Structure and properties of bioinert Mo – Nb coating formed on Titanium Grade 5 medical alloy by electroexplosive method

Abstract

In this article, an attempt was made to solve the problem of creating a coating for an implant that has better biological compatibility than the medical titanium alloy Titanium Grade 5. A Mo – Nb coating of the composition Mo – Nb is formed on the titanium grade 5 medical alloy by the electroexplosive method. The coating is formed as a result of the simultaneous electric explosion of molybdenum and niobium foils. A set of studies has been carried out to establish the structure, phase composition, and properties of the formed coatings. The coatings were studied by scanning and transmission electron microscopy. It is shown that the hardness of the surface layer of the coating by 60 % and Young’s modulus by 43 % exceed the corresponding characteristics of the Titanium Grade 5 alloy. The thickness of the layer with high (relative to the substrate) values of hardness and Young’s modulus reaches 80 µm. It was found that the wear parameter of the coating is 1.8 times, and the friction coefficient of the coating is 1.6 times higher than the wear parameter and the friction coefficient of the substrate. It has been established that in the surface layer, along with the coating atoms, there are Al, Ti, V atoms, which indicates that the coating is doped with substrate atoms, as well as oxygen and carbon atoms. The layering of the coating by elemental composition was revealed, namely, the top of the coating is enriched with niobium atoms, the lower part of the coating is enriched with molybdenum atoms. It is shown that the coating has a polycrystalline structure formed by a solid solution based on molybdenum. In the bulk and along the grain boundaries, there are inclusions of the second phase of the composition a-Ti, Nb, Mo9Ti4, and NbTi4 of various shapes and sizes. The studies of the phase composition did not reveal compounds based on vanadium and aluminum, which reduce the biocompatibility of the coatings. The identified phases contain only molybdenum, niobium and titanium, which are bioinert. This fact suggests that, as in studies of the phase composition of the surface of the coatings and its change in thickness, the biocompatibility of the obtained coatings will be higher compared to the Titanium Grade 5 titanium alloy. The conducted complex of studies makes it possible to recommend the resulting coatings for further clinical trials. These coatings are expected to be used in the future for better survival of titanium implants in the human body.