Nanoscale twinning in Fe–Mn–Al–Ni martensite: a backscatter Kikuchi diffraction study

Abstract

Iron-based Fe–Mn–Al–Ni shape-memory alloys are of rather low materials cost and show remarkable pseudoelastic properties. To further understand the martensitic transformation giving rise to the pseudoelastic properties, different Fe–Mn–Al–Ni alloys have been heat treated at 1473 K and quenched in ice water. The martensite, which is formed from a body-centred cubic austenite, is commonly described as face-centered cubic (f.c.c.), even though there are also more complex, polytypical descriptions of martensite. The presently studied backscatter Kikuchi diffraction (BKD) patterns have been evaluated, showing a structure more complex than simple f.c.c. This structure can be described by nanoscale twins, diffracting simultaneously in the exciting volume. The twinned structure shows a tetragonal distortion, not uncommon for martensite in spite of the lack of interstitial elements. These features are evaluated by comparing the measured BKD patterns with dynamically simulated ones.

Crystallography of Fe–Mn–Al–Ni Shape Memory Alloys

“…2, the predicted orientation relationships closely correspond to a Pitsch OR [34] ideally expressed as 100 f g A1=fct jj 110 È É A2 and h011i A1=fct jjh111i A2 when it refers to the variants listed in Table 2. [16]. This revealed the tetragonality of the martensite, which was later confirmed by SAED [20] and attributed to a D0 22 superstructure likely inherited from D0 3 ordering in the austenite (see also ''Assessment of Existing Crystallographic Information'' section).…”

“…In order to perform a sufficiently good background subtraction, which tends to be challenging for coarse-grained materials, Fe 40 Ni 40 B 20 metallic glass was additionally embedded and polished during sample preparation. Due to the similar electron density, compared to the investigated material, the static EBSD background generated from the metallic glass can be used for a subsequent EBSD investigation [16]. For the purpose of identification of grain (and phase) boundary, grains were identified to consist of a minimum of 20 neighbored pixels, where separate grains were assigned in case of a misorientation of 10°.…”

“…For the purpose of identification of grain (and phase) boundary, grains were identified to consist of a minimum of 20 neighbored pixels, where separate grains were assigned in case of a misorientation of 10°. For more details on the EBSD analysis, see [16].…”

“…The investigations on the martensite's structure in Fe 43.5 Mn 34 Al 15 Ni 7.5 were supplemented by investigations on Mn-rich Fe-Mn-Al-Ni alloys [16]. EBSD analysis revealed a finely twinned tetragonal martensite, whereas SAED patterns revealed the presence of a tetragonal (twinned) D0 22 fcc superstructure, which is related via the Bain strain to a D0 3 (or Heusler) bcc superstructure.…”

Nucleobindin-2 consists of two structural components: The Zn2+-sensitive N-terminal half, consisting of nesfatin-1 and -2, and the Ca2+-sensitive C-terminal half, consisting of nesfatin-3

“…For each sample, 10 independent frames (exposure time 600 s per frame) were recorded using a PILATUS3 1 M detector (DECTRIS Ltd., Baden-Daettwil, Switzerland). Scattering data for ggNucb2 and hsNucb2 were integrated using Foxtrot [114] and processed using the SAS data analysis module from the ATSAS package [115] .…”