Formation Mechanism of gamma/alpha(2) Full Lamellar in the New gamma-TiAl Alloy

Microstructural characteristics of TiAl-3Ta-x(Cr,W) alloy have been investigated in various annealing conditions, including cooling rates, heating temperatures and holding time by optics microscope (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the alpha(2)+gamma grains grow with longer heat treatment time while the fault and the dislocation are found in the full lamellar microstructure. The massive gamma precipitate in the microstructure by oil quenching and the full lamellar microstructure occurs by furnace cooling. Besides, the grain size of full lamellar is the smallest in the microstructure at the heat treatment temperature from T-alpha to T-alpha+20 degrees C, which is caused by weak beta stable element Ta.