Burgers vectors of dislocations in deformed iron and iron alloys

Abstract

A new two beam dark field electron microscope technique has been applied to the determination of the Burgers vectors of dislocations in thin foils of high purity iron, Fe-0-75 % Mn alloy and 2¼ % Cr-1% Mo steel. The experimental technique and the design of a new large angle tilt goniometer specimen stage are described. Specimens have been deformed over a range of temperatures from — 117 to 600 °C at strain rates between 0-18 and 15 % per hour. Relatively large proportions of a <100> and a <110> type dislocations in addition to the expected 1/2 a <111> type dislocations have been found and their screw-edge characters and directions investigated. The work has shown that the simple ideas involving only 1/2 a <111> type dislocations intersecting to form a <(100)> type junctions in body-centred cubic metals have to be considerably modified.