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.

Aluminide coatings deposited by CVD method on CMSX-4 superalloy, modified by palladium and zirconium or hafnium as well as non-modified and palladium modif

This study investigates how surface modification of commercially pure magnesium influences the formation, microstructure, and long-term protective performance of phosphate conversion coatings (PCCs). An iron-free Surface Mechanical Attrition Treatment (SMAT) setup using zirconium dioxide balls of two diameters was employed to generate substantially different surface roughness while maintaining comparable subsurface modification, providing an experimental basis for isolating the effects of surface topography on PCC formation. PCCs were deposited on SMAT-treated and as-polished substrates and characterized using complementary microscopic, spectroscopic, and electrochemical techniques. The comparable subsurface modification but distinct surface topographies indicate that differences in PCC formation cannot be attributed solely to subsurface deformation. Instead, surface topography appears to influence coating nucleation and subsequent growth, with consequences for corrosion protection. SMAT pretreatment resulted in thinner, more uniform coatings composed of finer phosphate crystals. In contrast, coatings formed on polished substrates were more than twice as thick and exhibited inferior long-term corrosion performance, whereas those on SMAT-treated substrates remained highly stable throughout 28 days of immersion in 0.9 wt.% NaCl solution. These findings demonstrate that controlling magnesium surface state prior to phosphating enables tailoring of conversion coating structure and long-term protective performance.