ON THE MECHANISM OF EMBRITTLEMENT DURING AGING OF Fe-Al-Cr-Ti-Cu ALLOYS.

High purity Fe-5Al-7Cr alloys with 0. 7, 1. 4, or 2% Ti and 0. 7 or 1. 4%Cu were ductile on tensile testing 0. 05 in. sheet quenched from 870C but brittle after aging at 485 C. A variety of metallographic techniques were used to determine what changes in grain boundaries and matrices were responsible for the observed intergranular nature of the fractures. In the ductile as quenched condition, transmission electron microscopy revealed copious precipitates along with large quantities of dislocation tangles. In the brittle when aged alloys, almost complete pinning of dislocations by precipitates and fewer dislocations at grain boundaries were observed. Equilibrium segregation of elements to grain boundaries was slight and not consistent in the embrittled specimens. The Ti-Cu additions significantly improved strength properties in the solution treated condition but did not prevent embrittlement upon aging these ferritic alloys.