High-resolution electron microscopy observations of the interface structure of continuous precipitates in a Mg-Al alloy and interpretation with the O-lattice theory

Abstract

High-resolution electron microscopy observations of the interface structure of continuous precipitates in a Mg-Al alloy and interpretation with the O-lattice theory, Philosophical Magazine A, 71:1, 187-204,

Interpretation of precipitation crystallography of Mg17Al12 in a Mg-Al alloy in terms of singular interfacial structure

“…[2] The morphology of these precipitates, both continuous and discontinuous, has been reported in a number of studies. [3,6,7] It is widely accepted that most of the continuous precipitates, which have a better strengthening effect, appear as large platelets with two main interfaces (the habit plane and the major side facet). [7] The orientation relationship (OR) between the continuous precipitates (␤, bcc) and the matrix (␣, hcp) is usually described by the Burgers OR, i.e., (0 1 1) ␤ // (0 0 0 1) ␣ , [1 Ϫ1 1] ␤ // [2 Ϫ1 Ϫ1 0] ␣ , and the habit plane is (0 1 1) ␤ / (0 0 0 1) ␣ .…”

“…[14,15,16] The OR was interpreted based on the condition of the ⌬g vector's parallelism, for which a deviation of around 0.5 deg from the Burgers OR is required. [7] Duly et al [7] also determined the dislocations in the habit plane using the constrained coincidence site lattice/constrained complete pattern shift lattice (CSL/DSCL)* model and the O-lattice model, the *The CSL is often used to represent a secondary preferred state from which a misfit strain is considered to hold in an interface of large lattice misfit. [17,18] When a CSL is formed by interpenetration of lattice 1 and 2, all relative translations, between any pair of points in lattices 1 and 2, respectively, form a DSCL.…”

“…[7] The orientation relationship (OR) between the continuous precipitates (␤, bcc) and the matrix (␣, hcp) is usually described by the Burgers OR, i.e., (0 1 1) ␤ // (0 0 0 1) ␣ , [1 Ϫ1 1] ␤ // [2 Ϫ1 Ϫ1 0] ␣ , and the habit plane is (0 1 1) ␤ / (0 0 0 1) ␣ . [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Duly et al [7] first noticed a slight deviation between the directions of [1 Ϫ1 1] ␤ and [2 Ϫ1 Ϫ1 0] ␣ in a Mg-10 at. pct Al, indicating that the OR is not an exact Burgers OR.…”

Precipitation and Hardening in Magnesium Alloys

“…[27] Subsequent transmission electron microscopy studies [28,29] indicate that the orientation relationship is actually near the Burgers. The b precipitates in this orientation relationship have a plate morphology, with their broad surface parallel to (0001) a (Figures 1(b) and (c)).…”

“…[28,29,31] Despite the irrational orientation of these side facets with respect to both precipitate and matrix lattices, the major and minor side facets (Figure 2 respectively. Figure 2(a) shows the major side facet of a thin b plate that is embedded in the matrix phase.…”