| The changes in the microstructure, mechanical properties and DO₃↔ B2 transition temperature were investigated for Fe-25at.%Al alloys when Cr, Mo. Nb and B were added. As the amount of B addition increased, the grain size became smaller, the grain boundaries appeares clearer, and the amount of second phase precipitates increased. The DO₃↔ B2 transition temperature increased by about 70℃ with the addition of 2at.%oMo. Mechanical properties such as hardness(Rockwell & Microvickers) and yield strength were degraded by adding 6at.%Cr. The strength was increased by precipitate in the grains and along the grain boundaries with the addition of Nb. The Fe-25at.%Al alloy showed brittle cleavage fracture surface in the charpy impact test specimen. The addition of 6at.%Cr changed fracture mode from brittle cleavage fracture to transgranular cleavage fracture. When B was added, fracture occurred in transgranular dimple fracture mode. However, as the amount of Nb addition increased, crack propagated along the grain boundaries where brittle precipitates formed, showing intergranular fracture. |
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