A HREM study of the interfacial structure of γ' precipitate plates in an Al-15 wt % Ag alloy

Abstract

The interfacial structure and growth kinetics of γ' and γ (Ag2Al) precipitate plates in Al-Ag alloys have been extensively studied by conventional TEM methods. Although most results have confirmed the predictions of the general theory of precipitate morphology proposed by Aaronson, some new questions have arisen. The present study is an attempt to address the specific points of contention concerning the details of ledge growth in this system.An Al-15 wt % Ag alloy was solution treated at 500°C for 30 minutes, quenched and aged for 30 minutes at 350°C. Thin foils were jet polished in a nitric acid-methanol solution and lightly ion-beam milled prior to insertion into a JE0L 200 CX microscope. A through focus series of [110] axial lattice images was taken at 200,keV, using a pointed LaB6 filament and an objective aperture of radius 0.64Å-1.Fig. 1(a) shows twoend-on γ' plates about 200Å thick and lying on {111} planes as evident from the diffraction pattern in Fig. 1(b).