The effect of a dc on the interdiffusivity D in the Cu-Ni system was investigated over the temperature range of 650-850 degrees C and at current densities in the range of 0-1000 A cm(-2). Interdiffusivities were calculated using the Sauer-Freise-den Broeder method and the values calculated in the absence of a current were in agreement with previously published results. The influence of the current on D depended on its direction relative to the two interfaces in the trilayered Cu-Ni-Cu samples. When the electronic flow was from Ni to Cu (cocurrent interface), the interdiffusivity showed a marked increase relative to copper content but was unchanged when the electronic flow was from Cu to Ni (countercurrent interface). The increase of D in the cocurrent interface depended on concentration and temperature. At lower temperatures, the increase becomes significant at higher copper concentrations but for the same value of current density, the increase is apparent at lower concentrations. The effective activation energy of interdiffusivity depended on concentration and decreased with the application of a current. The decrease was largest for higher copper concentrations. The results are interpreted in terms of a proposed vacancy-atom interaction for copper with the implication that the electron wind effect on Cu is counteracted by the effect of vacancies. (c) 2007 American Institute of Physics.

The effect of a pulsed dc on the sintering of copper spheres to copper plates was investigated. It was shown that the current had a marked effect on neck growth between the spheres and the plates. The enhancement of sintering under the effect of the current was attributed to electromigration. Microstructural observations on fracture surfaces of necks formed under high currents showed considerable void formation. It was also observed that the current resulted in increased evaporation and the formation of bunched evaporation steps. Formation of these steps and their location relative to the neck were consistent with current density distributions. The results of this investigation provide direct evidence for the role of the current in the sintering in the pulse electric current sintering method. (c) 2007 American Institute of Physics.

The effect of a dc current on the crystallization of Vit1A (Zr42.6Ti12.4Cu11.25Ni10Be23.75) and PCNP (Pd40Cu30Ni10P20) metallic glasses was investigated. Samples were isothermally annealed with and without the current, at 623 and 577 K for the two glasses, respectively. Small-angle neutron scattering analyses showed that in the absence of a current, the annealed Vit1A samples were amorphous, but the imposition of a current enhanced the crystallization process, increasing both the size and volume fraction of the crystallites. Similar general observations were seen for the PCNP glass. Differential scanning calorimetry patterns of Vit1A samples indicate a lower thermal stability of samples annealed with a current. (C) 2004 American Institute of Physics.

Solid solutions of TiB2-WB2 were densified and annealed simultaneously to cause the decomposition into the phases (Ti,W)B-2 and (W,Ti)B-2. Ni and Co were added to solid solutions formed by induction field activated combustion synthesis. The presence of these metals as additives markedly enhanced the kinetics of the subsequent decomposition process. With these additives, decomposition to the two phases occurred within minutes (360 s) in contrast to hours when the solutions did not include the additives. The phases resulting from decomposition, (Ti,W)B-2 and (W,Ti)B-2, were identified by X-ray to have the hexagonal AIB, and W2B5 structures, respectively. The precipitated phase, (W,Ti)B-2, occurred as elongated grains with aspect ratios of as high as about 10 in samples containing Ni as the additive.

The effect of the application of a dc current on the annealing of point defects in Ni3Ti was investigated by positron annihilation spectroscopy. An increased defect annealing rate was observed under the influence of the current and was attributed to a 24% decrease in the activation energy of mobility. The results are interpreted in terms of the electron wind effect and the complex nature of diffusion in ordered intermetallic phases. They provide direct evidence for an increase in defect mobility in ordered intermetallics under the influence of a current. (C) 2004 American Institute of Physics.

Fully stabilized nanometric zirconia samples with varying degrees of porosity and grain sizes were analyzed using the coincidence Doppler broadening mode of the positron annihilation spectroscopy (PAS). A decrease in the low-momentum fraction was observed and coincided with a decrease in porosity. In addition to pores, it is proposed that defects in the negatively charged grain-boundary space region act as positron trapping centers; their effectiveness decreases with an increase in grain size. It is shown that PAS is sensitive to small grain-size differences within the nanometric regime in these oxide materials. (c) 2006 American Institute of Physics.

Boron carbide (B4C) was synthesized from the elements at temperatures ranging from 1300 degrees to 2100 degrees C using the spark plasma synthesis method. Significant densification commenced at about 1500 degrees C and was accompanied by a corresponding decrease in the defect structure of this carbide. Changes in the X-ray diffraction patterns were in agreement with predictions of simulation studies based on the presence of twins. Transmission electron microscopy observations were consistent with the experimental observations and the modeling predictions.