric and paraelectric phases is discussed. The average length of the distorted regions formed by the dopant in the lattice of LAS is calculated. The thermal conductivity of LAS crystals is calculated in the same temperature range. The phonon mean free path in both the ferroelectric and paraelectric phases is estimated and the results are discussed in the light of the difference between the ionic radii and the concentrations of the dopant ions in LAS.