TI5SI3 AND TI5SI3-BASED ALLOYS - ALLOYING BEHAVIOR, MICROSTRUCTURE AND MECHANICAL PROPERTY EVALUATION

Ti5Si3 is one of the candidate materials for very-high-temperature app lications. Alloying element additions such as Nb or Cr to Ti5Si3 resul t in alloys with different morphology and properties depending on the alloy design. The Ti5Si3-based stoichiometric alloys which can be abbr eviated as (Ti, M)(5)Si-3 where M = Nb, Cr, are composed of a monolith ic Ti5Si3 phase and are strengthened by solution hardening. Nb and Cr atoms dissolve in Ti5Si3 without changing its phase structure. The sol ubility of Nb or Cr in Ti5Si3 is determined to be at least 21 and 12 a l.%, respectively. The off-stoichiometric alloys, whose compositions a re Ti62.5MxSi37.5-x, display a hypereutectic microstructure with Ti5Si 3 as the primary phase. The brittleness of the off-stoichiometric allo ys is greatly improved compared with the stoichiometric ones. However, due to the weak phase involved, off-stoichiometric alloys appear to h ave low strength at high temperature and thus are unsuitable for very- high-temperature applications. (C) 1998 Acta Metallurgica Inc.