Texture Evolution And Deformation Mechanism Of Cu-Nb Multilayer Composites Fabrication Via Accumulative Roll Bonding

Multilayer composites have superior properties,such as high strength,high hardness,good thermomechanical stability and good resistance to radiation damage.These superior properties strongly depending on the prohibiting slip transmission of dislocations by the hetero-phase interface and texture component.Therefore,it is important to study the texture evolution and the influence of theinterface on the deformation mechanism,which providing experimental and theoretical data for further composite materials with high performances.In this study,Cu-Nb multilayer composites were fabricated by using accumulative roll bonded(ARB).In which the individual layer thickness varied from micrometer to sub-micrometer.The evolutions of microstructures with rolling cycle were characterized by electron backscatter diffraction(EBSD).The dislocation nucleation and motion,as well as crack propagation,were in-situ studied by a self-design TEM tensile device,which can be operated under the condition of biaxial tilts.These results provide experimental evidences for better understanding and designing of heterointerface for high performance materials.The main results are itemized as follows:(1)Cu-Nb layered composites with thicknesses ranging from 3.6 ?m ~100 nm were successful y prepared by ARB technique.With increasing rolling passes,the grains of both Cu and Nb were gradually elongated.After the fourth rolling,only 1~2 grains exist in a single layer along the thickness direction.(2)The grain orientations of Cu and Nb exhibit different evolutions from the first to the fourth rolling cycles.The grain orientations of Cu evolve from a dispersed distribution to {211}<0 1?1 >texture,whereas the grain orientations of Nb evolve from {211}<01?1> texture to {010}<101> and {111}<13?2> texture.(3)The grain orientation difference between the Cu and Nb layers in Cu-Nb layered composites shows a small angle distribution.This is consistent with the laws of small angle grain boundaries in rolled samples.(4)Through the in-situ tensile deformation,we observed that the grain boundary and phase boundary with high interfacial energy serve as the main source of dislocation.The dislocations first emit to the soft Cu layer and then slips in it.(5)Three types of dislocations nucleation and movement were observed in the Cu layer.The first type is that dislocation generated at the interface and slips into the Cu layer as the strain increases.The dislocation motion was blocked by the interface and then obstacle by the interface.For the second type,the both ends of dislocations were pinned by the interface and then slide along the interface as the strain increases.For the third type,dislocations nucleated at the interface,propagated towards the free surface,and annihilated at the free surface in the Cu layer with one side is the interface and the other side is the free surface.(6)The influence of two arrangement of Cu and Nb layers,i.e.,Cu-Nb-Cu and NbCu-Nb,on the fracture of the composite was studied.The fracture of N b layer all undergoes open fracture along the crack propagation direction in both of the two arrangements.The Cu layer shows different fracture behaviors under the two arrangements.For the Cu-Nb-Cu arrangement,Cu layer fractured along the interface.For the Nb-Cu-Nb arrangement,the Nb layer fractured first and its propagation was suppressed by the Cu layer.Therefore,the Cu layer sustains both uniaxial external stress and the shear stress of the Nb layer,which results in an internal shear fracture of the Cu layer.