A novel magnetically driven impact treatment for internal surface enhancement of titanium tubes

Achieving controllable impact-induced plastic deformation in geometrically confined internal cavities remains a fundamental challenge in advanced surface engineering. Here, a magnetically driven impact treatment (MDIT) is proposed as a model experimental platform, in which specially engineered magnetic core–shell shots driven by an external rotating magnetic field enable uniform and repeatable impacts on internal surfaces. In contrast to conventional techniques such as roller/ball-burnishing, ultrasonic shot peening, or surface mechanical attrition treatment, which are largely restricted to external surfaces and often deteriorate surface finish, the MDIT process developed here enables the simultaneous enhancement of surface hardness and surface finish. Experimental results on commercially pure titanium (CP-Ti) tubes show the formation of a surface gradient layer approximately 20–30 μm thick, with a 130 % increase in surface hardness and a tenfold reduction in surface roughness (Ra: 1.11 μm to 0.13 μm). Microstructural analysis reveals dense dislocation networks and deformation twins in the subsurface layer, indicating that twin–dislocation substructures, rather than grain refinement, dominate the strengthening mechanism. Real-time force monitoring confirms process stability with impact frequencies of ∼200 Hz. Beyond the specific configuration studied, the findings provide transferable insights into impact-based surface processing, with implications for strengthening and finishing different metallic materials, as well as tubular components used in aerospace, nuclear energy, and biomedical systems.