Dresden 2006 – scientific programme
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MM: Metall- und Materialphysik
MM 43: Diffusion III
MM 43.2: Talk
Friday, March 31, 2006, 12:45–13:00, IFW B
The effect of low stresses on creep and surface profiles of thin copper wires — •Vivek Srivastava1, Howard Jones2, and Geoffery Greenwood2 — 1Otto-von-Guericke-University Magdeburg, Institute of Materials Engineering & Testing, PO Box 4120, D-39016 Magdeburg, Germany — 2Department of Engineering Materials, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK
At low stresses and high temperatures, materials creep by stress directed diffusion of vacancies, i.e. diffusional creep. The creep rates and surface profile changes of wires, of diameters from 25*500 microns of high purity (99.995%) copper, have been investigated close to their melting temperature under stresses up to 0.4 MPa. Strain rate always varied linearly with stress. For the thinnest wires the rate was about twice the rate expected from Nabarro*Herring creep and more than one order of magnitude larger than expected from Harper*Dorn creep. For 500 microns wires, the measured rate was initially close to Harper*Dorn prediction but became constant only after longer durations at a level five times lower than this. The wire profiles near the closely perpendicular boundaries showed a smooth diameter increase or decrease depending on whether the stress was sufficient or insufficient to overcome the effect of the surface tension forces tending to shrink the wire. These profile changes indicated the location of vacancy sources and sinks and the measured steady state creep rates could be accounted for by the direction and magnitude of the vacancy fluxes.