Formation of micrometer sized quasicrystals in slowly cooled Zr–Ti–Nb–Cu–Ni–Al alloys

The solidification behavior of copper mold cast Zr60Ti6Nb2Cu14Ni9Al9 and Zr60Ti2Nb6Cu14Ni9Al9 alloys has been investigated. The phase formation of the alloy with a ratio of Ti:Nb = 3:1 depends very sensitively on changes of the cooling conditions, exhibiting three competing phases: a glassy, an icosahedral quasicrystalline (i phase) and a crystalline phase, which are arranged very closely in the part of the sample with the highest cooling rate. Decreasing the cooling rate leads to a fully crystalline microstructure. In contrast, the alloy with a ratio of Ti:Nb = 1:3 forms predominantly an i phase and presents only a low volume fraction of a residual glassy phase at the interfaces of the quasicrystals. Besides a specific cooling rate a content of Cu + Ni + Al of about 32 at% and a content of Ti + Nb of about 8 at% is required for the formation of an as‐cast i phase in these Zr‐based alloys, because of a decrease of their glass‐forming ability linked with more pronounced icosahedral short‐range ordering in the melt. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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