Mechanical behavior anisotropy of multilayered metallic composites revealed by in-situ synchrotron X-ray diffraction: Example of Ti/Nb laminates processed by accumulative roll bonding

Abstract

Multilayered metallic composites have attracted widespread attention in both scientific and engineering communities owing to their exceptional mechanical properties. Clarifying the anisotropic mechanical behavior and the underlying deformation mechanisms is the premise for the successful application of those materials. In this study, the anisotropic plasticity and damage of multilayered Ti/Nb composites processed by accumulative roll bonding were investigated using synchrotron-based X-ray diffraction during tensile deformation. When comparing the uniaxial tension along rolling direction (RD) and transverse direction (TD), the laminates do not show obvious plastic anisotropy, but have significant anisotropic neck-to-fracture behavior. Residual stress, along with texture, contributes to the absence of anisotropy in yield strength. Under different loading directions, similar dislocation densities in each constituent metal, resulting from the similar grain morphologies, are responsible for the consistent ultimate tensile strengths. The collective hardening effect of the constituent metals results in the insignificant difference of work hardening in the bulk laminates. After necking, the faster degradation of mechanical property, namely the higher decreasing rate of flow stress, of the bulk composites loaded along the TD is attributed to the larger stress triaxiality of the Nb {211} grains (i.e. <211> // loading direction) that accelerates micro-void growth in the Nb layers as well as the more universal decohesion of hetero-interfaces between the different metals. These findings provide a comprehensive and in-depth understanding of the anisotropic plasticity and fracture behaviors, as well as the micromechanisms of Ti/Nb composites, which gives new insights to excavate the forming potential for multilayered metallic composites.