Tensile tests of Fe70Al30 in a TEM in the temperature range of the yield stress anomaly

Fe70Al30 is a long-range ordered material, which exhibits a yield stress anomaly. Thin single-crystal foils of Fe70Al30 have been strained inside a transmission electron microscope in the temperature range of the yield stress anomaly. The structure in this range is DO3. The dislocations had Burgers vectors parallel to the 〈111〉 directions and were predominantly of screw character. All dislocations were two-fold dissociated; no four-fold dissociations have been found. Below the peak temperature Tp glide on {110}-planes has been observed. The dislocations propagate by jumps. Once emitted from a source, they glide very rapidly over long distances before locking. In addition to glide on {110}-planes, close to Tp glide on {112}-planes has been observed. In these planes the glide is viscous. It is concluded that the anomalous temperature variation of the CRSS in Fe70Al30 can probably not be explained on the basis of the temperature dependence of the state of order.