Solidification behavior of Ti5Si3 whiskers in TiAl alloys

The solidification behavior of Ti52Al48–xSi (x=0, 0.5, 1.0, 2.0, 3.0, 6.0 at.%), Ti52Al48–3Si2M (M=Cr, V) and Ti52Al48–3Si2Cr2V at.% alloys has been studied using differential thermal analysis (DTA) and microstructure examination. The Ti5Si3 phase was formed during solidification of the Si containing TiAl alloys. Two types of Ti5Si3 phase were found in Ti52Al48–xSi (x=0.5, 1.0, 2.0 at.%). The first one was formed during the L→Ti5Si3+L1 transformation as large isolated Ti5Si3 whiskers formed before primary solidification, and the second one was characterized by whiskers in a eutectic morphology resulting from the solidification of L2→α+Ti5Si3 after the primary solidification of L1→β+L2. In contrast, the primary solidification in the Ti52Al48–3Si alloy was L1→α+L2, and a third type of Ti5Si3 phase was formed by a eutectoid reaction of α→γ+Ti5Si3. The effect of Cr and V on the solidification behavior and constituents of the Ti5Si3 phase were studied with distributed coefficient of Cr, V, and Si. The uniform distribution of fine Ti5Si3 whiskers in the Ti52Al48–3Si2Cr2V alloy gives effective reinforcement of the matrix.