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[Display omitted] • Severe plastic deformation behavior of AM repaired Ti-6Al-4V alloy samples subjected to LA-UNSM treatment was thoroughly investigated. • Sufficient grain refinement, with a mix of elongated and ultra-fine grains, was produced on the surface of the LA-UNSM sample, eliminating larger columnar grains. • Improved roughness, hardness, compressive stress, and fatigue life were achieved after LA-UNSM treatment. • Fatigue life was enhanced by LA-UNSM's work hardening and dynamic precipitation effects. Ultrasonic nanocrystal surface modification (UNSM) combined with localized laser heating (LA) were implemented to enhance the surface fatigue life of additively repaired Ti-6Al-4V alloy parts in this study. The effect of induced surface severe plastic deformation on microstructure development and grain refinement is analyzed. The results showed that surface metallurgical defects, hardness, residual stress, and roughness were significantly improved after LA-UNSM treatment. As a result of the improved surface textures and higher grain refinement, the fatigue life of the LA-UNSM treated samples was an order of magnitude longer. Surface free of pores and displaying a healthy topography provides evidence. [ABSTRACT FROM AUTHOR]

[Display omitted] • UNSM refined the martensite laths and formed a plastically deformed layer on A100 steel. • Higher surface hardness and higher fretting wear resistance were observed. • High magnitude compressive residual stresses were generated in the near surface region. • Both the plain fatigue and fretting fatigue resistance of A100 steel were improved. In this study, ultrasonic nanocrystal surface modification (UNSM) was used to improve plain and fretting fatigue properties of A100 steel. Results showed that an obvious plastic deformation layer was induced in A100 steel, and the martensite microstructure was remarkably refined. In addition, surface compressive residual stress after UNSM treatment was enhanced to 1700 MPa due to the severe lattice distortion. The increased surface hardness and the presence of beneficial compressive residual stresses after UNSM treatment significantly enhanced the plain/fretting fatigue resistance of A100 steel by retarding fatigue crack nucleation and propagation. [ABSTRACT FROM AUTHOR]