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Laser shock processing, also known as laser shock peening, generates through a laser-induced plasma, plastic deformation and compressive residual stresses in materials for improved fatigue or stress corrosion cracking resistances. The calculation of mechanical effects is rather complex, due to the severity of the pressure loading imparted in a very short time period (in the ns regime). This produces very high strain rates (106 s−1), which necessitate a precise determination of dynamic properties.Finite element techniques have been applied to predict the residual stress fields induced in two different stainless steels, combining shock wave hydrodynamics and strain rate dependent mechanical behaviour. The predicted residual stress fields for single or multiple laser processes were correlated with those from experimental data, with a specific focus on the influence of process parameters such as pressure pulse amplitude and duration, laser spot size or sacrificial overlay.Among other results, simulations confirmed that the affected depths increased with pulse duration, peak pressure and cyclic deformations, thus reaching much deeper layers (> 0.5 mm) than with any other conventional surface processing. To improve simulations, the use of experimental VISAR determinations to determine pressure loadings and elastic limits under shock conditions (revealing different strain-rate dependences for the two stainless steels considered) was shown to be a key point.Finally, the influence of protective coatings and, more precisely, the simulation of a thermo-mechanical uncoated laser shock processing were addressed and successfully compared with experiments, exhibiting a large tensile surface stress peak affecting a few tenths of micrometres and a compressive sub-surface stress field.

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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. research papers J. Appl. Cryst. (2011). 44, 966-982 A. Baczmanski et al. Aged duplex stainless steel under deformation 967 research papers J. Appl. Cryst. (2011). 44, 966-982 A. Baczmanski et al. Aged duplex stainless steel under deformation 977 Figure 11Elastic lattice strains (h" TD i fhklg ) perpendicular to the loading direction (RD) versus the applied true stress AE RD for aged UR45N samples deformed in the tensile test. research papers J. Appl. Cryst. (2011). 44, 966-982 A. Baczmanski et al. Aged duplex stainless steel under deformation 981

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The double loop electrochemical potentiokinetic reactivation (DL-EPR) test using an electrolyte of 33 pct H 2 SO 4 solution with 0.3 pct HCl, at room temperature and at a potential scan rate dE/dt of about 2.5 mV/s, was chosen to evaluate the sensitization of austeno-ferritic duplex stainless steels (DSS). Reproducible and optimal test responses and high test selectivity in detecting intergranular corrosion (IGC) susceptibility were verified for four DSS differing in their method of fabrication (cast or wrought) and their ferrite phase content (44 to 57 pct). The test was successfully used to analyze the interactions between precipitation, chromium depletion, and IGC sensitization of the UNS S31250 steel, which was aged between 6 minutes and 120 hours at temperatures varying from 500 °C to 900 °C. The eutectoid decomposition of the ferrite, at different aging temperatures, was investigated using various techniques. The chromium depletion was analyzed qualitatively by X-ray mapping in a scanning transmission electronic microscope (STEM) and quantitatively by analytical calculation based on the chromium diffusion in the ferrite. It was shown that the chromium content in the ferrite can decrease from 30 to 7.5 pct by weight during aging before total decomposition occurs. The interactions between precipitation and IGC sensitization during DSS aging were clearly shown by superimposing the time-temperature-start of precipitation (TTP) and time-temperaturesensitization (TTS) diagrams obtained from the DL-EPR tests performed for various levels of sensitization.