Surface mechanical attrition treatment (SMAT) was used to generate a gradient microstructure in commercial grade magnesium. Positron annihilation lifetime spectroscopy and variable energy positron beam measurements, as well as microhardness tests, electron backscatter diffraction, X-ray diffraction, and electrochemical corrosion tests, were used to investigate the created subsurface microstructure and its properties. It was found that SMAT causes an increase in dislocation density and grain refinement which results in increased hardness of the subsurface zone. The mean positron lifetime values indicate trapping of positrons in vacancies associated with dislocations and dislocation jogs. The increase of the SMAT duration and the vibration amplitude influences the depth profile of the mean positron lifetime, which reflects the defect concentration profile. Electrochemical measurements revealed that the structure induced by SMAT increases the susceptibility of magnesium to anodic oxidation, leading to the enhanced formation of hydroxide coverage at the surface and, as a consequence, to the decrease in corrosion current. No significant effect of the treatment on the residual stress was found.

Microstructural changes in grade 2 titanium generated by surface mechanical attrition treatment (SMAT) were studied using positron annihilation lifetime spectroscopy and complementary methods. A significant increase in the mean positron lifetime indicated many lattice defects introduced by SMAT. Two positron lifetime components were resolved in the positron lifetime spectra measured. The longer lifetime revealed the presence of vacancy clusters containing about 3 or 4 vacancies, while the shorter one was attributed to the annihilation of positrons trapped at dislocations. The changes of the positron lifetime indicated a decreasing dislocation density and the presence of a deeper layer with a higher concentration of vacancy clusters at the distance from the treated surface for which the microhardness approached the value for the strain-free matrix. Electrochemical impedance spectroscopy showed the positive effect of SMAT on the corrosion resistance of the titanium studied in a saline environment also after removal of the original oxide layer that was formed during the SMAT.

This chapter deals with the presentation of micromechanical modeling of the elastoplastic material behavior exhibiting ductile damage together with microstructural evolution in terms of grain rotation and phase transformation, under large inelastic strains. A description of the main experimental methods is proposed and multiscale measurements are discussed. For the mesoscopic scale, diffraction techniques are presented as well as microscopy’s results for a specific material. For the macroscopic scale, techniques of tensile test coupled with digital image correlation are described. This allows the damage measurement at different scales. Micromechanical modeling aspects based on the thermodynamics of irreversible processes with state variables defined at different scales are discussed. A non-exhaustive review of several possible models is given. These models depend on the hypothesis for the energy or strain equivalence and on the smallest scale considered. Two particular models are then detailed with their associated constitutive equations and the corresponding numerical aspects. Application is made to two different materials to test the ability of the model to be used for metal forming simulations.