Formation of Quasicrystalline Alloy Powders by Mechanical Alloying

Abstract

Mechanical alloying (MA) was used to obtain quasicrystalline; phases Mg₃Zn_5-xAlx (x=2-4) and i-Mg₃₂Cu₈Al₄ starting from the elementary metal powders.Mechanical disordering(MD) of cubic Frank-Kasper (F-K) phases such as Mg₃₂(Zn, A1)₄₉ lead to formation of relative quasicrystalline structures as well.The X-ray diffraction patterns of i-phases are identical to those obtained by rapid quenching. SAD patterns of both MA and MD samples demonstrated 2, 3, 6, and 5-fold symmetry pictures.There are ten sets of Bragg spots with angles between them 36°. The values of the interplanar distances in i-Mg₃₂(Zn, Al)49 are d₁=0.141nm, d₂=0.228nm, d₃=0.369nm, d₄=0.597nm, d_n=d_n-1t, where t=(1+5^1/2)/2.The cubic phases Mg₃₂(Zn, Al)₄₉ and Mg32(Cu, Al)49 are F-K structures with local 5-fold symmetry units.The icosa-hedral structure can be described in terms of cubic F-K phase containing discli-nations.The MD of F-K phases lead to progressive broadering of X-ray peaks due to the structural, defects arising in cubic lattice and the icosahedral phases were formed apparently due to the formation of disclination network during MD.