Mechanistic investigation of chemically assisted magnetic compound fluid polishing of titanium capillary tube inner surfaces

The inner surface quality of titanium capillary tubes is directly linked to the precision and reliability of associated biomedical devices. However, the chemical stability of titanium and the spatial constraints of capillary structures present significant challenges for inner-surface finishing. In this study, the chemically assisted magnetic compound fluid (CAMCF) polishing process was systematically investigated with a focus on its underlying mechanism. This process couples abrasive motion under an applied magnetic field with in-situ chemical reactions triggered by hydrogen peroxide (H₂O₂) and malic acid (MA), enabling synergistic surface softening and material removal. Combined-condition and single-variable experiments were conducted to systematically evaluate the effects of H₂O₂ and MA concentrations on surface roughness Ra and material removal rate (MRR, defined as the removed material volume per unit time, μm³/h). Under optimized conditions (7.2 wt% H₂O₂ and 5 wt% MA), the CAMCF process achieved a maximum MRR of 42.78 μm³/h, reducing the surface roughness from Ra 3.10 μm to Ra 65.3 nm. To elucidate the material removal mechanism in CAMCF processes of titanium, a series of characterization techniques were employed, including surface morphology observation, static etching, Raman spectroscopy, and nano-scratching tests. Results revealed that under synergistic chemical conditions, a porous and structurally weakened titanium oxide film was formed on the surface, exhibiting reduced mechanical strength and facilitating brittle fracture and efficient removal by abrasive particles. Based on these findings, a dynamic “oxidation–complexation–removal–regeneration” mechanism is proposed, which effectively describes the coupling among surface modification, oxide layer renewal, and mechanical abrasion. This mechanistic perspective constitutes the main originality of this work, providing fundamental understanding for CAMCF process optimization and offering guidance for the development of high-precision polishing techniques for the inner surfaces of titanium capillary components.