Relationship of the Structure and the Effective Diffusion Properties of Porous Zinc- and Copper-Containing Calcium Phosphate Coatings

Abstract

The morphology and the structure of zinc- or copper-containing calcium phosphate coatings deposited by the microarc oxidation (MAO) method at different voltages on pure titanium and low-modulus Ti-40 wt % Nb alloy substrates are investigated. The morphology of the MAO coatings on both substrates is composed of sphere-shaped structural elements 8–42 μm in size and pores 1–15 μm in size. When the process voltage is increased from 200 to 300 V, these structural elements grow and partially destruct. It is ascertained that the MAO voltage increase leads to the linear increase in the surface porosity of the coatings from 14 to 24%. It is established that the effective diffusion coefficients of the model biological fluid in porous coatings vary from 0.85 × 10^–10 to 9.0 × 10^–10 m²/s. Under the increase in the structure element size, the effective diffusion coefficient of the model biological fluid increases in the MAO coatings deposited on a titanium substrate and decreases in those deposited on Ti-40 wt % Nb alloy. The observed difference is related to the increase in the crystalline phase fraction.