Multiphase transformations in undercooled melts

Kurzfassung

The current statements and novel results within the project MULTIPHAS (Non-equilibrium multi-phase transformations: eutectic solidification, spinodal decomposition and glass formation) are critically discussed in the present report. We describe and motivate experiments to be performed on board the International Space Station (ISS). Within the project, it is envisaged to measure the crystal growth velocity as a function of undercooling of intermetallic Cu50Zr50 and eutectic Cu56Zr44 alloy. Applying containerless levitation technique the intermetallic Cu50Zr50 alloy can be deeply undercooled (up to 310 K [1]), therefore, one may expect a serious influence of the temperature dependent diffusion coefficient and convective transport phenomena on the crystal growth kinetics. Also in the case of the eutectic Cu56Zr44 alloy, the growth kinetics is controlled by diffusion (at least at small and moderate undercoolings) and strongly dependent on convective transport occurring in the electromagnetic levitation facility. In addition to the problems in these binary alloys, the role of spinodal decomposition on the transition of the liquid to amorphous phase is investigated in Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 [2] and Pd40Cu30P20Ni10 alloys. Both alloys are belonging to bulk glass-forming alloys, which can be transferred to amorphous state by moderate cooling rates. The former shall be processed in the Electro-Magnetic Levitator (EML) currently under development by DLR/ESA within the COLUMBUS module of ISS while the latter one shall be studied using the Russian Multi Zone Electro Vacuum (MZEV) furnace currently under development by ROSKOSMOS on board the Russian module of the ISS. The transition “liquid state – amorphous state” especially is resolved by experimentation in microgravity and interpreted by theoretical modelling taking into consideration spinodal decomposition in the undercooled liquid prior to solidification. We acknowledge support from DFG (German Research Foundation) under the Project No. HE 160/19 and DLR Space Management under contract 50WM1140.