EFFECT OF APB TYPE ON TENSILE PROPERTIES OF CR ADDED FE3AL WITH DO3 STRUCTURE

Fe-25 mol.%Al-2mol.%Cr, Fe-28mol.%Al and Fe-28mol.%Al-2mol.%Cr alloys were prepared in order to investigate the effect of Cr addition on ant iphase boundary (APB) types and tensile properties of D0(3) single-pha se Fe3Al polycrystals. The highest elongation and the lowest work-hard ening rate are obtained for Fe-28Al-2Cr. Fe-25Al-2Cr has the lowest el ongation and the highest work hardening rate. In addition to thermal A PBs, many uncoupled superpartial dislocations dragging extended APBs c an be seen in deformation microstructures for all the alloys. In Fe-25 Al-2Cr B2-type APBs are frequently observed with a small amount of D0( 3)-type APBs, whereas in Fe-28Al and Fe-28Al-2Cr all of thermal or def ormation-induced APBs are of D0(3)-type. Uncoupled superpartial disloc ations in deformed Fe-25Al-2Cr are blocked at thermal or deformation-i nduced APBs. By considering coordination configurations of neighbourin g atoms at an APE, the blocking force against dislocation motions is s hown to be higher for the B2-type APE than for the D0(3)-type APB. Thi s is related to the highest work-hardening rate of Fe-25Al-2Cr. In con trast, cross-slipping of uncoupled superpartials is more frequently ob served in Fe-28Al-2Cr than in Fe-28Al. The work-hardening rate of Fe-2 8Al-2Cr would be reduced by the occurrence of cross-slipping. Ductilit y improvement by the Cr addition is discussed in terms of an intrinsic change in the work-hardening rate of D0(3) Fe3Al alloys.