STUDY OF THE PHYSICOCHEMICAL PROPERTIES OF COATINGS FORMED BY MICRO-ARC OXIDATION ON A TITANIUM ALLOY

Abstract

This study investigates the physicochemical and mechanical properties of calcium phosphate coatings formed by micro-arc oxidation (MAO) on the titanium alloy Ti-13Nb-13Zr. The coatings were deposited in an electrolyte based on 30% H₃PO₄ with the addition of hydroxyapatite (60 g/L) and CaCO₃ (90 g/L) under various voltage, current, frequency, and processing time conditions. The microstructure and morphology of the coatings were investigated using optical and scanning electron microscopy (SEM/EDS). The coating thickness ranged from 68 to 162 μm depending on the micro-arc discharge (MAD) conditions. Surface roughness (Ra) was in the range of 7.99–12.06 μm and correlated with the intensity of the micro-arc discharges. Mechanical properties were determined using the instrumented microindentation method. The maximum values of microhardness (up to 420 HV), Young’s modulus, and yield strength were obtained for a sample formed at 500 V and 2 A. Scratch tests confirmed the high adhesive strength of the coatings and the absence of catastrophic delamination. Samples MAO_4–MAO_5 demonstrated the best combination of thickness, porosity, and mechanical stability. The results confirm the significant influence of micro-arc oxidation conditions on coating growth kinetics, the formation of a porous structure, and performance characteristics, which allows for the optimization of MAO parameters to produce bioactive and mechanically stable coatings for medical applications. Keywords: micro-arc oxidation, titanium alloy, Ti-13Nb-13Zr, oxide coatings, calcium phosphate coating, MAO, physicochemical properties, microhardness.