The plasticity of potassium

It has been known for a long time that the low-temperature deformation behaviour of potassium is very similar to that of the refractory b.c.c. metals. Therefore it is generally assumed that the same mechanism, namely kink-pair formation in screw dislocations, determines the deformation rate below a certain knee temperature Tk. A detailed investigation of the flow-stress of high-purity potassium single crystals showed that the knee-temperature is about 80 K, in contrast to values of 25–30 K reported in the earlier work. Between 80 and 4.2 K there exist three clearly distinct deformation regimes separated by bends or ‘humps’ in the curve of flow-stress versus temperature. A similar behaviour has been observed in the refractory metals. The close correspondence of these bends in b.c.c metals of radically different electronic structure strongly indicates that they are intrinsic properies of screw dislocation motion in the b.c.c. lattice and do not have their origin in details of the interatomic potential.