Effects of annealing temperature and layer thickness on hardening behavior in cross accumulative roll bonded Cu/Fe nanolamellar composite

Bulk Cu/Fe nanolamellar composites with different layer thickness were fabricated by cross accumulative roll bonding (CARB) technique. Here, annealing induced hardening and strengthening behaviors were observed in these composites as annealing temperature rises up to 400 °C. Especially, the increasing rate of strength and hardness are more remarkable in those with thinner layers. Then, mechanical properties gradually degrade after annealing at higher temperatures due to the destruction of layer structure. Detailed microstructural characterizations demonstrate that miraculous abnormal hardening of Cu/Fe nanolamellar composites induced by annealing is attributed not only to the density reduction of mobile dislocation inside heterogenic layers but also to the relaxation of non-equilibrium interphase boundaries. Furthermore, this phenomenon is closely correlated with the individual layer thickness, which is revealed by the diffusion effect of excess defects in the interfacial transition zones. •The hardening and strengthening behavior induced by low-temperature annealing is observed in Cu/Fe nanolamellar composite.•Interfacial transition zones (ITZs) could modulate interior microstructure and dislocations density during annealing.•This hardening rate is closely correlated with layer thickness due to the diffusion effect of excess defects in the ITZs.