MICROSTRUCTURES OF TiAl BASED ALLOYS PREPARED BY HOT PRESSING ELEMENTAL POWDERS

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Elemental Ti, Al powders were hot pressed in Ar atmosphere at various temperatures in order to produce Ti 48Al (%) alloy. The microstructure evolution has been studied in this article through optical microscopy, scanning electron microscopy, EDAX analysis, X ray diffraction analysis and TEM observation. Results show that reaction between elemental Ti and Al is mainly controlled by diffusion. After hot pressing at 800 ℃, the reaction between Ti and Al powders is incomplete. The hot pressed microstructure mainly consists of Ti 3Al phase and TiAl phase. The higher the hot pressing temperature is, the higher the rate of reactive diffusion and the more complete the crystallization of TiAl and Ti 3Al will be. After hot pressing at 1 300 ℃, the Ti 3Al phase is island like. TEM observation shows that the island like Ti 3Al phase and the TiAl matrix are all composed of fine grains. After hot pressing at 1400 ℃, the microstructure consists of large γ grains and coarse lamellar microstructure. Therefore, 1 300 ℃ seems to be the premium temperature for reaction synthesis of TiAl based alloy.