On the peritectoid Ti3Si formation in Ti-Si alloys

Ti-13DDT5Si and Ti-25Si (at.%) alloys have been arc-melted from high-purity raw materials, using a water-cooled copper hearth, a non-consumable tungsten electrode, and under an Ar atmosphere gettered by titanium. The cast ingots were then heat-treated for 90 h at 1000 and 1100 DDGC in an inert atmosphere, and both the as-cast and the heat-treated alloys were characterized using scanning electron microscopy and an energy dispersive microanalysis system. The as-cast Ti-13DDT5Si alloy presented a eutectic microstructure composed of the TiSS and Ti5Si3 phases, while the microstructure of the as-cast Ti-25Si alloy showed the presence of large primary precipitates of Ti5Si3 in a eutectic matrix of TiSS and Ti5Si3. Subsequent heat treatment at 1100 DDGC produced no significant microstructural modifications in the Ti-25Si alloy, and it is suggested that the presence of the large primary precipitates of Ti5Si3 contributed to a reduction in the kinetics of Ti3Si formation. In the Ti-13DDT5Si alloys, the formation of Ti3Si was not observed after heat treatment at 1000 DDGC, but a large amount of Ti3Si was found after heat treatment at 1100 DDGC, confirming its existence in Ti-Si alloys containing low interstitial contents.