Zr Bearing γ-TiAl Induction Melted

Abstract

This paper describes the processing results of TiAl alloys melted under argon atmosphere by induction melting, using crucibles made of calcia and stabilized zirconia. Castings were allowed to solidify inside the crucible, in order to simulate the worst situation using this processing. Segregation profiles of residual elements and microhardness of different phases were evaluated, as well as its relation with the "alpha-case" extension.Two TiAl alloys, with 1 at. % zirconium and zirconium free, were produced and heat treated aiming to replace their as-cast structure by a quasi-lamellar one. The respective zirconium partition amongst microconstituents was evaluated, being demonstrated that zirconium concentrates in the γ-phase and increases the volume fraction of this constituent, showing the γ stabiliser role of zirconium.

The Production of TiAl by Foundry Processes

“…Although, in samples obtained in multi-layer crucibles, the volume fraction of interdendritic γ is smaller than that found in samples previously obtained in similar single-layer crucibles. This is due to the absence of residual Zr in the γ phase, which was found to stabilize that phase [8].…”

The characteristics of TiAl-based alloys melted in graphite crucibles

“…For this reasons, more and more often the attempts are made to use in the production of TiAl-based alloys the much cheaper technology of melting in induction furnaces with ceramic crucibles, which allows obtaining overheating at any level and which is widely used in the production of alloys of other metals. The research made so far has shown that the selection of suitable crucible material, charge form and reduction in the temperature and duration of melting can minimise processes resulting in the degradation of the crucible and uncontrolled transfer of its components to the liquid alloy [12–19]. The latest research of the authors of this study has shown that this is possible, for example in melting conducted in induction vacuum furnaces with special graphite crucibles [16,17,19].…”