The effects of Cr and W on mechanical properties and microstructures of Fe-26.5at.% Al intermetallic compound were investigated by optical microscopy, X-ray analysis, tensile testing, SEM, and TEM analysis.
It has been found that the addition of Cr or W to Fe-26.5 Al increased the $D0_3$-B2 transition temperature. The results showed that W was more effective than Cr on increasing transition temperature. The Cr addition did not induce grain size refinement, but it promoted $D0_3$ domain growth. On the other hand, the W addition decreased not only grain size but also $D0_3$ domain size.
The variation of yield stress with temperature in the binary Fe-26.5 Al did not exhibit an anomalous yield stress variation by the change in the degree of order. However, either Cr or W added Fe -26.5 Al-X alloy showed an anomalous variation of yield stress with temperature; the yield stress increased with the increased temperature. The results may be attributed to the fact that the glide mode of superlattice dislocation was changed by the variation of the antiphase boundary energy among the next nearest neighbor atoms and antiphase boundary energy among the nearest neighbor atoms with Cr and W addition to Fe-26.5 Al.
In the tensile test at R.T., Fe-26.5 Al alloy containing only Cr showed about 3~4% elongation, and Fe-26.5 Al alloy containing both Cr and W as well as Fe-26.5 Al showed about 5~6% elongation. The fracture mode of the all alloys were transgranular cleavage at room temperature. But some dimple mode was observed at 300℃ and completely dimple mode at above 400℃. In the tensile testing from 300 to 650℃, the Cr addition decreased yield strength in all temperature range. The W addition was beneficial and increased the yield strength.
