Burgers vectors of dislocations in deformed iron and iron alloys

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$\cdot$75% Mn alloy and 2$\frac{1}{4}$% 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 $^\circ$C at strain rates between 0$\cdot$18 and 15% per hour. Relatively large proportions of a$\langle100\rangle$ and a$\langle110\rangle$ type dislocations in addition to the expected $\frac{1}{2}$a$\langle111\rangle$ type dislocations have been found and their screw-edge characters and directions investigated. The work has shown that the simple ideas involving only $\frac{1}{2}$a$\langle111\rangle$ type dislocations intersecting to form a$\langle100\rangle$ type junctions in body-centred cubic metals have to be considerably modified.