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

The solidification behavior of copper mold cast Zr 60 Ti 6 Nb 2 Cu 14 Ni 9 Al 9 and Zr 60 Ti 2 Nb 6 Cu 14 Ni 9 Al 9 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)