J.F. Nie

Effects of precipitate shape and orientation on dispersion strengthening in magnesium alloys

Abstract This paper reports results on the development of the Orowan equation appropriate for magnesium alloys strengthened by rationally-oriented, shear-resistant precipitate plates/rods. Comparisons of identical volume fractions and number densities of precipitates per unit volume indicate that plate-shaped precipitates that form on prismatic planes of the magnesium matrix phase are most effective for dispersion strengthening.

Atom probe characterization of plate-like precipitates in a Mg–RE–Zn–Zr casting alloy

Abstract This paper demonstrates that the three-dimensional atom probe (3DAP) is capable of characterizing nanoscale precipitates in magnesium alloys. Combined application of 3DAP and transmission electron microscopy reveals that the major precipitate phase in a Mg–2.4wt.%RE–0.4wt.%Zn–0.6wt.%Zr alloy has an ordered G.P. zone structure and a composition of approximately 3.2 at.% Nd, 1.0 at.% Ce and 1.2 at.% Zn.

Atomic structure of high-index α2:γm boundaries in a Ti–46.54 at.%Al alloy

Abstract Planar, high-index interphase boundaries developed during the α → γ m transformation in a Ti–46.54% Al alloy were re-examined with a 3-D near-coincidence site analysis. Pairs of low-index planes, fulfilling the Zhang and Purdy [Philos. Magn. A 68 (1993) 279] minimum mismatch criterion, meet along their edges. Atoms at these edges commingle almost linearly, thereby producing a kinetic barrier to boundary migration.

Transmission electron microscopy of Zr-Zn precipitate rods in magnesium alloys containing Zr and Zn

Rod-shaped Zr–Zn particles are commonly observed within individual α-Mg grains in magnesium alloys containing both Zr and Zn elements. In the present study, the identity, morphology, and orientation of such solid-state precipitate particles formed in a Mg–1Ca–1Zn–1Zr (wt.%) alloy have been characterized using analytical transmission electron microscopy and electron microdiffraction. It is found that these particles have a tetragonal crystal structure similar to that of Zn2Zr3 (P42/mnm, a = 0.768 nm, c = 0.699 nm). Three distinguishably different orientation relationships are observed between the Zn2Zr3 and matrix phases. But the long axes of the rods are invariably parallel to the [001] direction of the Zn2Zr3 phase.

Aspects of the surface relief definition of bainite

Abstract Criticisms of reports that ferrite laths have a sessile interfacial structure are refuted. A local lattice correspondence, achieved across coherent regions between interfacial defects, suffices to produce surface reliefs and martensitic crystallography [Prog. Mater. Sci. 42 (1997) 101]. However, formation of tent-shaped surface reliefs by monocrystalline laths/plates is inconsistent with martensitic growth.