EFFECTS OF ALLOYING ADDITIONS ON THE MICROSTRUCTURES, MECHANICAL-PROPERTIES AND WELDABILITY OF FE3AL-BASED ALLOYS

Several alloys based on the Fe-28Al-5Cr (atomic per cent) composition were produced to study the effects of alloying with Mo, Nb, Zr, B and C on microstructures, mechanical properties, and weldability. Optical microstructures were examined before and after heat treatments of 1 h at 750 degrees C, as well as after selected higher temperature anneals. Tensile properties at room temperature and 600 degrees C and creep-rupture properties at 593 degrees C and 207 MPa were determined and correlated with alloying additions. Judgments as to weldability of selected ahoy compositions were made by determining the hot-crack susceptibility. The results indicate that all of these properties of iron aluminides are very sensitive to alloying additions. Some combinations of the above elements resulted in re fined grain sizes, increased recrystallization temperatures, and strengthening of the base alloy (through solid solution effects, as well as the formation of precipitates) in both tension and creep-rupture tests. Increased strength, however, was generally produced at the expense of room temperature ductility and weldability. The results suggest that the design of useful iron aluminide compositions will depend on the application, with the composition being modified to provide either room temperature ductility and weldability or strength, as prescribed by the intended application.