Structure and morphology of S-phase precipitates in aluminum
This work presents a crystallographic and morphological analysis of S-phase precipitation in Al alloys. Using quantitative high resolution electron microscopy, four models for the crystal structure of the S-phase (Al{sub 2}CuMg) in Al-based alloys are critically evaluated, and a new model is proposed. This model is identical to that of Perlitz and Westgren, but with an exchange of Cu and Mg. Two distinct precipitate morphologies are observed. Both are laths elongated along {l{underscore}angle}100{r{underscore}angle} directions common to the matrix and the precipitate and lie on {l{underscore}brace}021{r{underscore}brace} planes of the matrix. Type 1 precipitates have interfaces of the type (021){sub Al}{parallel}(001){sub S} while type 2 precipitates have interfaces of the type (021){sub Al}{parallel}(0.43){sub S}, i.e., the two types differ in the S-phase lattice plane that is conjugate to the {l{underscore}brace}021{r{underscore}brace}{sub Al} habit plane. The interface plane of type 1 precipitates tends to be atomically flat containing only growth ledges while that of type 2 precipitates is stepped. The orientation relationship of the two types of precipitate differs by a rotation of about 5{degree} around the lath axis. The difference between the two types of precipitate is discussed in terms of their lattice correspondence, and type 2 precipitates are shown to follow an invariant line strain. Moire analysis of lattice distortions revealed that {l{underscore}brace}020{r{underscore}brace}{sub Al} planes remain undistorted while {l{underscore}brace}002{r{underscore}brace}{sub Al} planes suffer significant shear during S-phase nucleation.
- Research Organization:
- Lawrence Berkeley Lab., CA (US); Univ. of Belgrade (YU)
- Sponsoring Organization:
- US Department of Energy
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 20005375
- Journal Information:
- Acta Materialia, Journal Name: Acta Materialia Journal Issue: 15-16 Vol. 47; ISSN 1359-6454; ISSN ACMAFD
- Country of Publication:
- United States
- Language:
- English
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