Compositional analysis of the icosahedral phase in rapidly quenched Al-Mn and Al-V alloys

The formation ranges and alloy compositions of icosahedral phases in rapidly quenched Al-Mn and Al-V alloys containing 12.5 to 25 at. pct Mn and V, respectively, were examined by X-ray diffractometry and analytical transmission electron microscopy. The icosahedral phase was found to appear in a wide range of compositions below about 23 at. pct Mn and below about 18 at. pct V, but the formation of the icosahedral single phase was limited only in the vicinity of about 22.5 at. pct Mn. The analytical solute concentration in the icosahedral phase is not always constant and increases continuously from about 17 to 23 at. pct Mn and about 18 to 21 at. pct V with increasing nominal solute concentration. Thus, the icosahedral phase in rapidly quenched Al-Mn and Al-V alloys can be approximately formulated to be Al₄Mn and A1₄V with a maximum deviation of about 3 at. pct Mn or 2 at. pct V from the stoichiometric ratio.     

Formation of microstructure of the icosahedral phase in rapidly solidified aluminium-chromium alloys

Rapid solidification of AlCr alloys resulted in the nucleation and growth of the icosahedral phase in the 14–36 wt% Cr range. The highest volume fraction of this phase was obtained between 21–26 wt% Cr. It was found that the different alloy compositions contain a variety of morphologies and microstructures which also depend on location regarding the cross section of the ribbon. The icosahedral phase is not stoichiometric and its maximum Cr content is between 26–30 wt% Cr. In the higher alloy compositions the stable intermetallic ϵ phase grows epitaxial on the icosahedral phase with a distinctive orientation relationship.     

Investigation on the icosahedral quasicrystal phase in Mg70.8Zn28Nd1.2 alloy

Mg70.8Zn28Nd1.2 (mole fraction) alloy containing icosahedral quasicrystal phase (I-phase) was prepared under conventional metal casting conditions. The microstructure, phase constitution and phase structure of the alloy were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and transmission electron microscopy (TEM). The re-sults showed that the spherical phase in MgT70.8Zn28Nd1.2 alloy was a simple icosahedral quasicrystal with stoichiometric composition of Mg40Zn55Nd5 and quasi-lattice of 0.525 nm. In this research, the as-cast microstructure of Mg70.8Zn28Nd1.2 alloy mainly consisted of Mg40Zn55Nd5 icosahedral quasicrystal phase and Mg7Zn3 columnar crystal matrix. In the growing process of Mg40Zn55Nd5 icosahedral qua-sicrystal phase, the growth morphology mainly depended on interface energy, adsorption effect of Nd and cooling rate.