High mechanical strength of Al-(V, Cr, Mn)-(Fe, Co, Ni) quasicrystalline alloys prepared by rapid solidification

Abstract

Nanogranular amorphous+fcc-Al phases were found to be formed in rapidly solidified Al94V4M2 (M=Fe or Co) and Al93V5Ni2 alloys. The grain size of the amorphous phase is 5 to 30 nm and of the fcc-Al phase 7 to 30 nm. Besides, the mixed structure consisting of nanoscale icosahedral (I) particles surrounded by an fcc-Al phase was formed in the rapidly solidified Al-V-M, Al-Cr-M and Al-Mn-M (M=Fe, Co or Ni) alloys examined in the present study. The particle size of the I-phase is about 15 to 70 nm and the interparticle spacing occupied by the fcc-Al phase is about 10 to 30 nm. The formation tendency of the nonequilibrium amorphous and I phases is greater for the V-containing alloy, followed by the Cr- and then the Mn-containing alloy. All these nonequilibrium phase alloys exhibit good bending ductility and the tensile fracture strength (σf) reaches about 1400 MPa for the amorphous+Al phases and about 1250 MPa for the I+Al phases. The σf values increase in the order of V>Cr>Mn and Fe>Co>Ni when the alloys with the same solute concentrations are compared. The high strength is attributed to the formation of the nanogranular amorphous+fcc-Al and I+fcc-Al phases. The high formation tendency of the amorphous phase for the V-containing alloy is presumably because the V element causes the formation of the stoichiometric I-phase with the lowest solute concentration and has the lowest diffusivity in the Al phase and more multiple peritectic reactions. The formation of the amorphous phase and the achievement of the high σf values for the Al-rich alloys without the lanthanide element are important as the basic information to devlop a new high specific strength material.