Ultrafine-Grained Materials by Ruslan Z. Valiev & Igor V. Alexandrov & Megumi Kawasaki & Terence G. Langdon

Author:Ruslan Z. Valiev & Igor V. Alexandrov & Megumi Kawasaki & Terence G. Langdon
Language: eng
Format: epub
ISBN: 9783031317293
Publisher: Springer International Publishing

Fig. 3.13Surface of CG and NS samples of Grade 4 Ti after mechanical polishing and etching in the mixture of acids 30% HNOck.yt + 3% HF + H2O for 20 min: (a) CG Ti surface; (b) nano-Ti surface. SEM image. (Reprinted from [31], Copyright 2018, with permission from Elsevier)

The emission of Ti ions into the human body from UFG Ti implants is extremely low and much less than the histological level (level of presence of dangerous cells and neoplasms) established for Ti and equal to 5 ppm. By contrast, concentrations of Ti ions in the tissues surrounding CG Ti implants with grain size ≤1000 μm are usually much higher than in blood or saliva.

The deposition of biocompatible coatings on the surface of Ti implants and Ti-based alloys considerably increases the integration of implants and bone tissue [33–35]. At the same time, the actual problem is the synthesis of biocompatible coatings made from inorganic (Ca and P containing) and organic (containing bioactive and bioinert molecules) components on the implants. Biocompatible coatings contain hydroxyapatite (HA), which is the main crystalline component of human bone and a drug stimulant for osteosynthesis, but they obtain low adhesion to the Ti substrate as well as low mechanical strength. Plasma electrolytic oxidation (PEO) has recently been widely used for deposition of coatings containing Ca and P [33]. Application of this technique accompanied by high voltages contributes to microdischarges in the coating (Fig. 3.14a), its recrystallization, and intensive growth. The stable titanium dioxide modifications (rutile and anatase) are contained in the coatings. The deposition method featured by electrochemical oxidation and numerous melting and hardening of the microdischarged areas provides strong coupling to the surface. This method makes it possible to obtain the coatings with adjustable porosity and pore size from 0.1 to 10 μm (Fig. 3.14b) [34].

Fig. 3.14Images of microdischarges on the sample surface during the PEO process (a); SEM image of PEO Ca- and P-containing coating on titanium, top view (above) and cross-section (below) (b). (Reprinted from [31], Copyright 2018, with permission from Elsevier)

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