Specific dislocation multiplication mechanisms and mechanical properties in nanoscaled multilayers: the example of pearlite

Dislocation mechanisms responsible for mechanical properties of nanoscaled multilayers are studied using the example of heavily drawn pearlitic steel wires. Two specific types of dislocation source are observed during transmission electron microscopy in situ straining experiments: one dislocation source operates at wide interlamellar spacings by dislocation propagation in ferrite around cementite islands; the other consists of dislocations bulging in ferrite from interfaces, and is more likely to operate at narrow interlamellar spacings. The constitutive law of the material is derived from a balance between dislocation multiplication and annihilation rates, and predicts a linear dependence of the flow stress with the reciprocal interlamellar spacing, and a stress saturation for very small spacings.