Structure and Properties of Bioinert Mo–Nb Coating Formed on Titanium Grade 5 Medical Alloy by Electroexplosive Method

Abstract—An attempt was made to solve the problem of creating a coating for an implant having better biological compatibility than Titanium Grade 5 medical titanium alloy. A coating of Mo–Nb composition was prepared by the electroexplosive method on Titanium Grade 5 medical titanium alloy and formed as a result of the simultaneous electric explosion of foils made of molybdenum and niobium. A set of studies was carried out to determine the structure, phase composition, and properties of the prepared coatings. It is shown that the hardness of the coating surface layer is 60% and the Young’s modulus is 43% higher than the corresponding characteristics of 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 coating wear parameter is 1.8‑fold and the coating friction coefficient is 1.6-fold higher than the substrate wear parameter and friction coefficient. It was determined that, along with coating atoms, the surface layer comprises Al, Ti, V, O, and C atoms, indicating that the coating is doped with the substrate atoms. In the detected coating stratification by elemental composition, the top part of the coating is enriched in niobium atoms, and the bottom part is enriched in molybdenum atoms. The coating was shown to have a polycrystalline structure formed by a molybdenum-based solid solution. The bulk and the grain boundaries compose the second phase comprising α-Ti, Nb, Mo9Ti4, and NbTi4 of various shapes and sizes. The phase composition studies revealed no vanadium or aluminum compounds, which reduce the biocompatibility of coatings. The detected phases comprise only molybdenum, niobium, and titanium, which are bioinert, which allows predicting higher biocompatibility compared to the that of Titanium Grade 5 medical alloy. It is recommended to use the resulting coatings for further clinical tests.