An experimental study of the mobility of edge dislocations in pure copper single crystals

Abstract

The velocity of edge dislocations in 99.999% pure copper crystals has been measured as a function of stress at temperatures from 66°K to 373°K by means of a torsion technique. The range of resolved shear stress was 0 to 15 megadynes/cm^2 for seven temperatures (66°K, 74°K, 83°K, 123°K, 173°K, 296°K, 373°K). Dislocation mobility is characterized by two distinct features: (a) relatively high velocity at low stress (maximum velocities of about 9000 cm/see were realized at low temperatures), and (b) increasing velocity with decreasing temperature at constant stress. The relation between dislocation velocity and resolved shear stress is: v=v_0(τ_r)/τ_0)^n, where v is the dislocation velocity at resolved shear stress τ_r, v_o is a constant velocity chosen equal to 2000 cm/sec, τ_0 is the resolved shear stress required to maintain velocity v_0, and n is the mobility coefficient. The experimental results indicate that τ_0 decreases from 16.3 × 10^6 to 3.3 × 10^6 dynes/cm^2 and n increases from about 0.9 to 1.1 as the temperature is lowered from 296°K to 66°K. The experimental dislocation behaviour is qualitatively consistent with an interpretation on the basis of phonon drag.

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