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 transmi ssion electron microscopy in situ straining experiments: one dislocation so urce operates at wide interlamellar spacings by dislocation propagation in ferrite around cementite islands; the other consists of dislocations bulgin g in ferrite from interfaces, and is more likely to operate at narrow inter lamellar spacings. The constitutive law of the material is derived from a b alance between dislocation multiplication and annihilation rates, and predi cts a linear dependence of the flow stress with the reciprocal interlamella r spacing, and a stress saturation for very small spacings.