Z. M. Farid

Investigation of the Behaviour of Structural Changes during Recovery of Crystal Defects in Plastically Deformed Fe–50% Ni Alloy by Magnetic Measurements

Isochronal and isothermal annealing experiments in the temperature range 25 to 900 °C revealed the existence of different annealing stages in the annealing spectrum of plastically deformed Fe-50% Ni alloy by observing the associated changes in maximum magnetic permeability (μ max ) and magnetic coercivity (H er) . On annealing, a first stage centered around 225 °C appears, activated by (1.16 ± 0.02) eV which is explained on the basis of an increase in local order in the alloy matrix. A second stage in the temperature range 550 to 750 °C arises because of the dissociation of defect clusters, activated by (1.8 ± 0.1) eV. The third recovery stage appears above 750 °C, activated by (3.06 ± 0.02) eV, and the process is related to the climb motion of dislocations during the recrystallization process. Changes in initial lattice defect concentration were found to have influence on the amplitude and the position of the different observed stages. The kinetics of FeNi 3 precipitation observed at high temperatures (T a ≥ 800 °C) are discussed.

The effect of lattice disorders on domain wall-dislocation interaction in Ni-5wt% Mn alloy

The behaviour of domain wall-dislocation interaction in Ni-5wt% Mn alloy has been investigated in pre-annealed, quenched and γ-irradiated samples using some magnetic structure-sensitive properties. In all three samples it was found that the initial magnetic susceptibility, χa, and the maximum magnetic susceptibility, χmax, were increased with the degree of plastic strain, and attributed to the formation of loops of domain wall around dislocations during the early stage of deformation. Further increase in dislocation density in the matrix during the later stage of deformation, affects the average value of the strength of interaction between the domain wall and dislocation, thus contributes to the decrease in χa and χmax. The observed changes in the magnetic anisotropy,K, with plastic strain deformation is explained in terms of the magnetic hardening of the material by dislocations. Excess quenched vacancies and their clusters had an observable effect on domain wall-dislocation interaction, which is assumed to be due to the expected interaction and their pinning action that appear in the field of the nickel matrix.

On two types of creep behaviour of CuZn solid solution

Abstract The stress and temperature dependence of steady state creep rate is investigated for Cu-30%Zn and Cu-10%Zn alloys under stresses of 15–40 kg mm−2 in the temperature range 200–325°C. The existence of a critical stress σc (T), which separates two types of behaviour characterized by a sensitivity parameter m′ close to three at low stresses and m′ > 6 for higher stresses, has been observed. It is thought that a change occurs in the mechanism which controls the creep rate. Also the investigation of transient creep gives evidence of two types of creep behaviour. It is shown that the creep of α-brasses can be described as a viscous glide of dislocations at low stresses. The shear mechanism owing to the slip of dislocation along shear planes is the mechanism controlling the creep rate at higher stresses. Zinc concentration seemed to be ineffective on the mechanisms controlling the creep rate. The values of apparent activation energy, namely 39.3 kcal mol−1 and 33.4 kcal mol−1 for Cu-10%Zn and Cu-30%Zn alloys respectively, show that the creep is controlled by self-diffusion.

On the grain boundary internal friction peak of α-brasses

Abstract A conventional Ke pendulum was used to investigate the temperature dependence of internal friction for thoroughly annealed samples of Cu30wt.%.Zn. The relaxation peak observed at 300 °C at a vibration frequency of 0.60 Hz was attributed to grain boundary diffusion. The energy activating the process was 1.84 eV and characterized the activation energy for self-diffusion in copper. The relaxation strength showed a strain amplitude dependence, but the activation energy and peak temperature did not. The effects of solute atom concentration, cold work and quenching were also tested.