Stress and Strain Partitioning of Ferrite and Martensite during Deformation

The direct measurement of the stress or strain partitioning during deformation in the materials, consisting of two phases with the same crystallographic structure and different microstructures, is still difficult so far. This is due to the fact that no effective characterization tool is available with the ability to distinguish the local strain and stress at microscale level. In this article, we studied the micromechanical behavior of ferrite/martensite dual-phase (DP) alloys using the in-situ high-energy X-ray diffraction (HEXRD) technique. We established a new method to separate the stress and strain in the ferrite and martensite during loading. Although the ferrite and martensite exhibit the same crystal structure with similar lattice parameters, the dependence of (200) lattice strains on the applied stress is obviously different for each phase. A visco-plastic self-consistent (VPSC) model, which can simulate the micromechanical behavior of two-phase materials, was used to construct the respective constitutive laws for both phases from the experimental lattice strains and to fit the macro-stress-strain curve. The material parameters for each phase extracted from our experiments and simulations could be used for designing other DP alloys and optimizing some complex industrial processes.