Defects In Nickel Research Articles

A study of the radiational defects in nickel after implantation of Xe+ ions

A study of the radiational defects in nickel after implantation of Xe+ ions

Defect structure evolution from cascade damage in 14 Mev neutron irradiated nickel and nickel alloys

Abstract D-T neutron irradiation of nickel and 4 nickel based 2 at.% alloys were performed using RTNS-II at 300 to 700 K and fluences up to 1023 n/m2. The role of free point defects was detected by the comparison of defect structures produced by irradiation of material as thin foil and those irradiated as bulk. The analysis of vacancy clusters in thin foil nickel gives the average distance between sub-cascades to be 10 nm and 14 keV as sub-cascade energy. In bulk samples interstitial loops were formed; the major clustered vacancy defects in nickel at the lower temperatures were stacking fault tetrahedra, and voids at the higher temperatures. This difference reflects the variation of the stability of tetrahedra with temperature. Under-sized solutes (Si) and extremely over-sized solutes (Sn) enhanced the formation of loops in matrix, whereas moderately over-sized solutes (Cu,Ge) enhanced the formation of loops near dislocations. In the latter case, voids were observed since free point defects can diffuse long distances.

Relation between the strength characteristics of iron and nickel and the electronic structure of defects by positron annihilation spectroscopy

A relation between the parameters characterizing the fracture due to cyclic deformation and the electronic structure (ES) of defects in iron and nickel is discussed. The change of ES of defects in nickel is characterized both, by the change of the electron density and its redistribution between the conduction and ionic core states. In technical iron, the change of ES in defects is probably connected also with the decoration of the surface of defects by carbon atoms and/or with the possible micro-nuclei of a new phase initiated by the deformation process. [Russian Text Ignored].

Investigation of the state of helium and radiation defects in He-irradiated nickel and copper by glancing angle X-ray diffraction

Abstract Damage caused by low energy helium implantation in nickel and copper has been investigated for the first time by glancing angle X-ray diffraction technique. The damage confined only to the near surface region, typically few thousands A, comprises of displacement type damage and implanted species. As X-ray penetration depth (for 99% absorption) can be continuously varied as a function of angle of incidence and X-ray wavelength, accurate lattice parameter measurements (back-reflection) can be used to obtain cumulative information regarding long- and short-range strain field of defects. High purity nickel and copper foils were irradiated at room temperature with 100 keV helium ions to fluence levels ranging from 1016 to 1018 ions/cm2. The results show: (a) simultaneous presence of two defect complexes of opposite strain field character in both nickel and copper, (b) mobility of vacancies is an important parameter for determining the nature and the strength of defect complex, and (c) local strains du...

Calculations of the properties of single and multiple defects in nickel

The properties of single and multiple defects in Ni were calculated by molecular dynamics simulation using an effective interaction potential derived with the aid of a new method developed by Dagens for transition metals. The formation and migration energies of single vacancies are 1.33 and 0.90 eV, respectively. Di-, tri- and tetravacancies are weakly bound, with respective binding energies of 0.004, 0.10 and 0.24 eV. The divacancies are more mobile than the single vacancies, having a migration energy of 0.47 eV. Self-interstitials are found to be stable in the (100) dumbbell configuration; their energies of formation and migration are 4.16 and 0.12 eV, respectively. Multiple interstitials are strongly bound; like the single dumbbell interstitials, di-interstitials are highly mobile. The respective binding and migration energies for di- and tri-interstitials are 1.13 and 0.17 eV, and 2.67 and approximately 0.50 eV. The theoretical results are compared with the available experimental measurements and with previous defect calculations based on a short-range empirical potential.

Position annihilation investigations into the interaction between hydrogen atoms and defects in electron-irradiated nickel

The interaction between hydrogen and defects created by electron irradiation has been studied in nickel samples using the positron annihilation technique. No experimental evidence was found for the trapping of hydrogen atoms in defects. The observed increase in the probability of annihilation of positrons by low momentum electrons results most probably from the hydrogen-induced agglomeration of vacancies into voids. The possibility cannot be excluded, however, that the positrons are annihilated by electrons surrounding the protons, i.e. from the trap-like regions in which local concentrations of electrons are higher than average.

Magnetic hyperfine fields of vacancy-associated119Sn in ion-implanted nickel

Magnetic hyperfine fields of119Sn impurity defects in nickel have been investigated by Mossbauer emission spectroscopy. Radioactive119Xe isotopes were implanted, annealing was performed after119Xe had decayed to119Sb. At least five different components with well-defined magnetic hyperfine fields, isomer shifts and Debye temperatures are identified in the rather complex spectra. One of these (B=2T) is known to be due to substitutional Sn. The hyperfine fields of the other components are pronouncedly larger (B=9T, B=15T, and B=17T, respectively, for single crystals). These defects are proposed to be Sn-multivacancy defects.

Interaction of deuterium with lattice defects in nickel

The trapping of ion-implanted deuterium (D) in fee Ni is investigated by ion-beam-analysis techniques. Two lattice-defect traps have been observed with trap-binding enthalpies 0.24 eV and 0.43 eV referred to an untrapped solution site. The lattice location of D when associated with the defect traps is obtained by the channeling technique following anneals at various temperatures. The detailed analysis of these channeling data is based on a comparison with multirow continuum-model calculations of the angular yields for different D positions. These channeling calculations are extended by introducing a parameter δψ which encompasses the spreading in transverse energy caused by effects such as, for example, electron and nuclear multiple scattering. Also new and improved theoretical calculations based on the effective medium scheme of the equilibrium positions of H isotopes at defects, especially vacancies, are presented. The calculations show that D is delocalized over the entire vacancy, with a maximum density in the region between the vacancy and the nearest octahedral site. This picture is supported by the finding that the channeling data for D trapped to vacancies cannot be interpreted in terms of a single lattice site, and preference in site occupancy is found for D displaced from the vacancy towards the octahedral and (smaller) tetrahedral sites, respectively.

Helium decoration of impurities in metals

Equal numbers of He atoms and vacancies are liberated during the thermal annealing of helium-doped nickel samples at a temperature at which substitutional He atoms are released from the vacancies they occupy. We observed that the He atoms do not escape from the implanted region, but are retrapped in deeper traps. We have shown that He atoms can be quantitatively retrapped by In and Sb impurity atoms to form decorated defects, provided the He concentration exceeds a critical value of a few tenths of an atomic per cent. At lower concentrations bubble formation is probably the dominant retrapping mechanism. The decorated defects in nickel consist of several vacancies and He atoms, and are most likely occupied by 2 He atoms, arranged in a configuration with high symmetry such that the symmetry axis points along the 〈111〉 direction. This is the same as in copper, but different from aluminium where the orientation is along the 〈100〉 direction. Decorated defects are usually very stable against thermal annealing.

Defect trapping of ion-implanted deuterium in nickel

Trapping of ion-implanted deuterium by lattice defects in nickel has been studied by ion-beam-analysis techniques in the temperature range between 30 and 380 K. The deuterium-depth profiles were determined by measuring either the α particles or the protons from the 3He-excited nuclear reaction D(3He,α)p, and the deuterium lattice location was obtained by means of ion channeling. Linear-ramp annealing (1 K/min) following a 10-keV D+ implantation in nickel produced two annealing stages at 275 and 320 K, respectively. The release-vs-temperature data were analyzed by solving the diffusion equation with appropriate trapping terms, yielding 0.24 and 0.43 eV for the trap-binding enthalpies associated with the two stages, referred to as an untrapped solution site. The 0.24-eV trap corresponds to deuterium close to the octahedral interstitial site where it is believed to be trapped at a vacancy, whereas it is suggested that the defect correlated with the 0.43-eV trap is a multiple-vacancy defect. The previously air-exposed and electropolished nickel surface was essentially permeable; the surface-recombination coefficient was determined to be K≳10−19 cm4/s at 350 K.

Diffusion Mechanism of Nickel and Point Defects in Silicon

The in-diffusion of nickel into silicon and the annealing of nickel in silicon have been studied experimentally at 900°C. The variations in concentration of substitutional nickel with time are described well by an exponential function predicted from a dissociative mechanism, in both the in-diffusion and annealing processes. The time constant in the annealing process is substantially independent of the initial concentration of substitutional nickel. These results support the theory that nickel in silicon diffuses by a dissociative mechanism and that the dominant point defects in silicon are vacancies.

Growth of fatigue cracks from casting defects in nickel–aluminium bronze

The initiation and early growth of fatigue cracks from casting defects has been studied in a nickel-aluminium bronze, to provide a basis for the prediction of fatigue lives of marine propellers operating in a service environment of sea water. Observations have been made on the growth of fatigue cracks from surface shrinkage cavities produced in the casting process. It was found that the cracks irzltiated very easlly and, wnen short, showed anomalously high growth rates. Three regimes of behaviour have been identified: (1) very short cracks; these cracks showed extremely high growth rates, which are related to the effects of stress concentration and interaction with the microstructure; (2) slightly longer cracks; these cracks showed anomalqus growth behaviour similar to that reported by other workers; and (3) longer cracks, whose propagation behaviour was the same as that exhibited by long through-cracks in single-edge-notched bend specimens. These short-crack studies were supplemented by work on long cracks which investigated the entire Paris curve from threshold to fast fracture. Effects of environment (air and sodium chloride solution), frequency, and mean stress were investigated, and particular interest was taken in near-threshold behaviour. Fatigue lives of components in service can be estimated from propagation data by integrating the Paris curve with respect to the number of cycles. This integration procedure has been examined critically and its major sources of inaccurac yare discussed. From an understanding of the early growth behaviour of cracks and of the effect of service variables on the propagation threshold, it has been possible to use the integration method to estimate the fatigue lives of ships’ propellers made from cast nickel-aluminium bronze and to comment on the desirable frequency of NDT inspection.

Lattice defects in single-crystal nickel deformed at 4.2°K

The kinetics of defect formation in a single crystal of nickel have been investigated at 4.2°K using the parameters of deformation and resistance measurements. A size effect of dislocation pile-up has been observed in the easy slip stage and the multiplication coefficient for the process has been evaluated. A sudden slowing of defect formation is observed in the intermediate stage of work hardening.

A computer simulation of point defects and planar defects in nickel

AbstractThe properties of point defects and planar defects in nickel are investigated using computer simulation techniques. An empirical pair potential consisting of nine cubic splines is derived for nickel. This potential reproduces the experimental vacancy formation and migration energies, the intrinsic stacking fault energy, and the elastic constants. The displacement fields, formation energies, and formation volumes are calculated for the vacancy, the saddle‐point configuration associated with vacancy migration, and six interstitial configurations. In addition, results are presented for the intrinsic and extrinsic stacking faults and the twin boundary. The vacancy results are in agreement with previous calculations but the interstitial formation energies are significantly larger than those calculated previously. The crowdion is found to be the most stable interstitial configuration with a formation energy of 8.77 eV and formation volume of 0.42 atomic volumes. The energies of the twin, intrinsic, and extrinsic stacking faults are found to be 97, 158, and 199 mJm−2, respectively.

Symmetry of some lattice defects in nickel measured by DPAC

From DPAC measurements two defect-associated sites are known to exist after implantation of111In in nickel. Site A possesses high symmetry and does not show electric quadrupole interaction, while for site B a large axially symmetrical EFG is found. DPAC measurements on a Ni single crystal revealed that the symmetry axis of the EFG preferably points into a 〈111〉 direction. The defects are interpreted in terms of simple impurityvacancy clusters.

On the Formation of Secondary Defects in Nickel

On the Formation of Secondary Defects in Nickel

Voids in Quenched Nickel

The presence of three-dimensional voids in quenched metals has long been suspected, and voids have indeed been observed directly in a number of metals. These include aluminum, platinum, and copper, silver and gold. Attempts at the production of observable quenched-in defects in nickel have been generally unsuccessful, so the present work was initiated in order to establish the conditions under which such defects may be formed.Electron beam zone-melted polycrystalline nickel foils, 99.997% pure, were quenched from 1420°C in an evacuated chamber into a bath containing a silicone diffusion pump fluid . The pressure in the chamber at the quenching temperature was less than 10-5 Torr . With an oil quench such as this, the cooling rate is approximately 5,000°C/second above 400°C; below 400°C, the cooling curve has a long tail. Therefore, the quenched specimens are aged in place for several seconds at a temperature which continuously approaches the ambient temperature of the system.

The importance of defects in nickel on the catalytic dehydrogenation of formic acid at low pressures

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