I. M. Ghauri

Effects of neutron irradiation on the stress relaxation rate in Al–Cu–Mg alloy

Neutron irradiation effects on the stress relaxation rate of Al–Cu–Mg alloy have been investigated. The specimens were exposed to 100 mC, Ra–Be neutron source of continuous energy 2–12 MeV for a period ranging from 4 to 16 days. Stress relaxation tests during the tensile tests at room temperature were performed at multiple stress levels up to the fracture using a universal testing machine. The comparison of the stress relaxation rate of irradiated specimens with that of an unirradiated one shows that the rate decreases after irradiation. The decrease becomes more pronounced as the exposure time increases. The activation energy to the movement of dislocations was found to be higher in irradiated specimens than in an unirradiated one. The analysis of results shows that the rate controlling process of stress relaxation in irradiated specimens is different from that of an unirradiated one. The micrographs of fractured surfaces in fact point to the changes that take place in the fracture mechanism before and after irradiation. These observations account for the decrease in the stress relaxation rate.

Rate controlling process of stress relaxation in high purity irradiated titanium

The stress relaxation rate in irradiated high purity polycrystalline titanium was studied at room temperature. Titanium specimens of grain size 40 µm were irradiated with 18 MeV electrons for 12 min at 300 K to a dose of 0.01 dpa. The stress relaxation rate in the specimens was studied using a universal testing machine. The comparison of irradiated samples with un-irradiated ones, annealed and tested in similar conditions, revealed that the stress relaxation rate is lower in the irradiated titanium specimens than in the un-irradiated ones. The results are analysed in terms of a single barrier model of stress relaxation. The intrinsic height of the energy barrier to the movement of dislocations was found to be higher in the case of irradiated specimens than in the un-irradiated ones. This is attributed to the local pinning of dislocations with the irradiation induced defects acting as obstacles.

Tensile behavior of post-irradiation annealed Cu–Ni alloy

The present paper investigates the tensile properties of post-irradiation annealed Cu–Ni alloy. The specimens were irradiated with a 15 MeV electron beam at room temperature and the post-irradiation annealing (PIA) of the specimens was carried out under vacuum at 450 °C for 15–120 min. The yield stress (YS), ultimate tensile stress (UTS), percentage elongation, stress relaxation rate and activation volume of both as-irradiated and post-irradiation annealed specimens were examined at room temperature using a universal testing machine. The results show that PIA of the specimen at 450 °C for 15 min decreases its YS and UTS, whereas the percentage elongation is increased. The changes in the tensile parameters become more pronounced with increases in annealing time. Effects of PIA on the stress relaxation rate and activation volume indicate that the relaxation rate of post-irradiation annealed specimens increases, and the activation volume decreases, with an increase in annealing time.

Irradiation energy dependence of stress relaxation rate and activation volume in polycrystalline nickel

Stress relaxation in un-irradiated and electron beam irradiated polycrystalline nickel (99.99%) was studied at room temperature. The specimens were irradiated by high-energy electrons with energies in the range 8–18 MeV for 12 min at 300 K. The tensile tests of both un-irradiated and irradiated specimens were carried out at room temperature using a universal testing machine. During deformation, straining was frequently interrupted to observe stress relaxation at fixed loads. Measurements were made over the entire stress-strain curves up to fracture. The stress-relaxation was found to be logarithmic with time and its rate was found to decrease with an increase in the energy of incident electrons. The activation volume Vσ was observed to decrease with an increase in stress levels (σ0) both in un-irradiated and irradiated specimens, however Vσ values were higher in irradiated specimens than those of un-irradiated specimens. The intrinsic height of energy barrier (Uo) to the movement of dislocations increased with an increase in incident electron energy. The results are analysed in terms of a single barrier model of stress relaxation proposed by Feltham.

A STUDY OF STRESS RELAXATION RATE IN UN-IRRADIATED AND NEUTRON-IRRADIATED STAINLESS STEEL

Stress relaxation rate in un-irradiated and neutron-irradiated 303 stainless steel was investigated at room temperature. The specimens were exposed to 100 mC, Ra-Be neutron source of continuous energy 2–12 MeV for a period ranging from 4 to 16 days. The tensile deformation of the specimens was carried out using a Universal Testing Machine at 300 K. During the deformation, straining was frequently interrupted by arresting the cross head to observe stress relaxation at fixed load. Stress relaxation rate, s, was found to be stress dependent i.e. it increased with increasing stress levels σ0 both in un-irradiated and irradiated specimens, however the rate was lower in irradiated specimens than those of un-irradiated ones. A further decrease in s was observed with increase in exposure time. The experiential decrease in the relaxation rate in irradiated specimens is ascribed to strong interaction of glide dislocations with radiation induced defects. The activation energy for the movement of dislocations was found to be higher in irradiated specimens as compared with the un-irradiated ones.

A COMPARATIVE STUDY OF STRESS RELAXATION RATE IN UNIRRADIATED AND IRRADIATED PURE TITANIUM AT LOW TEMPERATURES

Stress relaxation rate in unirradiated and electron-beam-irradiated polycrystalline titanium (99.994%) was studied in the temperature range 300–100 K. Titanium specimens were irradiated with 12 MeV electrons to a dose of 0.01 dpa for 12 min. at 300 K. Tensile tests of the specimens were performed using a Universal Testing Machine in the given temperature range. To measure the relaxation of stress with time, the crosshead of the machine was arrested at different fixed loads. Stress relaxation rate s for a given stress level σ0 was found to be temperature dependent, i.e., it decreased with decreasing temperature both in unirradiated and irradiated specimens. However, the decrease was more pronounced in irradiated specimens than that of unirradiated ones. The observed decrease in s values with decrease in temperature is ascribed to the retarding effect of unrelaxed dislocations pinned at defects, especially at the twin boundaries in the course of deformation, which became more conspicuous in irradiated speci...

A STUDY OF MICROSTRUCTURE AND TENSILE PROPERTIES OF PROTON BEAM IRRADIATED Al-Mg-Si ALLOY

In the present paper, the microstructure and tensile properties of Al–Mg–Si alloy irradiated with 2 MeV protons for 5, 10, 20, and 40 mins at 300 K are investigated. The microstructure of irradiated specimens, observed using metallurgical microscope, shows that aspirates are emitted out from the surface of irradiated specimens, which take the form of clusters and/or precipitates with increase of exposure time. The tensile behavior of irradiated specimens was investigated using universal testing machine and compared with that of unirradiated one. The yield stress, ultimate tensile stress and % elongations remain unchanged after 5 and 10 mins of irradiation. However with an increase of irradiation time up to 20 mins, an increase in yield stress, ultimate tensile stress and decrease in % elongation was observed. With further increase of exposure time to 40 mins, the increase in yield stress and decrease in plasticity became more prominent. The results of stress relaxation tests performed during the tensile d...

STRESS RELAXATION BEHAVIOR OF IRRADIATED COPPER IN THE TEMPERATURE RANGE 150–300 K

The present study reports the stress relaxation behavior of irradiated polycrystalline 5N copper deformed in the temperature range 150 to 300 K. The wire specimens were exposed to an 18 MeV electron beam at room temperature and stress relaxation tests of the specimens were carried out during the tensile test, using universal testing machine between 150 to 300 K. Stress relaxation rate of the specimens was found to decrease with the decrease of test temperature. The decrease of the stress relaxation rate with temperature in irradiated specimens is attributed to the dislocation-defects interaction, which is more pronounced at low temperature due to the reduction in available thermal energy necessary for the relaxation of dislocations.

DC CONDUCTION MECHANISMS IN Al–SnO2–Al STRUCTURE DEPOSITED BY THERMAL EVAPORATION

The DC conduction mechanisms in metal–insulator–metal sandwich structure based on amorphous thin films of SnO2 have been studied in the thickness range 100–400 nm, in the substrate temperature range 293–543 K, and in the annealing temperature range 473–773 K, and the results are discussed in terms of current theory. It is observed that at low field and low temperature the conduction mechanism is found to obey the hopping model, at higher temperature the conduction takes place by transport in the extended states but at high field the main barrier lowering effect is associated with localized centers. The increase in electrical conductivity with film thickness is caused by the oxygen vacancies and

IRRADIATION EFFECTS ON MICROSTRUCTURE AND TENSILE BEHAVIOR OF POLYCRYSTALLINE NICKEL

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