Improved corrosion resistance and surface stability of Mg–Ca alloys in simulated body fluid by quench-produced diamond coatings

Magnesium alloys are attractive biodegradable materials for biomedical implants; however, their clinical application is severely limited by rapid corrosion in physiological environments. In this study, Quench-produced Diamond (Q-Dia) films were deposited on Mg Ca alloy substrates at room temperature using the coaxial arc plasma deposition technique. Two surface pretreatments were employed prior to coating: (i) mechanical polishing and (ii) in-situ argon ion (Ar + ) etching, to clarify their influence on film formation and corrosion behavior. The surface morphology and bonding structure of the Q-Dia films were characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, revealing dense diamond-like grain growth with mixed sp 2 /sp 3 carbon bonding and a pronounced D-band feature. Corrosion performance was evaluated in simulated body fluid (SBF) at 37 °C using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP), with bare Mg Ca alloy as a reference. The Q-Dia coating significantly enhanced corrosion resistance, increasing the polarization resistance from 255 Ω.cm 2 to 2756 Ω.cm 2 and reducing the corrosion rate by more than one order of magnitude. In addition, tribological tests conducted in SBF demonstrated a stable and low coefficient of friction (~0.15), indicating improved surface integrity under wet sliding conditions. A comparative analysis revealed that Ar + etching is more effective than mechanical polishing in improving the structure, morphology, and corrosion resistance of the Q-Dia coatings. These results demonstrate that Q-Dia films act as an effective protective barrier against corrosive degradation, highlighting their strong potential as surface coatings for biodegradable Mg-based implant applications. • Quenched-produced diamond coatings were deposited on Mg-Ca alloys by CAPD. • Surface pretreatment strongly influenced coating morphology, adhesion and barrier properties. • Corrosion resistance in simulated body fluid increased by over one order of magnitude. • A low and stable friction coefficient was achieved under wet sliding conditions. • Improved corrosion and tribological performance indicate effective surface protection.