CRITICAL RESOLVED SHEAR STRESS OF LEAD

Abstract

Measurements of the critical resolved shear stress of lead are reported as a function of temperature, purity, solute additions, and orientation. By annealing in situ it was found that the value of the CRSS can be reduced, the scatter between specimens decreased, and the same specimen can be tested a number of times.Over the temperature range 4.2 °K to 600 °K (the melting point) the CRSS decreased from 53 g/mm2 to approximately 10 g/mm2. Between 100 °K and 300 °K the temperature dependence of the CRSS is the same as that of the shear modulus.It was found that the CRSS is relatively insensitive to differences in the trace impurity level and to solute additions of 0.1% Sn and 0.02% Cu. Additions of 1.0% Sn appreciably increase the CRSS at low temperatures.The orientation dependence of the CRSS is similar to that shown for copper, with higher values at the edges and corners of the stereographic triangle.Under optimum conditions the average value of the CRSS of lead is 34 g/mm2 at 78 °K. This value is anomalously high when compared to that of copper, using σ α [Formula: see text] for the flow stress to make the comparison.