Xuefei Huang

Transmission electron microscopy investigation and interpretation of the morphology and interfacial structure of the ɛ′‐Mg54Ag17 precipitates in an Mg–Sn–Mn–Ag–Zn alloy

The morphology and interfacial structure of the ∊′-Mg54Ag17 precipitates in a peak-aged Mg–Sn–Mn–Ag–Zn alloy have been investigated using transmission electron microscopy. A typical ∊′-Mg54Ag17 precipitate exhibits a (0001)α habit plane and three pairs of side facets, with two major pairs of facets being in irrational orientations. The orientation of each preferred interface is normal to a vector connecting two adjacent diffraction spots from different phases (Δg). Using the constrained coincidence site lattice (CCSL) model, the interface orientations have been interpreted according to the degree of matching on the interfaces. The detailed stepped structures in the irrational facets and dislocation configurations in the side facets have been predicted using the secondary CCSL (II-CCSL) and the secondary O-lattice model. Both the calculated terrace/ledge and dislocation configurations in side facets are in good agreement with the high-resolution transmission microscopy observations.

Long-period stacking ordered structures in Mg–3Cu–1Mn–2Zn–1Y damping alloy

Abstract 14H, 18R and 24R long-period stacking ordered (LPSO) structures were observed in the as-cast Mg–3Cu–1Mn–2Zn–1Y damping alloy using transmission electron microscopy (TEM). These LPSO structures contained Mg, Y, Cu and Zn and thus they were quaternary phases. Sharp diffraction pattern of the 24R structure was obtained and the angle between g 1 00α and g 100 24R was measured to be 5.03°. During high resolution TEM observations, lattice fringes with two characteristic spacings were observed within the 24R structure. Based on the experimental results, 6H, 7H and three 8H are suggested as the building blocks of 18R, 14H and 24R structures, respectively. The 24R unit cell can be interpreted as the stacking of 8H building blocks in the same shear direction with a shear angle of about 5.03°. The imperfect 24R structures are in order or disorder arrangements of principal 8H and minor 6H blocks. This double-block structure model is also applicable to other reported defects in LPSO structures.