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Germanium network connecting precipitates in an Mg-rich Al-Mg-Ge alloy

Sammendrag

Precipitates in an Al–0.87Mg–0.43Ge (at.%) alloy, heat-treated for 16 h at 200°C, were investigated by transmission electron microscopy and annular dark-field scanning transmission electron microscopy (ADF-STEM). Earlier studies of Al–Mg–Si–(Cu) have shown that an Si network exists within all precipitates. Here, it was investigated whether the heavier, more easily detectable germanium atom would behave similarly. The precipitates were more similar to those found in Al–Mg–Si–Cu alloys with a high fraction of disordered phases than to ternary Al–Mg–Si. All precipitate cross-sections along [001]Al imaged by ADF-STEM showed that Ge atoms arrange in triangular columns separated by ∼0.4 nm. Along these columns, the precipitate’s 0.405-nm periodicity and coherency (along its needle axis) imply a Ge plane periodicity of 0.405 nm. A germanium network, therefore, exists in all precipitates in this alloy, with a hexagonal sub-cell (SC) a = b ∼ 0.4 nm, c = 0.405 nm, which is very similar to the Si network in Al–Mg–Si–(Cu). The network always appears as ordered. Disorder in a precipitate must, therefore, be caused by the other atoms in the structure between Ge atoms. One difference between precipitates of the ternary systems Al–Mg–Ge and Al–Mg–Si is the orientation of the diamond element network (SC) base in {001}Al. In Al–Mg–Ge, a <100>SC edge falls along <100>Al. This coincides with the orientation in some precipitates in quaternary Al–Mg–Si–Cu. In ternary Al–Mg–Si, one SC base is parallel with a <510>Al direction.

Kategori

Vitenskapelig artikkel

Språk

Engelsk

Institusjon(er)

  • Norges teknisk-naturvitenskapelige universitet
  • SINTEF AS

År

2010

Publisert i

Journal of Electron Microscopy

ISSN

0022-0744

Årgang

59

Hefte nr.

S1

Side(r)

S129 - S133

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