Real space crystallography of a complex metallic alloy: high-angle annular dark-field scanning transmission electron microscopy of o-Al₄(Cr,Fe)

Abstract

High-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) has been performed along the low-index zone axes of the o-Al4(Cr,Fe) complex metallic alloy to obtain a real-space representation of the crystal structure and to elucidate the material's inherent structural disorder. By comparing experiments with multislice STEM simulations, the model previously suggested by X-ray diffraction is further refined to provide a new set of positions and occupancies for the transition metal atoms.Pmnbis suggested as the new space group for the o-Al4(Cr,Fe) phase. A nonperiodic layer-type modulation, averaged out in bulk diffraction methods, is detected, corroborating the need for complementing bulk diffraction analysis with real-space imaging to derive the true crystal structure of Al4(Cr,Fe).

Passivation/precipitation mechanisms of Al-Cr-Fe Complex Metallic Alloys in acidic chloride containing electrolyte

“…Aliquots of the solutions were sampled for ICPMS analysis after 1,4,7,14,22,28,42,56,78,105,155,189 and 269 days and subsequently diluted ten, hundred or thousand times with a 1% nitric acid solution (Suprapur grade, Merck, Germany). The dilution factors were chosen with regards to approximated sample dissolution rates obtained after preliminary analysis.…”

“…Al-Cr-Fe Complex Metallic Alloys (CMAs) are new intermetallic phases which present complex crystal structures with large lattice parameters (nm-size) and hundreds of atoms per unit cell [1], showing unique combination of bulk and surface properties, such as high electrical and low thermal conductivity, high hardness, low friction coefficient and good corrosion resistance [2][3][4]. The Al-based CMA are stable in a broad pH range (pH 0 H 2 SO 4 to pH 14 NaOH) [5], [6], thus, being promising as functional coatings for Al alloys and low alloyed steels.…”