Microscopic mechanism on the evolution of plasticity in nanolamellar γ-Ni/Ni5Zr eutectic composites

The evolution of microstructure and the mechanical properties of a series of (Ni0.912Zr0.088)100-xAlx (0≤x≤4) eutectic composites, constitute of γ-Ni and Ni5Zr nanolamellar phases, have been presented. Al dissolves in γ-Ni phase preferentially, decreases its hardness and refines the microstructure. Strain rate jump test was performed in order to investigate the rate sensitivity. It has been found that activation volume increases from 39b3 to 46b3 upon Al addition. The strain rate sensitivity of the composites has been estimated to be ~0.008. The scanning and transmission electron microscopic studies have confirmed that dislocation meditated flow in nano-lamellar phases dominates the plastic deformation mechanism. Analysis based on Stroh's pile-up model suggests that the required shear stress for slip decreases and that for cleavage crack nucleation increases around a dislocation pile-up at the lamellae interface, upon Al addition. The nano-lamellar Ni5Zr strengthen the composite, whereas, dislocation slip endorses the global plasticity of high strength Ni-Zr-(Al) nanoeutectic composites.