Measurement of Instantaneous Dislocation Velocities in Iron

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9703993 Galligan In situ measurements of dislocation velocities and the associated mobile dislocation density are performed. These measurements, carried out while a metal crystal is deforming in an ordinary tensile test, are based on the intrinsic interactions of electrons with moving dislocations. The interaction can be varied by deforming a crystal in the presence of a rotating magnetic field, resulting in a change in the deformation stress. The change in stress occurs at an angle determined by the spatial orientation of the magnetic field vector relative to the moving dislocations. Measurement of the angle establishes the dislocation velocity of the mobile dislocations during an ordinary tensile test. Selective alignment and rotation of the magnetic field relative to the active slip system of the deforming crystal allows the determination of edge and screw dislocation velocities. These dislocation velocity measurements are carried out as a function of stress and temperature, establishing how the instantaneous dislocation velocity varies with these parameters. Dislocation velocities and mobile dislocation densities are also measured as a function of changes in the strain rate. %%% These experiments provide measurements of instantaneous dislocation velocities and mobile dislocation densities in iron crystals while they are deforming. This information is presently unknown for the plastic deformation of materials and provides the first such measurement in iron crystals. ***