FLOW STRESS OF BODY-CENTRED CUBIC METALS AT LOW TEMPERATURES

Recent measurements on iron single crystals of 99·999% purity, containing less than 0·05 p.p.m. of carbon, show that the strong increase of the flow stress with decreasing temperature in the range 10-300°K is largely independent of small concentrations of interstitial impurities; it appears to be due to the Peierls force. Theoretical considerations employing the double-kink mechanism of dislocation propagation do not account satisfactorily for the observations. A new, simple, model is developed in which dislocation movement is induced by thermally activated formation of curved segments of dislocations trapped in Peierls troughs, the curvature being determined essentially by the effective shear stress. The predominant role of the shear stress in the determination of the curvature of the dislocation segment in the saddle-point configuration is the principal feature differentiating the present model from earlier double-kink treatments. Measurements made on iron and other body-centred cubic metals are successfully explained on the basis of the model.