The thermodynamics of PdAgH ternary solid solutions

The solubility of hydrogen in PdAgH ternary solutions in equilibrium with H₂ gas at atmospheric pressure has been measured in the temperature range 625–1111 K and in PdAg “binary solvents” containing up to 93 at.% of Ag. Concomitant elastic measurements have provided data which enable the partial thermodynamic functions of the H-atoms deduced from the solubility measurements to be converted so as to refer to a hypothetical PdAg lattice of constant specific volume. The resulting “volume corrected” functions have been discussed in terms of the cell model for ternary solutions and have been shown to vary with temperature and Ag-concentration in a manner in accord with this model.     

The diffusivity of hydrogen in PdAgH ternary solid solutions

An electrolytic double-cell system has been used to determine the variation of the diffusivity of hydrogen through PdAg membranes as a function of temperature in the range 280–333 K and Ag-composition in the range 0–30 at.%. The experimental diffusivities have been analyzed in terms of the cell theory of interstitial solid solutions. At a given temperature the hydrogen diffusivity shows an initial small increase with increasing Ag-concentration. This is due to lattice dilation effects. As the Ag-concentration increases beyond 0.05 at.%, the H-diffusivity decreases due to the generation of trapping sites for H-atoms.     

Thermodynamics of CoBH ternary solid solutions

Solubility isobars for H in CoB binary solvents containing up to 0.1 at.% B have been determined in the temperature range 920–1430 K. The solubility data yield values for the partial molar thermodynamic functions of the dissolved H-atoms which manifest a strong long-range HB repulsive interactions.     

The diffusion of hydrogen at low temperatures in PdErH ternary solutions

An electrolytic technique has been used to measure the temperature variation of the diffusivity of hydrogen in PdEr solid solutions containing up to 8 at.% Er. The diffusivities were measured in the temperature range 270–340 K. The diffusion data for a given PdEr binary solvent conform to the Arrhenius representation. However the apparent activation energies Q_a exhibit a non-linear variation with Er content. The Q_a value show an initial increase with Er content and then a decrease after a maximum at ∼ 5 at.% Er. This behavior has been interpreted in terms of a statistical model based upon classical jump theory.     

Anomalous strain rate dependence of the serrated flow in NiH and NiCH alloys

Serrated flow in NiH, NiCH, and NiC alloys was studied over a wide range of temperature and strain rates. The results for C related serrated flow in NiC or NiCH alloys were in excellent agreement with previous results and were consistent with dislocation pinning by C solutes at the dislocation cores. Hydrogen related serrated yielding was observed in NiH and NiHC alloys. Solute C had only a small effect on the temperature range of this H related serrated flow. The results could be interpreted on the basis of hydride formation at the dislocation cores and diffusion of H in these hydrides.     

The γ-phase regions of the CuZn,NiZn and Pd-Zn binary systems

The γ-phase regions of the CuZn, NiZn and PdZn binary systems are discussed in the light of recently published studies of inversion anti-phase domain (IAPD) superstructures in the first two of these systems and with regard to the short-range-order phenomena observed in a number of γ-phase alloys. New X-ray and electron diffraction evidence for the existence of the IAPD structures in a Pd-75 at.% Zn alloy is presented. Finally, it is suggested that the currently accepted Ni-Zn and Pd-Zn equilibrium phase diagrams be modified to show only a single γ-phase field. This would provide a consistent representation of the phenomena occurring in the γ-phase region of both these and the CuZn binary systems.     

A study of phase decomposition in CuNiFe alloys

A study of phase decomposition in two CuNiFe alloys was realized by AP-FIM. It was possible to confirm that phase decomposition takes place via spinodal decomposition in this alloy system, as the amplitude of the composition modulation increased with ageing time without practically any change in the wavelength of the modulation. It was also observed that the morphology of the decomposed phases is related to the coherency-strain energy as predicted by Cahn's theory of spinodal decomposition. By analysis of the data of the modulation wavelength, it was possible to estimate the coherent spinodal temperature to be 800 ± 25 and 900 ± 25 K in Cu46 at.% Ni4 at.% Fe and Cu48 at.% Ni8 at.% Fe alloys, respectively. In the early stage of decomposition, the change in modulation wavelength showed a time exponent as small as about 0.07. On the other hand, in the coarsening stage the change in the modulation wavelength agreed well with the LSW theory of thermally activated growth. The activation energy for this coarsening process was determined to be 216 ± 10 and 232 ± 10 kJ/mol in the Cu46 at.% Ni4 at.% Fe and Cu8 at.% Fe alloys, respectively. The compositions of the decomposed phases are consistent with the miscibility gap in the calculatedequilibrium CuNiFe phase diagram.     

Kinetics of leaching of a low-grade FeNiCuCo matte in ferric sulphate solution

A study of the dissolution of a low-grade FeNiCuCo matte in acid ferric sulphate solution is reported. This matte contained a number of different phases, and a detailed quantitative mineralogical analysis of the matte was used as a basis for mathematical modelling of the leaching process. The mathematical model assumed that the matte particles were leached by a shrinking-particle mechanism, and that the surface reaction was rate-limiting and electrochemical in nature. The experimental results verified these assumptions, and showed that the redox potential of the solution best approximated the potential of a matte particle during leaching.     

The structure of twins in FeNi martensite

This paper corrects an error in a previous paper by Déchamps and Brown and presents a much improved model for the structure of twins in FeNi martensite. The model is based upon the dissociation of screw dislocations under the stress due to the martensitic transformation.     

Residual resistivity during clustering in AlZn solid solutions

In the alloys Al 8 to 25 wt,% Zn, the isothermal kinetics of clustering has been followed at different ageing temperatures by resistivity measurements. At low temperatures, the classical “anomaly” (increase, maximum and decrease) is observed. It is associated with a large density (~10¹⁹ cm⁻³) of Zn clusters of 1–2 nm of diameter. The resistivity kinetics have been calculated with the help of Hillel's diffraction model and of transmission electron microscopy and neutron small-angle-scattering structural results: the experimental behaviour is fairly well reproduced. At high ageing temperatures, a metastable state sets during an incubation period of clustering and the corresponding resistivity plateau is higher for lower temperature. A binding energy between zinc atoms of 0.04 eV has been deduced from a simulation of the equilibrium between clusters containing less than 5 atoms. At intermediate temperatures, the behaviour is composite and is not fully understood.     

A determination of interfacial energy and interfacial composition in CuPb and CuPbX alloys by solid state wetting measurements

Solid state wetting studies have been used to measure interfacial energies and also to estimate interfacial composition. The approach is applicable to systems where one phase forms partially wetting islands on a substrate of the other phase, and requires that the compositions of all surfaces be carefully monitored so as to allow surface energies to be corrected for adsorption effects. The CuPb interface was studied by this technique with the wetting of Pb islands on polycrystalline Cu, CuAg and CuAu polycrystalline alloys. The results show that Au lowers the CuPb interfacial energy, indicating the presence of Au segregation at the interface, whereas Ag does not change the interfacial energy. Both of the above results are also correctly predicted, quanlitatively, by a simple nearest neighbor bond model used in conjunction with the regular solution approximation. Studies of Pb on monocrystalline (001)- and (111)-oriented substrates of Cu have been carried out. These yield values of 926 and 1016 mJ/m² for the two interfacial energies, respectively. Similar studies of Pb on (001)Cu-5 at.% Au, and (111)Cu-8 at.% Au yield interfacial energies of 889 and 959 mJ/m², respectively, indicating interfacial excesses of Au of 0.22 and 0.34 monolayers at those interfaces.     

On the formation of 2H stacking sequence in 18R martensite plates in a precipitate containing CuAlNiTiMn alloy

Basal planes stacking sequence variation in M18R martensite of CuAlNiTiMn alloy have been studied by means of electron diffraction and lattice imaging. Samples subjected to two different homogenisation temperatures (1173 and 973K) and two different cooling rates—water quenched and air cooled were analysed. The observed changes in stacking sequence have been attributed mainly to stress accomodation around X_L and X_S precipitates. Very small X_SS precipitates of the same phase have been observed and their high influence on the stacking sequence of martensite plates have been explained by means of a new “dislocation” mechanism related to their coherency loss into the matrix.