1ST ATTEMPT TOWARDS THE DIRECT DETERMINATION OF THE GUINIER-PRESTON ZONES (GP1) COPPER CONTENT IN AL-1.7 AT PERCENT CU ALLOY

Starting from recent results on the observation of atomic monolayers Guinier-Preston zones (GP1) in Al-1.7 at%Cu alloy, by means of atomic resolution in transmission electron microscopy, the authors try to detect directly the concentration of Cu in GP1 zones. Preliminary results, obtained with transmission electron microscopes equipped with a field emission gun (FEG), are presented. They give a content of copper of the order of 50% or less. The problem of damaging the crystalline ordering of the zones under the beam is discussed. Above the displacement threshold, direct knock-on of electrons with aluminium nucleus is the major damaging interaction. This effect is more important for the direct determination of the copper concentration in the zones by means of EELS or X-ray elemental analysis. It is concluded that sub-threshold electron microscopy has to be preferably used.