Abstract
Small-angle X-ray scattering has been employed to study the stability of GP zones in two Al-Zn alloys during fatigue, in order to provide statistically sound information on this process. In a 5.3 at. pct Zn alloy containing l025 zones per m3 with an average diameter of 18 A, the normally sluggish coarsening was accelerated by fatigue at room temperature by factors of l06 to l07. No coarsening occurred for larger zones, except near a fatigue crack. Reverted samples aged rapidly during fatigue at room temperature, but in a reverted sample of Al-3.5 at. pct Zn cycled at 77 K no appreciable zone growth occurred. Upon warming this sample to room temperature (without any load) rapid clustering took place. These results imply that a vacancy fraction of 10-5 to l0-6 was produced by the fatigue, and this excess vacancy concentration appears to cause the growth during cycling at room temperature.
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