Preparation and mechanical properties of highly densified nanocrystalline Al

The preparation of highly densified nanocrystalline (NC) Al was conducted i n three steps. First, the NC Al powder was synthesized by an active H-2 pla sma evaporation method. Then, the NC Al powder was compacted at room temper ature into disk-shaped samples with a 25-mm diameter and 2-mm thickness and was sintered at 620 degrees C or 635 degrees C (sintered NC Al), The sinte ring does not result in grain growth. Finally the sintered NC Al was rolled at room temperature into sheet samples with a 1-mm thickness and 99 pet re lative density (cold-deformed NC Al). The microhardnesses and tensile prope rties of the sintered NC Al and cold-deformed NC Al were tested at room tem perature. The results show that their strengths are basically the same, and the yield strengths (sigma(0.2)) and tensile strengths (sigma(b)) are 12 t o 16 and 5 to 6 times those of annealed coarse-grained Al, respectively, bu t the elongation to failure of the cold-deformed NC Al is up to 8 pct, whic h is 2 times that of the sintered NC Al and higher than that of cold-deform ed, coarse-grained Al by 30 pct. The failure features of the sintered NC Al and cold-deformed NC Al belong to typical plastic fracture with ductile di mples, and the mechanism of failure is transgranular shear fracture.