Low-temperature dislocation absorption of ultrasound in high-purity α-iron single crystals. Effect of Peierls barriers and impurities on dislocation motion

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Abstract
The temperature and amplitude dependences of internal friction in as-grown, deformed and annealed high-purity α-iron single crystals are investigated in the temperature range 6–210 K. It was found that a small plastic deformation of samples (less than 1%) at room temperature leads to the appearance of relaxation peaks at 18 and 55 K in the temperature dependences of decrement, as well as to a sharp strengthening of the dependences of the decrement and modulus defect on the amplitude of an ultrasonic deformation over the whole temperature range. The height and position of the low-temperature internal friction peaks do not depend on the ultrasonic deformation amplitude. They also do not depend on whether they are measured in the linear or in the nonlinear regions of ultrasound absorption. After a long anneal, both peaks vanished and the amplitude dependences became weaker than those in untreated samples. It is shown that the effects observed arise because thermal activation overcomes the Peierls barriers and pinning at localized centres.