When deformed in martensite state, NiTi undergoes pseudoplastic deformation taking place via motion of intervariant interfaces (called martensite reorientation or detwinning), followed by plastic deformation of the B19′ monoclinic martensite. The state of the art view is that: (i) the martensite reorientation proceeds via detwinning of <011> type-II twin laminates created by the martensitic transformation upon cooling and (ii) the reoriented martensite deforms plastically via dislocation slip. Although this view might be correct for single crystals and large grain size polycrystals, doubts existed whether it applies also for nanocrystalline NiTi which displays (001) compound twinned microstructures after stress free cooling from the austenite. The authors performed systematic experimental investigations of martensitic microstructures (postmortem TEM) and textures (in-situ HEXRD) evolving during tensile tests on nanocrystalline NiTi wires until fracture. The results indicate that the widespread view of the martensite reorientation as "detwinning" is incorrect. Plastic deformation of martensite proceeds via peculiar deformation mechanism involving (20-1) and (100) deformation twinning assisted by [100]/(011) dislocation slip. It enables the nanocrystalline NiTi wire to deform plastically at ~1 GPa engineering stress up to very large plastic strains ~50% and refines the austenitic microstructure down to nanoscale. Upon unloading and heating, reverse martensitic transformation takes place leaving large recoverable as well as unrecovered strains and high density of {114} austenite twins in the microstructure.

The scanning acoustic microscopy (SAM) technique is used for studying the character and interface quality of cold sprayed Fe coatings deposited onto notched Al-based substrates. Three notch geometries were used: a rectangular notch, a trapezoidal notch with a flat bed, and a trapezoidal notch with a cylindrical bed. Scanning electron micrographs demonstrated an increased porosity and cracks at the areas where the spraying direction was not perpendicular to the surface of the substrate. The SAM measurements were then performed on thin plates cut vertically across the notches such that the scanned area included the locations of the increased porosity and their surroundings. The resulting distributions of longitudinal wave velocities and their attenuation revealed that the affected area is more complex and the mechanical response of the coatings could be limited not only at areas of the visible porosity, but also in their vicinity.

Resonant ultrasound spectroscopy was applied to analyze the elastic anisotropy of thick copper, aluminum, titanium, and nickel coatings prepared by cold spraying and to determine the respective elastic moduli. The results show that the coatings exhibit only weak deviations from perfect isotropy, and the obtained elastic moduli are comparable with those of the corresponding polycrystalline bulks. The increased internal friction observed in some of the studied coatings may indicate grain refinement and consequent grain boundary sliding.