P. Rogl and A. Grytsiv
Inst. of Materials Chemistry, University of Vienna, A-1090 Wien, Austria
Socalled G-phases (Th6Mn23-type and ordered derivatives with Mg6Cu16Si7-type, all space group Fm-3m) constitute a large class of intermetallic compounds comprising aluminides, gallides, silicides, germanides and stannides.
Our systematic investigation (phase relations, X-ray single crystal structure analysis, neutron powder diffraction) of titanium based transition metal (TM) aluminide solid solutions Ti6{TM,Al}~23 however, revealed a filled variant of the Th6Mn23 type (space group Fm-3m) for the Al-rich single-phase region, whereas a novel structure variant with space group F-43m was established for the Ti-rich side of the G-phase region. The direct group-subgroup relation between space groups Fm-3m and F-43m may favour a second order phase transition.
In contrast to the various structure variants observed for titanium aluminium-based G-phases Ti6({Fe,Co,Ni,Ru,Rh,Pd,Os,Ir,Pt}1−xAlx)23+1 and Ti6Ni16+xSi7, the G-phase Mn6Ni16Si7 was confirmed to crystallize as a simple ordered variant of the Th6Mn23 structure type.
It should be noted that the ternary intermetallic G-phase silicide precipitates preferentially at grain boundaries and dislocations in both ferrite and austenite of duplex stainless steels and recently gained significant interest for ultra-high strength steels.
In view of applications, the presentation will provide a comprehensive overview on the structural chemistry of G-phases, particularly focusing on aluminides and silicides covering also stannides.
