Intergranular Stresses and Micro-damage Process in Two-phase Materials Studied Using Diffraction and Self-consistent Model
Résumé
As a selective and non-destructive method, the diffraction method applied for in-situ tensile test is particularly useful in analysing the evolution of phase behaviour during elastic and elasto-plastic deformation of polycrystalline materials. This experimental technique enables determination of the mechanical properties for group of grains inside the gauge volume defined by diffraction condition. The measurements are carried out using selected hkl reflections during tensile/compression tests. In the case of multiphase polycrystalline materials, the measurement of separate diffraction peaks enables independent investigations of the mechanical behaviour of each phase.
In this work, a methodology combining diffraction experiments and self-consistent calculations was used to study behaviour of phases within two-phase polycrystalline materials (Al/SiCp composite and duplex austenitic-ferritic steel). Special attention was paid to the role of first and second order stresses on the yield stresses of the phases, as well as on the evolution of these stresses during the deformation process. The stresses were determined from lattice strains measured in situ during tensile tests and after sample unloading using neutron diffraction (JINR, Dubna, Russia and ISIS, RAL, UK) and diffraction of X-ray synchrotron radiation (ID15B, ESRF, Grenoble, France).
Comparison of the elasto-plastic self-consistent model with measured lattice strains allowed the determination of micro-mechanical properties of each phase in two-phase polycrystalline materials. The partitioning of the load between phases were correctly predicted by the self-consistent model. It was shown that the developed version of this model can be used to predict the consequences of damage processes occurring in a given phase.
The experimental and model results obtained in this work were used to study slip on crystallographic planes, localisation of stresses in polycrystalline grains and initiation of micro-damage occurring during plastic deformation.