Quantitative analysis of stress/strain partitioning between soft and hard phases during deformation of multi-phased materials

Abstract

Under the growing demands of higher strength on structural materials, microstructures of advanced high-strength metallic alloys have become increasingly complex. The microstructures are in many cases composed of multi phases having different mechanical properties, i.e., strength and ductility. In the present study, we tackled to quantitatively evaluate stress/strain partitioning between hard phase and soft phase in multi-phased alloys using state-of-the-art experimental techniques. The micro-DIC (digital image correlation) analysis and neutron/synchrotron X-ray diffraction were applied to the dual-phase steels composed of soft ferrite and hard martensite phases for analysing strain and stress partitioning, respectively, between the phases during tensile deformation. From the average strain and stress amount in each of two phases obtained from the DIC and diffraction methods, we could reconstruct the stress-strain curves of ferrite and martensite separately for the Girst time. It was interestingly found that the stress-strain behaviour of two phases, especially that of the hard phase (martensite), greatly changed with increasing the density of inter-phase boundaries between two phases, leading to excellent strength-ductility synergy of the whole material having the particular morphology of the dual-phase microstructures. The result indicates that the deformation constraint through inter-phase boundaries plays a critical role to maximize deformation ability of hard phase(s) in alloys with multi-phase microstructures.