The effect of boron on the yield strength anomaly in FeAl single crystals

We report here results of tensile tests on FeAl single crystals oriented for single slip. B-free [3 (2) over bar1] and B-doped [8 (2) over bar3] Fe-43Al single crystals were tensile tested at temperatures from 77-1143 K. Optical microscopy showed the presence of straight slip lines parallel to one set of (110) planes on the gage sections of the B-free Fe-43Al specimens tested at temperatures below similar to1000 K, confirming that predominantly one slip system was active during deformation. In contrast distinct slip lines were observed in B-doped Fe-43Al only at 77 K, indicating more diffuse and homogeneous slip in this alloy. In the B-free alloy, the critical resolved shear stress (CRSS) decreased with temperature from 77 K to about 300 K, was only weakly temperature dependent from 300-700 K, increased to a peak at similar to900 K, and then decreased again with further increase in temperature. The B-doped alloy showed broadly similar trends. There was virtually no solid-solution strengthening due to boron at cryogenic temperatures and only modest strengthening in the region of the yield anomaly. However, boron did cause strengthening in the intermediate temperature range (250-700 K), and at high temperatures (beyond the yield peak).