Grain boundary deformation in Cd-Zn and Zn-Al alloys

Activation energies for creep have been measured on fine-grained and coarse-grained specimens of pure cadmium, zinc, and Cd-Zn and Zn-Al alloys in the temperature range (0·4–0·8)T _m. It is found that in the case of fine-grained specimens the activation energies for creep are equal to the activation energies for grain boundary diffusion in cadmium and zinc, and in the case of coarse-grained specimens — to that of volume self-diffusion.     

Transient creep during transformation in Cd-Zn alloys

Transient creep of Cd-2 wt. % Zn and Cd-17·4 wt. % Zn alloys has been studied under different constant stresses ranging from 6·4 MPa to 12·7 MPa near the transformation temperature. The results of both compositions showed two transient deformation regions, the low temperature region (below 483 K) and the high temperature region (above 483 K). From the transient creep described by the equation _tr=Bt ⁿ, where _tr andt are the transient creep strain and time. The parametersB andn were calculated. The parameterB was found to change with the applied stress from 0·3×10^–4 to 3×10^–4 and from 0·6×10^–4 to 18×10^–4 for Cd-2 wt. % Zn and Cd-17·4 wt. % Zn, respectively. The exponentn was found to change from 0·8 to 0·95 for both alloys. The parameterB was related to the steady state creep rate through the equation , the exponent was found to be 0·5 for Cd-2 wt. % Zn and 0·6 for the eutectic composition. The activation energies of transient creep in the vicinity of the transformation regions (above 483 K) were found to be 50·2 kJ/mole for Cd-2 wt. % Zn and 104·7 kJ/mole for the eutectic composition characterizing the mechanisms of grain boundary diffusion and volume diffusion in Cd, respectively.     

Steady state creep during transformation in Cd-Zn alloys

Apparent steady-state creep of Cd-2 wt. % Zn and Cd-17·4 wt. %Zn alloys has been studied under different constant stresses ranging from 6·4 MPa to 12·7 MPa, near the transformation temperature of 483 K. The strain rate of the steady-state creep for both compositions has shown two temperature regions of deformation, the low-temperature region (below 483 K) and the high-temperature region above this temperature. The stress exponent m' was found to change from 4·7 to 2 for Cd-2 wt. % Zn and from 3·1 to 2·4 for Cd-17·4 wt. % Zn alloys. The activation energies in the temperature region below the transformation temperature have been found to be 84 kJ/mole for Cd-2 wt. % Zn and 70 kJ/mole for Cd-17·4 wt. % Zn alloys characterizing the mechanism of volume self-diffusion in Cd.     

Resistivity changes in cold-worked Cd-Ag and Cd-Zn

Polycrystalline wires of Cd-0.3 at. %Ag, Cd-1.0 at. % Ag, Cd-3.3 at. % Ag and Cd-0.1 at. % Zn, Cd-0.5 at. % Zn, Cd-2.6 at. % Zn were deformed by torsion in liquid nitrogen. Up to 200 K their isochronous annealing spectrum of electrical resistivity reveals the same main features (i.e. annealing stages C1, C2 and C3) as that of pure Cd and of dilute alloys Cd-Mg and Cd-Sn. The position of the annealing stages is insensitive to the type and amount of impurity and the degree of deformation. The gradual diminution of stage C3 with increasing Ag content is ascribed either to a dislocation mechanism or a disappearance of point defects by short range migration.We wish to express our thanks to Dr. P.Luká and Dr. I.Stulíková (Charles University, Prague) for stimulating discussions and valuable comments.     

Microstructure evolution of undercooled Fe-Co-Cu alloys

Rapid solidification of undercooled Fe-Co-Cu alloys was investigated by means of fluxing purification and cyclic superheating technique. A transition in microstructure from dendrites to phase-separation occurred above a phase-separation undercooling ΔT_sep. When ΔT<ΔT_sep, dendrite was observed, the trunks were rich in Fe and Co, while Cu was rich at inter-dendrites. However, the phase-separated microstructure was obtained once ΔT>ΔT_sep, with a large sphere of L1 phase located almost at the center of the sample and enwrapped by L2 phase. ΔT_sep was 222, 88 and 45 K for Fe₅₀Co₃₀Cu₂₀, Fe₂₅Co₂₅Cu₅₀ and Fe₁₅Co₁₅Cu₇₀ alloys in this work, respectively. It was investigated that L1 phase solidified before L2 phase after liquid separation and followed different ways.     

Concentration dependence of nickel diffusion in nickel-cobalt alloys

In the present paper the results of measuring the self-diffusion coefficients for Ni in Ni-Co alloy in the composition interval 0–100 at.% Co, and in the temperature range 1065–1290 °C are given. The measurements have been carried out by the Gruzin method using the radioisotope Ni-63. The curves indicating the concentration dependence of the diffusion coefficients calculated for differentaT _m vaules (T _m is the melting point at a given concentration,a is a number from the interval (0, 1)) are straight lines; this feature has been found in other solid solutions which slightly deviate from regularity as well. It results in simple equations for the concentration dependence of self-diffusion characteristicsD ₀ andH.     

The pressure dependence of resistivity in amorphous copper-zirconium alloys

The variation of electrical resistance with hydrostatic pressure has been measured at room temperature for a number of amorphous Cu-Zr alloys. In each case the resistance falls to a lower value so that the volume dependence of resistance is positive. No correlation is found with the thermoelectric power of these materials and, in a detailed analysis, it is argue that for such transition metal alloys, such a simple correlation is most unlikely.     

The pressure and temperature dependence of electron energy-gaps in semiconductor alloys

The pressure and temperature dependences of the direct energy gaps of semiconductor alloys are calculated using the theory of energy gap bowing of Hill. No adjustable parameters are used, and the pressure and temperature coefficients of the bowing parameter are related to the bulk compressibilities and thermal expansion coefficients respectively. The agreement with the rather small number of experimental results is quite good.The non-linear composition dependence of the pressure coefficients of semiconductor alloys suggests that there are inconsistencies in present formulations of dielectric model theories of alloys.     

Temperature dependence of thermoelegtromotive force and Nernst-Ettingshausen effect in nickel-cobalt alloys

The thermoelectromotive force and the Nernst-Ettingshausen effect for alloys of the nickel-cobalt system within the range of temperatures from room temperature to 500°C are examined in the present work. The dependence was investigated of true Nernst-Ettings-hausen constant and of thermoelectromotive force on the percentage of cobalt content in the nickel-cobalt alloys at various temperatures. The comparison of data obtained In studying the temperature dependence of the true Nernst-Ettingshausen constant Q_i and of the electrical resistivity with the theory, has indicated that Q_i is connected with electrical resistivity and temperature in the equation proposed by Kondorskii; Q_i=–( + )TTranslated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 43–46, June, 1972.In conclusion the authors express their gratitude to Professor E. I. Kondorskii for his interest in the study, and for discussion of the results obtained.     

The temperature dependence of magnetization of Gd-Tb alloys

It is shown that a mean field theory can describe very closely the variation of magnetization with temperature found in a series of Gd-Tb alloys. The proportionality of the exchange constants to the density of the states at the Fermi energy has been confirmed. The values for the densities of states for Gd and Tb required for satisfactory fitting of the experimental results are in agreement with values calculated from electronic specific heat measurements.     

Mechanism of stress dependence of saturation magnetostriction in amorphous alloys

The phenomenological theory of stress dependence of saturation magnetostriction in amorphous alloys has been developed. Two models of magnetostriction have been considered: the pair-ordering model and the random anisotropy model. The stress dependent magnetostriction is shown to be related to microstructural parameters of amorphous alloys. It has been concluded that recently performed experiments have confirmed theoretical predictions.     

Concentration dependence of the Kondo exponent in heavy fermion alloys

The diluted Anderson model is studied, in which a fraction c of sites have a strongly correlated f-orbital. The two-band version of the Gutzwiller method is used to describe the ground state. As c varies from 0 to 1, the Kondo exponent gradually decreases from the single ion value to the lattice value derived by Rice and Ueda.     

Compositional dependence of positron annihilation in HgTl alloys

Ratios of coincidence counting rates of annihilation gammas at 0 and 10 milliradians for 13 atomic concentrations from 0 to 50% of thallium in liquid mercury were measured. A sharp discontinuity at about 5% of thallium indicates an abrupt change of cluster size and concentration, which may be related to the peaking of electric thermopower of the alloy.     

Concentration dependence of short-range order parameters in annealed copper-aluminum alloys

The method of diffuse X-ray scattering was used to investigate -CuAl alloys containing between 11.9 and 17.6 at.% aluminum after prolonged stepwise annealing. Analysis of the short-range order coefficients indicated uniform ordering at concentrations up to 15 at.% aluminum and possible departure from uniform ordering in alloys with higher concentrations. It was shown that the structure of the ordered alloy is consistent with the model proposed by Gehlen and Cohen [13].     

Temperature dependence of forced volume magnetostriction in fcc Fe-Ni alloys

The forced volume magnetostriction of the fcc Fe-Ni Invar alloys has been measured in the temperature range from 77 to 900 K to elucidate the magnetovolume effect at finite temperatures. The temperature dependence of (θ ω/θ(H/M) is evaluated as well as (θ ω/θH), where ω is the volume expansion. These results are discussed using a phenomenological model for the magnetovolume effect which takes into account the contribution of the correlation between local magnetic moments.