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Rapidly solidified Al–Cr alloys: Crystalline and quasicrystalline phases

Published online by Cambridge University Press:  31 January 2011

V. T. Swamy ,
S. Ranganathan  and
K. Chattopadhyay
V. T. Swamy
Affiliation:
Department of Metallurgy, Indian Institute of Science, Bangalore 560012, India
S. Ranganathan
Affiliation:
Department of Metallurgy, Indian Institute of Science, Bangalore 560012, India
K. Chattopadhyay
Affiliation:
Department of Metallurgy, Indian Institute of Science, Bangalore 560012, India
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Abstract

Rapidly solidified Al–Cr alloys up to 20 at. % Cr were studied to delineate the extent of crystalline and quasicrystalline phase formation in these alloys in comparison with as-cast alloys by using transmission electron microscopy and x-ray diffraction technique. The icosahedral quasicrystals are observed from 7 to 15 at. % Cr alloys, while equilibrium η–Al11Cr2 phase is completely absent. Both rapid solidification and subsequent thermal decomposition studies indicate that the main competing phase is θ–Al2Cr up to 15 at. % Cr. Beyond this composition ∊–Al4Cr is the dominant phase together with a small amount of γ4–Al7Cr3. We have shown that the electron diffraction patterns of Al–Cr quasicrystals are often associated with a diffuse intensity distribution, indicative of short-range order. The change in quasilattice constant with composition suggests the existence of structural vacancies. Further, a sudden change from coarse to ultrafine quasicrystalline grain structure in Al-7 at. % Cr alloy points to a change in nucleation mechanism from heterogeneous to homogeneous mode during the rapid solidification.

Type
Articles
Information
Journal of Materials Research , Volume 4 , Issue 3 , June 1989 , pp. 539 - 551
Copyright
Copyright © Materials Research Society 1989

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