High temperature phase diagram near thestoichiometric composition of TiAl alloys could be accuratelyestablished by directional solidification. From the results on theanalysis of quenched dendrite morphologies of Ti-44Al and Ti-52Al(at.%), it was found that the β and α phases were formedas the first solidified phase, respectively. Thus, it was concludedthat β+γ two phase region which Murray suggested does notexist. Considering the results on the EDS analysis of the quencheddendrite tips and the measurement of temperature gradient directlyrecorded during directional solidification process, hightemperature phase diagram of Ti-44, 46, 48, 50, 52 at.%Al alloycompositions was established. Liquidus temperatures ofcompositions selected were inspected by DTA. This result agreedwith the phase diagram that Okamoto proposed. From the aboveresults, the composition in which liquid phase was fullytransformed to β phase could be determined. To confirm thephase diagram completed by this study, the directionalsolidification of Ti-44at.%Al was performed at the growth rate of45mm/hr. It was found that the lamellar orientation was alignednearly 0 to 45° to the growth direction. It was thought that theabove results were due to β solidification of Ti-44at.%Al alloyat the beginning of liquid/solid transformation.
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