Faceted interfaces: a key feature to quantitative understanding of transformation morphology

Abstract

Faceted interfaces are a typical key feature of the morphology of many microstructures generated from solid-state phase transformations. Interpretation, prediction and simulation of this faceted morphology remain a challenge, especially for systems where irrational orientation relationships (ORs) between two phases and irrational interface orientations (IOs) are preferred. In terms of structural singularities, this work suggests an integrated framework, which possibly encompasses all candidates of faceted interfaces. The structural singularities are identified from a matching pattern, a dislocation structure and/or a ledge structure. The resultant singular interfaces have discrete IOs, described with low-index g's (rational orientations) and/or Δg's (either rational or irrational orientations). Various existing models are grouped according to their determined results regarding the OR and IO, and the links between the models are clarified in the integrated framework. Elimination of defect types as far as possible in a dominant singular interface often exerts a central restriction on the OR. An irrational IO is usually due to the elimination of dislocations in one direction, i.e., an O-line interface. Analytical methods using both three-dimensional and two-dimensional models for quantitative determinations of O-line interfaces are reviewed, and a detailed example showing the calculation for an irrational interface is given. The association between structural singularities and local energy minima is verified by atomistic calculations of interfacial energies in fcc/bcc alloys where it is found that the calculated equilibrium cross-sections are in a good agreement with observations from selected alloys.

Atomic structures and migration mechanisms of interphase boundaries during body- to face-centered cubic phase transformations

“…To further determine IPB structures, we employed two crystallographic analysis approaches: near-coincidence site (NCS) calculation (Liang & Reynolds, 1998) and Ág vector analysis (Zhang & Weatherly, 2005;Zhang et al, 2016;Gautam & Howe, 2011). The NCS calculation was performed according to the procedure outlined by Liang & Reynolds (1998).…”

“…A consensus from geometrical models, such as the O-lattice model (Zhang & Yang, 2011), the invariant line model (Weatherly & Zhang, 1994) and the near-coincidence site model (Liang & Reynolds, 1998), is that the faceted IPBs in b.c.c.-f.c.c. systems are semi-coherent with a group of IPB dislocations located along the direction of the invariant line (Zhang et al, 2016). Two kinds of IPB dislocations with Burgers vectors of h110i fcc =2kh100i bcc and h110i fcc =2k h111i bcc =2 have been predicted by these geometrical models (Zhang & Weatherly, 2005).…”

A general and robust analytical method for interface normal determination in TEM

“…They can be considered as straight lines or flat planes. Accurately determining their crystallographic orientations is fundamental to unravel the mechanism of associated microstructure evolution [3]. In this context, the problem is restricted to the line direction or the interface plane normal determination, using a technique called trace analysis [4] [9].…”

Near Atomic Row Matching in the Interface Analyzed in Both Direct and Reciprocal Space

“…The crystallographic relationships include reproducible orientation relationships (ORs) between new phase and matrix, specific interfacial orientations (IOs), and so on [2,3]. To lower the interfacial energy, a special interfacial structure will form therein, thus the interfacial structure is the key to understanding the formation mechanism of these crystallographic features [4,5].…”