Interlayer Interface Architecture And Mechanical Behavior Of Nanolayered Cu/Nb And Cu/Zr Composites

There are abundant heterointerfaces in the nanolayered metallic composites because of its periodic alternating layered structure,and the grain size in its constituent layers is in the nanometer scale.This makes it show more excellent mechanical properties compared to the traditional bulk materials,such as ultra-high strength and hardness,good wear resistance,etc.Previous studies have shown that the heterointerface has a crucial effect on the mechanical behavior of nanolayered metallic composites with decreasing the feature size.Therefore,constructing nanolayer metallic composites with different types of interfaces and studying how they affect the mechanical response of the materials is beneficial to design the high-strength and high-toughness materials by adjusting the interfaces.In this paper,nanolayered Nb/a-Cu Nb,amorphous/gradient interlayer structure Cu/Nb and amorphous interlayer structure Cu/Zr were prepared by DC magnetron sputtering.The hardness and shear band behavior of nanolayered composites were studied by micro/nano indentation,and their corresponding deformation mechanisms were discussed.The results are as follows:(1)The hardness and shear band behavior of nanolayered Nb/a-Cu Nb composites exhibit strong size effects.When the layer thickness(h)is greater than 40 nm,the hardness of Nb/a-Cu Nb increases with the decrease of h and conforms to the traditional Hall-Petch model;when h continued to decrease(10 nm ? h ? 40 nm),the hardness continued to increase and could be explained by the confined layer slip model;however,when h is below 10 nm,the hardness of the composites will reach a peak value and its peak value is comparable to that of the amorphous Cu Nb film(8.45GPa).The results of microindentation show that the shear instability resistance of Nb/a-Cu Nb first increases and then decreases,and reaches the best at h = 40 nm.When the layer thickness is large(h > 40 nm),Nb/aCu Nb produces a sharp shear band along the shear plane and shows gradually increasing resistance to shear instability.This is mainly because the reduction of stress concentration induced by the dislocations pile up is not conducive to the nucleation of shear bands.When the layer thickness is small(h < 40 nm),Nb/a-Cu Nb generated shear bands induced by the bending of synergistic layer and the degree of shear instability gradually increased.This is because the decrease of h leads to more active grain boundary motion(grain rotation and grain boundary slip)in Nb layer,which eventually increases the shear instability.When h = 40 nm,the shear instability of Nb/a-Cu Nb is suppressed to produce uniform co-deformation.This is because the confinement layer slip deformation mechanism and shear transition zone are activated in Nb and a-Cu Nb layer,respectively.(2)The hardness results of the amorphous/gradient interlayer structure Cu/Nb show that the hardness of it is slightly higher than that of the homogeneous Cu/Nb when the amorphous interlayer is introduced,while the hardness is almost unchanged when the gradient interlayer is introduced.This indicates that the introduction of an interlayer in homogeneous Cu/Nb with a layer thickness of 50 nm has a limited effect on the hardness.The indentation results show that with the increase of the thickness of introduced amorphous interlayer,the number of shear bands in the composites increases and the strain of layer in shear region is larger and more concentrated.When the gradient interlayer is introduced,the number of shear bands is less than that of the 50 nm homogeneous Cu/Nb and the strain of layer in shear region is smaller.This shows that the introduction of different types and thicknesses of interlayers has a significant effect on the shear behavior of the nanolayered composites.Compared with the homogeneous Cu/Nb,the gradient interlayer structure Cu/Nb can obtain more excellent resistance to shear instability without reducing the hardness.This is because the introduction of an interlayer with a composition gradient can reduce the abrupt change between microstructure and properties of the constituent layers,thereby reducing the stress concentration near interface and improving the shear instability resistance of composites.(3)The hardness results of amorphous interlayer structure Cu/Zr show that the hardness decreases when the thickness of amorphous interlayer decreases from 10 nm to 5 nm,while the hardness increases when the thickness is further reduced to 2 nm.The indentation results show that the amorphous interlayer structure Cu/Zr produces multiple shear bands both along the extrusion direction and in the depression direction of the indentation.This difference in shear deformation characteristics may stem from the fact that the thickness of amorphous interlayer affects the ease of shear band nucleation.