Precipitation Under Cyclic Strain in Solution-Treated Al-4wt%Cu II: Precipitation Behavior
LOS ALAMOS NATIONAL LAB NM MATERIALS SCIENCE AND TECHNOLOGY DIV
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Solution-treated Al-4wtCu was strain-cycled at ambient temperature and above, and the precipitation behavior investigated by Transmission Electron Microscopy TEM. In the temperature range 100 degrees C to 200 degrees C, precipitation of theta-prime-prime appears to have been suppressed, and precipitation of theta-prime promoted. Anomalously rapid growth of precipitates appears to have been facilitated by a vacancy super-saturation generated by cyclic strain, with a diminishing effect observed at higher temperatures due to the recovery of non-equilibrium vacancy concentrations. The theta-prime precipitates generated under cyclic strain are considerably smaller and more finely dispersed than those typically produced via quench-aging due to their heterogeneous nucleation on dislocations, and possess a low aspect ratio and rounded edges of the broad faces due to the introduction of ledges into the growing precipitates by dislocation cutting. Frequency effects indicate that dislocation motion, rather than extremely small precipitate size, is responsible for the reduction in aspect ratio.
- Properties of Metals and Alloys
- Fabrication Metallurgy