抄録
Twinning behaviour of tin was investigated as a function of temperature and strain rate. The resolved shear stress for twin became large and the scatter of individual values was pronounced, as the temperature was lowered and strain rate was increased. The observed twinning stress was not so large as to expand the stacking-fault across the crystal, but it was sufficient to trigger twin nucleus if local stress concentration was produced, say, by dislocation pile-ups. As the temperature was raised and strain rate was decreased, deformation by slip preceding twin became dominant, and twin formation was finally prohibited. The activation energy derived from the ductile-brittle transition temperatures is approximately that of self diffusion, suggesting that recovery due to dislocation climb releases local stress and prohibits twin nucleation. Hardening of twin boundary migration was found at low temperatures or at high strain rates, while the initial migration stress was not raised by these factors but raised by prestrain. It was about one order of magnitude smaller than that for twin initiation, and too small for the creation of twin dislocation ring on the existing twin layer. A mechanism of sweeping and climbing of the twin dislocation around a pole dislocation is necessary to explain the observedvalue.
