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 with good bending ductility was obtained as a mixed structure consisting of nanoscale icosahedral (I) particles with a size of about 40 nm surrounded by a thin fcc-Al layer with a thickness of about 2 nm in rapidly 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 contains 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 structure is formed through the process of the precipitation of the primary I-phase, followed by the solidification of the remaining liquid as an Al 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 the interface between I- and approximant crystalline phases as well as the existence of the Al phase which surrounds the I-phase. The high sigma(f) value is interpreted by the effective contribution of the I-particles as a strengthening phase because of the achievement of a good ductile nature for the mixed phase alloys.