ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The icosahedral quasicrystal has been found to appear in a wide composition range from about 5 to 16 at % Cr in rapidly quenched Al-Cr alloys, but the formation of the quasicrystal line single phase was limited only in the vicinity of about 15.5at% Cr. Analytical solute concentrations in the quasicrystalline phase are not always constant and increase continuously from 9.0 to 15.4 at% Cr with increasing nominal solute concentration from 6 to 15.4%. The quasicrystal can be approximately formulated to be Al11 Cr2 with a maximum deviation of about 6% Cr from the stoichiometric ratio to lower concentration side. Vickers hardness and electrical resistivity increase gradually with increasing chromium content and rapidly at about 14.5% Cr, and their values of Al84.6Cr15.4 quasicrystal are 710 DPN, 2.38μΩm at 4.2 K, and 2.72μΩm at 293 K. On the other hand, the onset transformation temperature of quasicrystal to crystalline phase,T t, and the heat of transformation, ΔH t show maximum values of 644 K and 1805 J mol−1 at 14.5% Cr and decrease to 625 K and 550 J mol−1 at 15.4% Cr. Al84.6Cr15.4 quasicrystal trans forms at two stages to a stable orthorhombic Al11Cr2 compound through a metastable intermediate phase with unidentified structure, while the quasicrystal + Al structure in Al-Cr alloys containing less than 15% Cr changes directly to stable phases of compounds and aluminium. The distinct difference in transformation behaviour of the quasicrystal is thought to be the reason for the abrupt changes inT t and ΔH t at a composition between 14.5 and 15.4% Cr.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01132404
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