Containerless solidification studies in TiFeSiO and TiZrNi polytetrahedral phase-forming liquids

Icosahedral phase quasicrystals (i-phase) and related complex crystal phases (crystal approximants) form readily in many Ti/Zr-transition metal alloys. The relation between the local atomic structures of these polytetrahedral phases (i.e. ordered condensed phases that are dominated by local tetrahedral order) and the undercooled liquid is influential in quasicrystal formation and stability. To investigate this, undercooling studies were made on levitated droplets of TiFeSiO and TiZrNi alloys using electrostatic levtitation (ESL). Data from these studies are presented and discussed; comparisons are made with previously reported electromagnetic levitation studies of TiFeSiO alloys. Preliminary phase diagrams of both alloys, determined by a combination of ESL undercooling data and long duration annealing studies of as-cast samples, are presented and discussed. For TiZrNi alloys, these show unambiguously that the TiZrNi i-phase is thermodynamically stable, forming at low temperatures from a phase mixture of the C14 Laves phase and the (Ti/Zr)-Ni solid solution phase. The results of the ESL studies presented show that the reduced undercooling for crystallization decreases with an increasing polytetrahedral order of the primary solidifying phase, suggesting the development of icosahedral short-range order in the undercooled liquid.