Abstract
The ductile-brittle transition of α-iron single crystals under a constant tensile stress is simulated by a molecular dynamics approach, focusing on thermal distribution in the crystals, where the Newton equations of motion are solved utilizing the Johnson potential. The simulation uses the ad-hoc velocity scaling method to control the crystal deformation at a low temperature, and showed brittle fracture starting at a notch in the plane perpendicular to the direction of stress. Another simulation where no scaling was used, and hence the temperature of the crystal increased during the deformation, showed plastic deformation at slip planes. From these two simulations, the brittle-to-ductile transition of α-iron can be explained by the temperature effect under deformation. With the use of a definition for local temperature at a nonequilibrium state, a substantial temperature increase was observed near the crack.
