ANALYSIS OF THE EVOLUTION OF ANTIPHASE BOUNDARIES IN A FE-AL ALLOY DURING IN-SITU TRANSMISSION ELECTRON-MICROSCOPY HEATING

In-situ heating experiments have been performed on thin foils of a sin gle crystal with composition Fe-25.6 at % Al. The isothermal evolution of antiphase boundaries (APBs) has been investigated by means of tran smission electron microscopy. APBs play an important role in phase cha nges of long-range ordered alloys. The grown-in domains were found to have the DO3 long-range order structure with randomly shaped APBs (swi rl-shaped domains). Up to 400 degrees C, no significant change in the domain and APE structure was observed. At 500 degrees C, which is belo w-the transition temperature. (T-c approximate to 550 degrees C) from DO3 to B2 coarsening of the domains has been analysed and dislocation motion was detected. The dislocations were analysed to have a Burgers vector of (a(0)'/4) (111) (a(0)' is the lattice parameter of the DO3 l attice). The dislocations drag behind them APBs of B2 type. Reactions of the B2-type APBs with the DO3-type grown-in boundaries have been an alysed. With increasing annealing time the density of the B2-type boun daries increases and the size of the domains becomes smaller. The asso ciated thickening of the B2 domain walls has been imaged.