THE INFLUENCE OF GRAIN-SIZE ON THE MECHANICAL-PROPERTIES OF NANOCRYSTALLINE ALUMINUM

Uniaxial tensile tests were performed at room temperature on nanocryst alline aluminium (n-Al) prepared by mechanical attrition and cold cons olidation with average grain size in the 20-40 nm range. The stress-st rain curves analysis shows an enhanced tensile strength and a reduced ductility of n-Al with respect to the coarse-grained material. Anyway, the strength increase is much lower than predicted by extrapolation o f the Hall-Petch relation to nanometer sized grains. Moreover, the str engthening rate (Hall Petch coefficient) is strongly reduced in compar ison with coarse-grained Al. The observed behaviour is discussed in co nnection with microstructure evolution during mechanical attrition. (C ) 1997 Acta Metallurgica Inc.