Crystalline and quasicrystalline phases in rapidly solidified AlNi alloys

doi:10.1016/S1359-6454(96)00317-5

Acta Materialia

Volume 45, Issue 5, May 1997, Pages 2155-2166

https://doi.org/10.1016/S1359-6454(96)00317-5 Get rights and content

Abstract

The formation and structures of stable and metastable phases in splat-cooled AlNi alloys with 10–35 at.% Ni have been investigated by transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. The splats show a three-layer microstructure, the formation of which can be qualitatively explained by the assumption of a high undercooling of the melt prior to solidification. Two metastable phases—monoclonic Al₉Ni₂ and a decagonal phase—were found in the as-quenched alloys. Heat treatment leads to the decomposition of these phases, starting at the surface layer of the splat and continuing into the adjacent layers. In the alloy Al₈₅Ni₁₅, the Al₉Ni₂ crystals form during the recrystallization of the fine-grained surface layer. The electron diffraction patterns of partly transformed quasicrystals show strong diffuse intensities both perpendicular and parallel to the periodic direction. Structural relationships between the various phases are discussed.

Zusammenfassung

Das Vorkommen und die Strukturen stabiler und metastabiler Phasen in splatgekühlten AlNi-Legierungen mit 10–35 at.% Ni wurden mittels Transmissionselektronenmikroskopie, Röntgenbeugung and Differentialkalorimetrie untersucht. Die Splats zeigen ein aus drei Schichten bestehendes Gefüge, dessen Entstehung durch die Annahme hoher Unterkühlung der Schmelze vor der Erstarrung qualitativ erklärt werden kann. Zwei metastabile Phasen—monoklines Al₉Ni₂ und eine dekagonale Phase—wurden in den schnell abgeschreckten Legierungen gefunden. Wärmebehandlung führt zur Zersetzung dieser Phasen, die in der Oberflächenschicht beginnt und sich in den benachbarten Schichten fortsetzt. In der Legierung Al₈₅Ni₁₅ bilden sich die Al₉Ni₂-Kristalle während der Rekristallisation der feinkörnigen Oberflächenschicht. Die Elektronenbeugungsbilder teilweise umgewandelter Quasikristalle zeigen starke diffuse Intensitäten sowohl senkrecht als auch parallel zur periodischen Richtung. Strukturelle Beziehungen zwischen den verschiedenen Phasen werden diskutiert.

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Crystalline and quasicrystalline phases in rapidly solidified AlNi alloys

Abstract

Zusammenfassung

Scripta metall.

Mater. Sci. Eng.

Mater. Sci. Eng.

Mater. Sci. Eng.

Mater. Sci. Eng.

Mater. Sci. Eng.

Acta. metall. mater.

J. Non-Cryst. Solids

Acta metall.

Scripta metall.

Phil. Mag. B

Phys. Rev. Lett.

Phys. Rev. B

Phys. Rev. Lett.

J. Phys. F: Met. Phys.

Phil. Mag. Lett.

Z. Kristallographie

J. Phys. Soc. Jpn

Acta Cryst.

Phil. Mag. A

J. Phys.: Condens. Matter

Phil. Mag. B

Phys. stat. sol