Analytical TEM of i-phase in an Al_(94)Mn_2Be_2Cu_2 alloy

摘要

Quasicrystals form an additional state of matter to those of crystalline and glassy. The atom positions are ordered but with non-crystallographic rotational symmetry and without three-dimensional periodicity [1]. The first icosahedral quasicrystal (i-phase) discovered in the Al-Mn system was metastable. It could be formed by rapid solidification, but not during conventional casting, e.g. by casting into metallic dies. Several ternary and quaternary alloys based on the Al-Mn system were developed during the last decade, forming quasicrystals during conventional casting. Yet, considerable amounts of crystalline intermetallic phases could not be avoided [2]. Recently, the Al_(94)Mn_2Be_2Cu_2 alloy has been developed exhibiting very high quasicrystalline forming ability. The i-phase formed at moderate cooling rates typical for the conventional die casting (around 1000 K/s) [3]. It is of great interest to study the i-phase in more detail and find out whether the increased quasicrystalline ability can be attributed to incorporating of Be and Cu in the i-phase. Analytical TEM was chosen as a convenient method due to small particle sizes, the specifics of the quasicrystalline structure and the content of beryllium in the alloy.