日本金属学会誌

J. Japan Inst. Metals, Vol. 54, No. 4 (1990),
pp. 427-434

Mechanism of Anomalous Temperature Dependence of Yield Stress by 11\={22}<\bar1\bar123> Secondary Pyramidal Slip in Cadmium Single Crystals

Shinji Ando1, Kazuki Takashima2 and Hideki Tonda2

1Graduate Student, Kumamoto University, Kumamoto
2Department of Materials Science & Resource Engineering, Faculty of Engineering, Kumamoto University, Kumamoto

Abstract:

The mechanism of anomalous temperature dependence of yield stress by 11\={22}<\bar1\bar123> second order pyramidal slip in Cd single crystals in proposed. (\mbic+\mbia) edge dislocations are immobilized as a result of thermally activated dissociation, i.e., (\mbic+\mbia)→>(\mbic sessile dislocation)+(\mbia basal dislocation). Increase in frequency of the immobilization with increasing temperature decreases the mean moving distance of (\mbic+\mbia) edge dislocations and consequently the amount of strain in slip bands. In order to maintain the constant strain rate at higher temperature, the velocity of slip band propagation by double cross slip of (\mbic+\mbia) screw dislocation to the next near slip plane must be increased by higher stress. Therefore, the yield stress increases with increasing temperature. The mean moving distance of (\mbic+\mbia) edge dislocation is nearly constant when the strain rate is increased. Then, the higher stress for increasing the slip band propagation velocity is needed to compensate for the increased strain rate. The yield stress, therefore, increases with increasing strain rate.
The negative temperature dependence of the yield stress below 133 K is considered to be caused by the deformation controlled by the Peierls mechanism.


(Received 1989/12/14)

Keywords:

cadmium, pyramidal slip, temperature dependence of yield stress, strain rate dependence, dislocation density, mean moving distance, dislocation immobilization, cross slip, activation energy


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