MICROSTRUCTURE EVOLUTION OF RAPIDLY SOLIDIFIED TI3AL-2NB ALLOY

It has been found from the analysis of X-ray diffraction and the obser vation of TEM that the metastable ordered orthorhombic martensite alph a(0) '' phase in the rapidly solidified Ti3Al-2Nb alloy transforms to various phases at different aging temperatures. When the alloy aged at temperature of 500 degrees C for 20 min, the alpha(0) '' phase decomp osition into B2 and O phases is related to the stress in the alloy. Wh en the aged temperature above 600 degrees C, the alpha(0) '' phase tra nsforms to alpha(2) phase by both shearing and chemical ordering.