In situ dynamic observations of dislocation behaviour in metals and alloys by high voltage electron microscopy

In order to study the dynamical properties of dislocations, a new direct method is developed which is based on the in-situ deformation experiment in a HVEM. Various types of device for in-situ deformation of foil specimens under observation in a HVEM are developed. These devices allow the continuous recording of the dynamical behaviour of individual dislocations in the stressed crystals in the temperature range from 77K to 1123K, with the stress-strain curve being recorded simultaneously. The motion of edge and screw dislocations is observed in thick foil specimens of Fe, Fe-3%Si, Mo and Ni being stretched (or extended and compressed alternately) at various temperatures in a HVEM operated at 400 kV-1000 kV. By establishing a direct correlation between the dynamical behaviour of individual dislocations and the stress-strain behaviour of these crystals, the mobility, the multiplication and the interaction of dislocations are investigated. The strengthening mechanisms and the character of resistive forces which control principally the motion of dislocations in the different types of crystals (bcc or fcc) under the different experimental conditions (tension or compression, low or high temperature, irradiated or unirradiated etc.) are discussed.