Mechanical Properties of Metals at Low Temperatures

Abstract

There are interesting differences in the temperature dependence of the mechanical properties of f. c.c. (face centered cubic) and b.c.c. (body centered cubic) metals. The flow stress of f.c.c. metals increases moderately as the temperature is lowered, but the rate of work hardening is much greater at low temperatures than at normal temperatures. In b.c.c. metals, there is a very marked increase in yield stress with decreasing temperature but the work-hardening is not very temperature sensitive. According to present ideas, the temperature dependence of the mechanical properties may arise in two different ways. The motion of a dislocation is opposed by internal stresses arising from other dislocations, impurity atoms in solution etc., and insofar as these stresses vary with temperature, they will contribute directly to the temperature variation of the yield and flow stresses. During deformation, moving dislocations are occasionally halted by “obstacles” which produce short range interactions of appreciable magnitude. The motion of the dislocation is resumed when the obstacle is surmounted under the combined influence of the stress acting on the dislocation and the thermal energy of the lattice.