L. Le Joncour

Neutron time-of-flight diffraction used to study aged duplex stainless steel at small and large deformation until sample fracture

Owing to its selectivity, diffraction is a powerful tool for analysing the mechanical behaviour of polycrystalline materials at the mesoscale (phase and/or grain scale). In situ neutron diffraction during tensile tests and elastoplastic self-consistent modelling were used to study slip phenomena occurring on crystallographic planes at small and large deformation. The critical resolved shear stresses in both phases of duplex stainless steel were found for samples subjected to different thermal treatments. The evolution of grain loading was also determined by showing the large differences between stress concentration for grains in ferritic and austenitic phases. It was found that, for small loads applied to the sample, linear elastic deformation occurs in both phases. When the load increases, austenite starts to deform plastically, while ferrite remains in the elastic range. Finally, both phases undergo plastic deformation until sample fracture. By using an original calibration of diffraction data, the range of the study was extended to large sample deformation. As a result, mechanical effects that can be attributed to damage processes initiated in ferrite were observed.

Study of stress localisation in polycrystalline grains using self-consistent modelling and neutron diffraction

The time-of-flight neutron diffraction technique and the elastoplastic self-consistent model were used to study the behaviour of single and multi-phase materials. Critical resolved shear stresses and hardening parameters in austenitic and austenitic–ferritic steels were found by analysing the evolution of the lattice strains measured during tensile tests. Special attention was paid to the changes of the grain stresses occurring due to transition from elastic to plastic deformation. Using a new method of data analysis, the variation of the stress localisation tensor as a function of macrostress was measured. The experimental results were successfully compared with model predictions for both phases of the duplex steel and also for the austenitic sample.

Advanced Deformation Stages in Duplex Steel Investigated using Neutron and Synchrotron Radiation

Abstract The grain scale of materials is an area still open for investigations within the field of materials science. The most helpful tools to perform this type of research are diffraction methods. Within the research project presented in this paper two experiments were carried out employing two different types of radiation: neutron (ISIS) and synchrotron (ESRF). The aim of the work was to describe the stress state in the necking zone during the occurrence of a damage phenomenon (Fig. 1.) in separate phase and to check the level of the homogeneity. The supplemental tools were the finite elements method and self-consistent modeling – it testified, confirmed and completed our experimental results and allowed us to formulate the justifiable conclusions.