Irina P. Semenova

Nanostructured SPD Processed Titanium for Medical Implants

Nanostructured titanium (nTi) with essential enhanced strength and fatigue characteristics is an advanced material for dental implant applications. Nano Ti is commercially pure titanium, that was nanostructured by a special technique of severe plastic deformation. It is bio inert, does not contain even potentially toxic or allergenetic additives and has significantly higher specific strength properties than any other titanium applied in dental implants. Cylindrical threaded screw implants Nanoimplant® sized 2.4 mm in diameter and 12 mm in length were made from nTi. It is the first application of nTi dental implant in the world reported. Recently more than 250 successful clinical applications dealing with surgery on the front teeth were carried out. No complications were noticed during the early postoperative period and early loading. Laboratory cytocompatibility tests undertaken so far on mice fibroblast cells have indicated that nanocrystalline Ti surface has a significantly better property for cell colonisation and healing of tissue consequently.

Nanostructured titanium for biomedical applications: New developments and challenges for commercialization

In this paper, the scientific basics for the production of nanostructured titanium using the technology of severe plastic deformation to manufacture medical implants for their wide use in trauma treatment, orthopaedics, and dentistry are presented. Special attention is paid to the physics and mechanics of methods of severe plastic deformation leading to the formation of nanostructured states in titanium. The influence of nanostructuring on the mechanical and biomedical properties of titanium is studied, and the advantages of applying nanostructured titanium for medical implants are considered in detail. Methods for commercialization of this new material are discussed in detail. An important step is the creation of the pilot commercial production of semiproducts, rods from nanostructured titanium with a length of more than 3 m and a diameter of 5–8 mm, for an annual production volume of 2 t.

Nanostructuring of Ti-alloys by SPD processing to achieve superior fatigue properties

Abstract This work is related to the enhancement of the fatigue properties in ultrafine-grained Ti alloys produced by severe plastic deformation techniques. To process commercially pure Ti Grade 4 and Ti-6Al-4V alloys, combined severe plastic deformation techniques that include equal channel angular pressing and additional thermal and deformation treatments were used. As a result we could produce ultrafine-grained Ti materials with a similar grain size of less than 300–400 nm but different in their shape and grain boundary structure (both low- and high-angle, equilibrium and non-equilibrium grain boundaries). It is shown that tailoring grain boundaries by severe plastic deformation techniques makes it possible to considerably enhance the strength of Ti materials while preserving high ductility. In turn, ultrafine-grained materials with enhanced strength and ductility demonstrate superior fatigue endurance and life.

Microstructure and Properties of Ti Rods Produced by Multi-Step SPD

This paper studies the effect of combined SPD treatment on microstructure and mechanical properties of semi-products out of CP Ti. The combined processing, consisting of equal-channel angular pressing and further thermomechanical treatment, produced ultrafine-grained rods out of Grade 2 CP Ti with a diameter of 6.5 mm and a length of up to 1 m. It was established that the formation of homogeneous ultrafine-grained structure in Ti rod with α-grain size of about 100 nm allowed to enhance yield stress by 200% in comparison with initial annealed state.

Microstructural Features and Mechanical Properties of the Ti-6Al-4V ELI Alloy Processed by Severe Plastic Deformation

This paper investigates microstructures and mechanical properties of the TI-6AL-4V ELI alloy processed by ECAP and extrusion with various morphology of α and β-phase. Preliminary thermal treatment consisted of quenching and further high-temperature ageing. The present work reveals that the decrease of volume fraction of α-phase globular component in the initial billet results in a more homogeneous structure refinement during SPD, lower internal stress, enhancement of microstructure stability and mechanical properties. An ultimate strength of UTS ≥1350 MPa was obtained in the Ti-6Al-4V ELI alloy while maintaining a ductility of δ≥11%.

Nanostructured severe plastic deformation processed titanium for orthodontic mini-implants.

Titanium mini-implants have been successfully used as anchorage devices in Orthodontics. Commercially pure titanium (cpTi) was recently replaced by Ti-6Al-4V alloy as the mini-implant material base due to the higher strength properties of the alloy. However, the lower corrosion resistance and the lower biocompatibility have been lowering the success rate of Ti-6Al-4V mini-implants. Nanostructured titanium (nTi) is commercially pure titanium that was nanostructured by a specific technique of severe plastic deformation. It is bioinert, does not contain potentially toxic or allergic additives, and has higher specific strength properties than any other titanium applied in medical implants. The higher strength properties associated to the higher biocompatibility make nTi potentially useful for orthodontic mini-implant applications, theoretically overcoming cpTi and Ti-6Al-4V mini-implants. The purposes of the this work were to process nTi, to mechanically compare cpTi, Ti-6Al-4V, and nTi mini-implants by torque test, and to evaluate both the surface morphology and the fracture surface characteristics of them by SEM. Torque test results showed significant increase in the maximum torque resistance of nTi mini-implants when compared to cpTi mini-implants, and no statistical difference between Ti-6Al-4V and nTi mini-implants. SEM analysis demonstrated smooth surface morphology and transgranular fracture aspect for nTi mini-implants. Since nanostructured titanium mini-implants have mechanical properties comparable to titanium alloy mini-implants, and biocompatibility comparable to commercially pure titanium mini-implants, it is suggestive that nanostructured titanium can replace Ti-6Al-4V alloy as the material base for mini-implants.

Combined SPD Techniques to Fabricate Nanostructured Ti Rods for Medical Applications

The paper investigates an innovative technological processing method for fabricating nanostructured materials for structural applications. Severe plastic deformation (SPD) and subsequent thermomechanical treatment, was used to produce high physical and mechanical properties in bulk billets.

Mechanical behavior of ultrafine-grained titanium rods obtained using severe plastic deformation

We present the results of the investigation of the mechanical behavior of ultrafine-grained (UFG) titanium rods—semifinished products obtained by equal-channel angular (ECA) pressing in combination with subsequent thermomechanical treatment. This material shows ultimately high values of strength (1240 MPa) and plasticity (relative elongation 12.5%) at room temperature. At the same time, at elevated temperatures the UFG titanium exhibits signs of superplastic behavior with large relative elongations and an enhanced strain-rate sensitivity to the flow stress. The greatest elongation at fracture equal to approximately 300% was reached at 500°C and a strain rate of 10−4 s−1. The microstructure and microhardness of the samples after superplastic deformation have been investigated. It has been established that superplastic treatment can favor “structural improvement” of the UFG titanium and further enhancement in its strength.

Influence of Annealing on the Structure and Mechanical Properties of Ultrafine-Grained Alloy Ti-6Al-7Nb, Processed by Severe Plastic Deformation

This work is devoted to enhancement of strength and ductility of the Ti-6Al-7Nb ELI alloy, which is less harmful from medical point of view for human body in comparison to Ti-6Al-4V. It has been demonstrated that formation of an ultrafine-grained structure in the alloy with the help of equal-channel angular pressing in combination with heat and deformation treatments allows reaching high strength (UTS = 1400 MPa) and sufficient ductility (elongation 10 %).

Experimental study of thermodynamic and fatigue properties of submicrocrystalline titanium under high cyclic and gigacyclic fatigue regimes

This paper presents an experimental study of the mechanical and thermal behavior of titanium samples (Grade 2 and Grade 4) with different grain sizes under cyclic loading. The self-heating test demonstrates that the structure of the material has a strong effect on the dissipation ability of titanium. The threshold of energy dissipation corresponding to the transition through the fatigue limit is shown for coarse-grained titanium. On contrary, submicrocrystalline samples exhibit the dependence of continuous energy dissipation on the applied stress amplitude. Analysis of the fatigue properties of titanium in a gigacyclic regime provides evidence that grain grinding improves substantially the fatigue properties of the material.