Low-temperature plasticity of bismuth single crystals

A study is made of the effect of temperature on strain hardening and slip propagation in bismuth at 4.2, 77.3, 130, and 293°K. At low temperatures the dependence of deforming stress τ on shear strain ϵ is exponential, and no relaxation of the flow stress τ0 is observed. The temperature dependence of the flow stress τ0(T) is nonmonotonic, with a maximum at 130−160°K. The magnitude of the relative shear in the slip bands increases by a factor of around 10 as T decreases from 293 to 4.2°K, although τ0 at this temperature is the same. A theoretical description of low-temperature strain hardening of bismuth is given using an exhaustion model of slip-band sources. The distribution function of the number of sources over start stress is recovered through the form of the curve τ(ϵ) and data on the width of the slip bands and their relative shear. At low temperatures nucleation of dislocation loops on heterogeneities is nonactivational in nature. It is shown that the mean velocity of dislocations at the flow point in bismuth increases with decreasing T from 293 to 4.2°K. The nature of the nonmonotonic dependence τ0(T) is discussed.

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