NONEQUILIBRIUM ALPHA(2) GAMMA-INTERFACIAL STRUCTURES IN A GAMMA-TIAL BASED 2-PHASE ALLOY AFTER HOT-WORKING AND ANNEALING/

A transmission electron microscope investigation has been performed on the thermal instability of the nonequilibrium alpha(2)/gamma interfac ial structure in a hot-forged Ti-45Al-10Nb-2.5Mn-0.05B alloy. The dist inctiveness of these nonequilibrium alpha(2)/gamma interfaces in the h ot-deformed sample is the misorientation from the conventional orienta tion relationship {111}(gamma)//{0001}(alpha 2), <1(1) over bar0$>(gam ma)//<<11(2)over bar 0>>(alpha 2). The structure of this nonequilibriu m interface boundary is characterized by numerous interfacial ledges c ontaining 1/3[111] Frank partial dislocations. The analysis points tow ards the formation of this type of nonequilibrium alpha(2)/gamma inter face being caused by the relative rotation of alpha(2) and gamma plate s in the lamellar structure. Further TEM studies of microstructural ch anges during annealing for 4 min/1000 degrees C of the nonequilibrium alpha(2)/gamma lamellar structure generated by hot-forging revealed th at many low-angle grain boundaries are formed in the gamma plates of l amellar colonies, resulting in a gamma subgrain microstructure; neckin g of alpha(2) plates occurs preferentially at alpha(2) subgrain bounda ries; subsequently disintegration of the original alpha(2) plates take s place resulting in spheroidized alpha(2) particles which are aligned at the prior alpha(2)/gamma boundaries. (C) 1997 Published by Elsevie r Science Ltd.