β-Al_4.5FeSi: A Combined Synchrotron Powder Diffraction, Electron Diffraction, High-Resolution Electron Microscopy and Single-Crystal X-ray Diffraction Study of a Faulted Structure

Abstract

A previous single-crystal X-ray and electron diffraction structure study [Rùmming et al. (1994). Acta Cryst. B50, 307±312] of the heavily faulted alloy phase -Al 4.5 FeSi has been extended by synchrotron powder data and further electron microscopy and diffraction observations. Re¯ections that were omitted in the single-crystal work could be included in the powder re®nement, which resulted in some adjustment of cell parameters and atom coordinates. The double c axis reported by some authors is explained by periodic faults in the structure, which is described in terms of a tetragonal sub-unit. Apparent discrepancies between re®nement from single-crystal and powder data are discussed brie¯y.

Electron microscope studies of Al-Fe-Si intermetallics in an Al-11 Pct Si alloy

“…EBSD patterns ( e.g., Figure 7(b)) of several particles such as shown in Figure 7w ere clearly indexed as the phase identified by Rømming et al as monoclinic b -Al 9 Fe 2 Si 2 . [23] Figure 7(c) showst he bright-field image of one of thesep articles and Figure 7(d) shows as elected area diffraction pattern indexed as [110], appearingn earlyi dentical to Figure 2(d) in Rømming et al [23] and Figure 3(e) in Hansen et al [24] As tandardless EDS analysis of the particles in TEM allows only as emiquantitative comparison of the two phases. As ummary of data taken from three different particles indexed as d phase and four particlesi ndexed as b phase is provided in Table II.…”

“…[5,10,13,19] However,t he most recent investigations [4,[20][21][22][23][24] havereached conflicting conclusionsregarding the structure and stability of these b -phase precipitates. Carpenter and Le Page describe [21] b -Al 5 Fe 2 Si as B-face centered orthorhombicw ith a 5 0.6184 nm, b 5 0.6250 nm, c 5 2.069 nm.…”

“…[3,5] Less subjective techniques, such as X-ray diffraction or convergent beam electron diffraction, have also been used to further understand the crystallography of thesep hases. [5,6,14,[20][21][22][23][24]26,[36][37][38][39][40][41] As mentioned, there haveb een some conflicting reports of crystal structure and morphology of these phasesi nt he literature. Previous work [42] was undertaken to identify these intermetallic phases by the electron backscatter diffraction (EBSD) technique, since EBSD is less ambiguous than metallographic methods and much more convenient than electron diffraction in TEM to surveyl arge numbers of particles.…”

Crystal structure and structural phase transitions in the GdBaCo2O5.0cobaltite

“…It is well recognized that joint powder and single-crystal diffraction techniques constitute a very powerful tool to achieve a high level of accuracy in crystal structure determinations. [42][43][44][45][46][47][48] It is therefore desirable to apply such approach when the expected changes in the crystallographic structure are hardly detectable.…”

Chinese Script vs Plate-Like Precipitation of Beta-Al9Fe2Si2 Phase in an Al-6.5Si-1Fe Alloy

“…The beta phase is considered to have a monoclinic crystal structure as shown in the studies by Romming et al, [8] Phragmen, [10] and Hansen et al [15] However, a conflicting result was obtained by Zheng [13] and Carpenter and Page [16] who indicated the beta phase as orthorhombic. Later work by Hwang et al [17] argues that this latter hypothesis was a misperception of crystal structure, so that the monoclinic structure will be accepted here.…”