Mechanical Properties Of Ni/Cu And Ni/Amorphous Laminated Composites

Recently,ultrafine-grained metal and amorphous alloy have been studied extensively and understood well,because they have excellent properties,such as the high strength and high corrosion resistance,etc.However,it is found that the high strength material always has poor plasticity.Meanwhile,although the fatigue crack can not initiate easily in the high strength material,and thus improve the life of fatigue crack initiation stage,the propagation rate will be faster than that of corresponding coarse grain material once the crack initiates.In this study,two different laminated composites were designed to provide a new way to improve plasticity and fatigue properties of the high strength material.First,Ni/Cu laminated composites with four different thickness ratios of the Ni layer to the Cu layer were prepared using dual-bath electrodeposition technique.The grain size of the Ni layer in the composites is ultrafine grain,and the thickness of Ni layer is constant,the thickness ratio was controlled by changing the thickness of the Cu layer.Mechanical properties of Ni/Cu laminated composites with four different thickness ratios were investigated by tensile testing and fatigue testing at room temperature.Second,Ni layers with different thicknesses were electrodeposited on both sides of the Fe-based amorphous alloy ribbon with constant thickness to prepare sandwich-structured composites using the electrodeposition technique.Tensile and fracture behaviors of ultrafine-grained Ni/amorphous alloy/ultrafine-grained Ni sandwich-structured composites with different thicknesses Ni layer were investigated at room temperature.For the Ni/Cu laminated composites with four different thickness ratios,the result reveals that the Ni/Cu laminated composite with the thickness ratio of the Ni layer to the Cu layer is 9.0:1 not only has ultrahigh tensile(1360 MPa)and fatigue strength(350 MPa),but also has a good plasticity and an excellent fatigue ratio(the ratio of fatigue strength to ultimate strength).Under tensile loading,the thin Cu layers effectively delayed the local necking of the ultrafine-grained Ni layers,leading to more uniform deformation.Under fatigue loading,the introduction of the ultrathin Cu layers into the ultrafine-grained Ni layers led to the formation of step morphology in the process of fatigue crack propagation,the unique fatigue crack propagation path can maximize the cracking resistances in spatial directions,and improve the fatigue strength of composite.For the Ni/Fe-based amorphous alloy sandwich-structured composites with different thicknesses of Ni layers,the results indicate that the initiation and stable propagation of the shear band in the amorphous layer was dominated by the Ni layers due to their strong constraint role.In the composites,the constraint of both sides of Ni layers can effectively decreases the shear stress on the shear fracture planes of the amorphous layer,and the decrease in the shear stress becomes more pronounced with the increase in the Ni layer thickness.The decrease in the shear stress can promote the stable propagation of the primary shear band characterized by the variation in the smooth region size of the shear band.Therefore,the fracture of the amorphous alloy layer can be postponed and results in the increase in the plasticity of composites.