High Resolution Lattice Images of G.P.Zones and Solute Clusters in Al-Cu and Cu-Be Alloys
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HIGH RESOLUTION LATTICE IMAGES OF G.P.ZONES AND SOLUTE CLUSTERS IN Al-Cu AND Cu-Be ALLOYS
H. Yoshida*, H. Hashimoto**, Y. Yokota** and M. Takeda** *Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-04; of Applied Physics, Osaka University, Suita, Osaka 565, Japan
"**Department ABSTRACT
Atomic structures of G.P. zones and solute clusters in Al-Cu and Cu-Be alloys are studied by the atom The images of resolution electron microscope images. plate-like G.P. zones appear as dotted images with various brightnesses along (200) lattice planes. The solute clusters are also observed along (111) lattice planes.
INTRODUCTION The plate-like G.P. zones formed on (100) planes in Al-Cu and Cu-Be alloys have been observed in the conventional bright-field images (BFI) as line-shape contrasts due to their strain fields and as sharp bright line pairs in the weak-beam images (WBI), when they are viewed edge-on [1-5]. The lattice imaging methods have been applied to observation of G.P. zones in Al-Cu alloys and fine informations on the atomic arrangement around G.P. Recently the structure consisting of a few zones have been studied(6-12]. layers of solute Cu atoms was reported for G.P.(I) zones in Al-Cu alloys based on the results of X-ray diffuse scattering[13) and field ion microscopy[15-, reactivating the discussion on the structures of G.P. Based on the atom resolution electron microscope images zones[9-15,19j. taken by the multi-beam imaging method under the axial and tilted beam aberration free focus (AFF) condition[16,17], the atomic structures of solute clusters and G.P. zones will be discussed in the present paper.
EXPERIMENTAL Disc specimens of 3 mm diameter cut from a sheet of 0.2 mm thick of an A1-3.97wt%Cu alloy were solution-treated at 530 C and then quenched into a 4 Sheets of 0.1 mm thick of Cu-0.99 and-l.87wt%Be alloys water at 0 C[ j. were solution-treated at 780 C in a hydrogen atmosphere and then waterquenchedL20j. The quenched specimens were aged in an oil bath at various temperatures. The aged specimens were initially thinned by a jet of 15% HNO3-water solution at room temperature and then finally electropolished in a 35% HNO3-ethanol solution at below -30 C[4,5]. Observations were carried out using the high resolution electron microscope JEM-120C with a LaB 6 gun and a THG1 goniometer, operated at 100 kV[16,17]. The images were photographed under the axial and tilted The incident beam which was parallel to the beam AFF conditions[17,191. direction of or of the specimen crystal was tilted, so that the centre of 200, 020, 220 and 000 reflections or 111, 111, 022 and 000 reflections, respectively, was on the optical axis and the images were The atom resolution images were interpreted in photographed.l7,19i. comparison with the computed images calculated by the multi-slice method zonestl9j. using the previous and the modified models of G.P.(I) and (II)
Mat.
Res. Soc.
Symp. Proc. Vol.
21 (1984) Published by Elsevier Science Publishing Co.,
Inc.
132
RESULTS AND DISCUSSIONS When the incident
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