Reactive Sintering of TiAl - Ti 5 Si 3 Lnsitu Composites

TiAl with between 0 and 20 volume percent (v%)Ti5Si3 was produced by reactive sintering of cofd pressed compacts of elemental Ti, Al and Si powder mixtures at 7OO0C for 15 minutes in vacuum. The results show that adding Si to Ti and A1 reduces the swelling associated with reactive sintering of TiAI, as composites containing more than 5 vYoTigSi3 densified during reactive sintering. However, composites containing more than 1Ov% Ti5Si3 did not retain their shape during processing, and the TiA1+20v% TisSiJ composite completely melted during the sintering process. A thermodynamic analysis indicated that the simultaneous formation of TiAl and Ti5Si3 increases the adiabatic flame temperature during the reaction between the powders. In fact, the analysis predicted that the maximum temperature of the reaction associated with the formation TiA1+20v% TisSi3 should exceed the melting point of TiAl, and this was observed experimentally. Differential thermal analysis (DTA) revealed that a AI-Si eutectic reaction occurred in mixtures of Ti, AI and Si powders prior to the formation of the TiAl and TiSSi3 phases. There was no such pre-reaction formation of an eutectic liquid in Ti and AI powder mixtures. The formation of the pre-reaction liquid and the increase in adiabatic flame temperature resulted in the melting that occurred and the enhanced densification (minimization of swelling) during reactive sintering of the insitu composites.