ULTRAHIGH STRENGTH OF RAPIDLY SOLIDIFIED AL96-XCR3CI1COX (X=1, 1.5 AND 2-PERCENT ALLOYS CONTAINING AN ICOSAHEDRAL PHASE AS A MAIN COMPONENT

An extremely high tensile strength (sigma(f)) of 1340 MPa combined wit h good bending ductility was obtained as a mixed structure consisting of nanoscale icosahedral (I) particles with a size of about 40 nm surr ounded by a thin fcc-Al layer with a thickness of about 2 nm in rapidl y solidified Al99-x-y-Cr(x)Ce1Co(y) alloys containing 0 to 5%Cr and 0 to 1.5%Co. Furthermore, each I-particle has a random orientation and c ontains a high density of phason defects and subnanoscale approximant crystalline regions. The replacement of Co by Mn, Fe, Ni or Cu causes the decrease in sigma(f) through the increases in the particle size of the I-phase and the width of the Al phase as well as the decrease in the density of phason defects in the I-phase. The unique mixed structu re is formed through the process of the precipitation of the primary I -phase, followed by the solidification of the remaining liquid as an A l phase. The good ductility for the alloys containing the I-phase as a main constitute is presumably due to the ease of the sliding along th e interface between I- and approximant crystalline phases as well as t he existence of the Al phase which surrounds the I-phase. The high sig ma(f) value is interpreted by the effective contribution of the I-part icles as a strengthening phase because of the achievement of a good du ctile nature for the mixed phase alloys.