Al-Fe-Ni-Ti: Phase Diagram Studies in TErnary Subsystems

For quite some time, intermetallic compounds have been considered for high-temperature structural applications. Among the compounds of interest, many involve aluminum as a main component. Usually, simple binary compounds are designed into actual engineering materials by further alloying with additional components in order to improve their service properties. Traditionally, such alloys were developed, more or less, by trial and error which can become quite time consuming and, as a consequence, expensive. Within the last twenty years, or so, modeling procedures have been developed which attempt to predict much more precisely the consequences of different alloying additions. Some of these modeling approaches are based on the so-called CALPHAD (Calculation of Phase Diagrams) method which allows to calculate phase diagrams based on optimized sets of Gibbs energy functions for all possible phases. Various extensions to this method provide today the possibility to predict, for example, the microstructure of the corresponding materials after a given heat treatment (Phase-Field Approach). The quaternary system Al-Fe-Ni-Ti is one of the most important aluminum-containing alloy systems, and it is clear that it will play an important role in the future for high-temperature structural materials. Therefore, it is the aim of the present project to provide experimental phase equilibria data for two of the ternary boundary systems, i.e. Al- Fe-Ni and Al-Fe-Ti, as input into CALPHAD-type phase diagram calculations. The European COST Action 535 ("Thermodynamics of Alloyed Aluminides - THALU") has identified a number of open questions in these systems that need to be clarified. Thermal analyses (DTA and DSC), powder X-ray diffraction and electron microprobe analyses will be used for the determination of phase equilibria in well-defined parts of the two ternary systems. If necessary, powder or single crystal X-ray methods may be used to refine the crystal structure of intermetallic compounds and their solid solutions. In addition, it will be attempted to contribute to the phase diagram calculations based on the CALPHAD- method in close cooperation with other partners within COST 535.