Amer Bashir Ziya

Resistometric evidence of short-range order formation in the ternary Au40Ag40Pd20 alloy

Abstract Short-range order (SRO)-induced electrical resistivity changes were measured in the Au 40 Ag 40 Pd 20 (at.%) alloy during isochronal annealing experiments. Isochronal annealing after quenching from high temperatures showed that SRO-formation in these alloys leads to an increase in electrical resistivity. From the observation of linearity in the resistivity versus T a −1 curves and from a comparison with theory, it is concluded that the resistivity changes in these alloys are proportional to the changes of the effective SRO-parameter for the first co-ordination shell.

The kinetics of vacancy annihilation in the ternary Au25Ag25Pd50 alloy

Abstract The behavior of vacancies was investigated in the ternary Au 25 Ag 25 Pd 50 alloy with the help of electrical resistivity measurements during various isothermal-annealing experiments. The relaxation times of vacancies and short-range order (SRO) formation under the influence of thermal and quenched-in vacancies were determined. It was found out that the life times of vacancies were comparable to the relaxation times of SRO formation. The results show that vacancy annihilation follows first order kinetics. Further, the activation enthalpies for vacancy annihilation, formation, migration and self-diffusion were determined from the relaxation times. The values of the determined parameters were found to be self-consistent and agreed quite well with the values predicted by the theory.

The enhanced range of temperature for coefficient of low thermal expansion, electrical and thermal conductivities of Cu substituted Fe–Ni invar alloys

Six alloys of Fe65Ni35−x Cu x (x = 0, 0.2, 0.6, 1, 1.4, 1.8 at.%) have been prepared by conventional arc-melting technique and characterized by utilizing high temperature x-ray diffraction (HTXRD) technique at a range from room temperature to 773 K for determination of phase, lattice parameter (a), coefficient of thermal expansion (α(T)), mean square amplitude of vibration ( characteristic Debye temperature (ΘD), electrical resistivity (ρ) and thermal conductivity (κ). The studies showed that these alloys form face centered cubic structure (fcc) throughout the investigated temperature range. The values of α(T) were found to be comparable to those for conventional Fe–Ni invar alloys but have increased temperature span to a significant extent. The mean square amplitude of vibration ( and Debye temperature were found to remain almost unchanged in the invar temperature range, whereas the electrical and thermal conductivity were found to improve.

A study of the structure and thermal parameters of Ni88.6Cr11.4 alloy

The structure and thermal parameters of the alloy Ni88.6Cr11.4 have been studied by an in-situ x-ray diffraction technique. The experiments show that the alloy has a single phase with fcc (A1) structure, the phase boundary of which extends beyond 1050 K. No evidence of the formation of ordered structures was found. The temperature factor was found to be independent of the static displacements. The mean linear thermal expansion does not follow the classical Gruneisen relationship. Further, the addition of Cr into Ni leads to an increase in the value of the characteristic Debye temperature ΘD, whereas a minor effect is observed in the coefficient of linear thermal expansion α(T) of the alloy. The results are in good agreement with those in the literature for other compositions of Ni–Cr alloys.

Effect of Additional 3d Elements M (M = Fe and Ni) on Atomic Ordered Structure in Cu-M-Pd alloy

X-ray diffraction measurements were performed to elucidate the effect of ternary addition of Fe and Ni elements to Cu-rich Cu-Pd binary alloy system on the structure and an atomic ordering. Xray polycrystalline diffraction patterns of the specimens quenched from 900oC have shown that a single phase with face-centered cubic (fcc) structure is formed in all the specimens for Ni system and in specimens with Pd composition xPd (at. %) more than 10 for Fe system. After appropriate heat treatment, the Fe system with a fcc single phase forms fcc-based Cu3Au-type ordered structure for xPd around 20, and body-centered-cubic based CsCl-type ordered structure for xPd around 40. Assuming that Fe atoms simply substitute for Cu atoms in the ordered structures, the atomic phase coincides well with that of Cu-Pd alloys for the Cu3Au-type structure, but there is a discrepancy for the CsCl-type structure on that it does not appear as a single phase in Cu-Fe-Pd alloys. As for Ni system, no ordered structures are formed except for the alloys with xPd more than 35, in which fcc and CsCl-type structures are found to coexist.

THERMAL DIFFUSE SCATTERING IN SOME FCC ALLOYS

Thermal diffuse scattering (TDS) intensity has been calculated for some fcc alloys. The effects of variation of temperature and atomic concentration on TDS have been studied. A systematic change in TDS is observed for various atomic concentrations and temperatures.