STP870

    Nonequilibrium Segregation and Phase Instability in Alloy Films During Elevated-Temperature Irradiation in a High-Voltage Electron Microscope

    Published: Jan 1985


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    Abstract

    The effects of defect-production rate gradients, caused by the radial nonuniformity in the electron flux distribution, on solute segregation and phase stability in alloy films undergoing high-voltage electron-microscope (HVEM) irradiation at high temperatures are assessed in this paper. Two-dimensional (axially symmetric) compositional redistributions were calculated, taking into account both axial and transverse radial defect fluxes. It was found that when highly focused beams were employed, radiation-induced segregation consisted of two stages: dominant axial segregation to the film surfaces at short irradiation times and competitive radial segregation at longer times. The average alloy composition within the irradiated region could differ greatly from that irradiated with a uniform beam, because of the additional atom transport from or to the region surrounding the irradiated zone under the influence of radial fluxes. As a result, damage-rate gradient effects must be taken into account when interpreting in situ HVEM observations of segregation-induced phase instabilities. The theoretical predictions are compared with experimental observations of the temporal and spatial dependence of segregation-induced precipitation in thin films of nickel-aluminum, nickel-germanium, and nickel-silicon solid solutions.

    Keywords:

    radiation-induced segregation, compositional redistribution, radiation-induced phase instability, radiation effects, point defects, thin films, high-voltage electron microscopy, computer modeling, radiation


    Author Information:

    Lam, NQ
    Scientists, Materials Science and Technology Division, Argonne National Laboratory, Argonne, IL

    Okamoto, PR
    Scientists, Materials Science and Technology Division, Argonne National Laboratory, Argonne, IL


    Paper ID: STP37378S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP37378S


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