Formation Mechanism of γ/α2 Full Lamellar in the New γ-TiAl Alloy

Abstract:

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 α2+γ grains grow with longer heat treatment time while the fault and the dislocation are found in the full lamellar microstructure. The massive γ 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 Tα to Tα+20 oC, which is caused by weak β stable element Ta.

Key words:TiAl alloy; phase transformation; full lamellar microstructure