Yurii Sharkeev

Microstructural features of wear-resistant titanium nitride coatings deposited by different methods☆

Titanium nitride, TiN, is used as wear protective and decorative coatings in various applications. These coatings are deposited by standard industrial methods such as chemical and physical vapor deposition (CVD and PVD, respectively), including magnetron sputtering or its modifications [e.g. the plasma-enhanced magnetron sputtered deposition (PMD) method]. The coatings have different microstructures (size and morphology of grains, orientation, dislocation structure, residual stress, etc.) depending on the method used and the deposition regime. The results of comparative transmission electron microscopy (TEM) investigations of the microstructure of thin TiN coatings deposited by classical CVD and PVD, including PMD, are presented. The microstructure was studied in sections perpendicular and parallel to the coating surface. The grain size was estimated from dark field images and the residual stress was determined using the bend extinction contours in the bright field images. It was found that the coatings deposited by PVD and CVD methods have different grain microstructures and residual stresses. The CVD coatings have an equiaxed microcrystalline structure with very low levels of the local residual stress. The mean grain size is 0.4–0.6 μm. The PVD coatings (Balzers and Metaplas) have a non-equilibrium submicron grain structure with a high level of the local residual stress equal to 0.06–0.08E, where E is Youngs modulus, and a mean grain size of 0.1–0.2 μm in the section parallel to the coating surface. The PMD coating structure is highly non-equilibrium nanocrystalline, with a very high level of residual stress equal to 0.13E and a much finer grain size of 0.06 μm.

Functional coatings formed on the titanium and magnesium alloys as implant materials by plasma electrolytic oxidation technology: fundamental principles and synthesis conditions

Abstract Metallic implants have been successfully used in medicine for the past 60–70 years. Historically, implants were designed only as mechanical devices, whereas the biological aspects of their application were beyond the researchers’ interest. The improvement of living conditions and the increase of the average life span have changed the situation. The clinical requirements for medical implants rise up substantially. Presently, it seems impossible to imagine the use of metallic implants in the human body without preliminary surface modification to modulate the interaction between the surrounding biological environment and the implant. The review highlights the most recent advances in the field of functional coatings formed on implants by the plasma electrolytic oxidation technology. Special attention is dedicated to the principles of surface modification of the commercially pure titanium, titanium nickelide, and Mg-Mn-Ce magnesium alloy. The advantages and disadvantages of the method and the characteristics of these materials are discussed from this point of view. Some aspects of this review are aimed at corrosion protection of implants with application of polymer materials.

A transmission electron microscope study of the long-range effect in titanium nitride after metal ion implantation

Abstract The improvement in the properties of tools and components after ion implantation is the result of specific structural-phase states developed both in the implanted zone (IZ) and beyond into the implantation-affected zone (IAZ). The formation of defect structures beyond the implanted zone is called the long-range effect and occurs both in metals having high plasticity and low yield strength and in high-strength materials. In the present work, the microstructure of TiN coatings deposited by PVD and CVD methods is studied by transmission electron microscopy. Before dual implantation with Ni and Ti ions the PVD coating has a highly non-equilibrium submicron crystal structure with a high level of local residual stress, whereas the CVD TiN coating has a microcrystalline structure with low internal residual stress. Implantation into PVD TiN causes a relaxation of the local stress in the IZ and beyond. In contrast, in CVD TiN ion implantation leads to the development of subgrains, both within the IZ and immediately below it, in the IAZ of the coating. No additional phases are formed in either case. A possible mechanism for explaining the formation of the defect structure beyond the IZ is introduced. This is based on the emission of a dislocation flux from stress maxima developed at the IZ–IAZ interface in the form of mezo-bands.

Structure and properties of micro-arc calcium phosphate coatings on pure titanium and Ti–40Nb alloy

Abstract The microstructure, physical and mechanical, and chemical properties of micro-arc calcium phosphate (CaP) coatings deposited under different process voltages in the range of 150–400 V on the commercially pure titanium (Ti) and Ti–40%Nb (Ti–40Nb) (mass fraction) alloy were investigated by the SEM, TEM, XRD and EDX methods. The coating thickness, roughness, and sizes of structural elements were measured and showed similar linear character depending on the process voltage for the coatings on both substrates. SEM results showed the porous morphology with spherical shape structural elements and rough surface relief of the coatings. XRD and TEM studies exhibited the amorphous structure of the CaP coating. With increasing the process voltage to 300–400 V, the crystalline phases, such as CaHPO 4 and β -Ca 2 P 2 O 7 , were formed onto the coatings. The annealing leads to the formation of complex poly-phase structure with crystalline phases: CaTi 4 (PO 4 ) 6 , β -Ca 2 P 2 O 7 , TiP 2 O 7 , TiNb(PO 4 ) 3 , TiO 2 , NbO 2 , and Nb 2 O 5 . The applied voltage and process duration in the ranges of 200–250 V and 5–10 min, respectively, revealed the coating formed on Ti and Ti–40Nb with optimal properties: thickness of 40–70 μm, porosity of 20%–25%, roughness ( R a ) of 2.5–5.0 μm, adhesion strength of 15–30 MPa, and Ca/P mole ratio of 0.5–0.7.

Modification of a disordered Ni3Fe alloy surface by 50 keV Zr ion implantation

Abstract It is well known that after ion implantation, microstructural changes are found at depths well beyond the range of the implanted ions. In the present work samples of a disordered Ni3Fe alloy, implanted with four doses of a multicomponent ion beam (where the principal component was zirconium) in the range 0.6–6.0×1017 ions cm−2, have been studied by transmission electron microscopy with subsidiary measurements being made of microhardness and residual stress in some of the samples. It is found that the implanted zone becomes increasingly amorphous and ZrO2 precipitates of increasing size appear as the implanted dose increases. These are accompanied by high internal stresses evidenced by electron micro-diffraction and confirmed by X-ray diffraction measurements. Immediately below the implanted zone, the dislocation density is increased by 2–3 times, depending on the implanted dose, and decreases monotonically down to a depth of about 10 μm. This is accompanied by corresponding increases in microhardness and residual stress which becomes increasingly tensile with the implanted dose.

High-current vacuum-arc ion and plasma source "Raduga-5" application to intermetallic phase formation

Phase composition, structural state, and mechanical properties of the ion-doped surface layers of Ni, Ti, and Fe targets with Al and Ti ions implanted into using the metal ion beam and plasma source Raduga 5 have been investigated. The high-intensity mode of implantation allowed us to obtain the ion-doped layers with the thickness exceeding the ion projected range by several orders of magnitude. By the transmission electron microscopy, it has been found that the fine-dispersed equilibrium intermetallic phases (Me3Al, MeAl) and the solid solution of aluminum were formed in the doped Ni, Ti, and Fe surface layers at the depth of up to 2600nm. The maximum dopant concentration reached 75%. It has been shown that the average size of the formed phases was of 70nm. The microhardness of the different target surface layers increased by 1.5–3 times. The wear resistance of the samples did not change within the temperature range of 300–700K.

The Biomaterial Surface Nanoscaled Electrical Potential Promotes Osteogenesis of the Stromal Cell

The calcium phosphate coating was provided onto the titanium substrate because of the nanoarc coatings technology. Both surface morphology and electrical charge of the coating were measured at the nano/micro-scaled lateral resolution. The negative electrical potential was typical for sockets, however the positive one to the peaks of the roughness. The cells were mainly attached at the negatively charged sockets. The cells expressed both osteocalcin and alkaline phosphatase that are the osteoblastic molecular markers.

Rough Titanium Oxide Coating Prepared by Micro-Arc Oxidation Causes Down-Regulation of hTERT Expression, Molecular Presentation, and Cytokine Secretion in Tumor Jurkat T Cells

The response of the human Jurkat T cell leukemia-derived cell line (Jurkat T cells) after 24 h of in vitro exposure to a titanium substrate (12 × 12 × 1 mm3) with a bilateral rough (Ra = 2.2–3.7 μm) titanium oxide coating (rTOC) applied using the micro-arc method in a 20% orthophosphoric acid solution was studied. A 1.5-fold down-regulation of hTERT mRNA expression and decreases in CD3, CD4, CD8, and CD95 presentation and IL-4 and TNFα secretion were observed. Jurkat T cell inactivation was not correlated with the generation of intracellular reactive oxygen species (ROS) and was not mediated by TiO2 nanoparticles with a diameter of 14 ± 8 nm at doses of 1 mg/L or 10 mg/L. The inhibitory effect of the rTOC (Ra = 2.2–3.7 μm) on the survival of Jurkat T cells (Spearman’s coefficient rs = −0.95; n = 9; p < 0.0001) was demonstrated by an increase in the necrotic cell count among the cell population. In turn, an elevation of the Ra index of the rTOC was accompanied by a linear increase (r = 0.6; p < 0.000001, n = 60) in the magnitude of the negative electrostatic potential of the titanium oxide surface. Thus, the roughness of the rTOC induces an electrostatic potential and decreases the viability of the immortalized Jurkat T cells through mechanisms unrelated to ROS generation. This may be useful for replacement surgery applications of rough TiO2 implants in cancer patients.

Nanoscale Electrical Potential and Roughness of a Calcium Phosphate Surface Promotes the Osteogenic Phenotype of Stromal Cells

Mesenchymal stem cells (MSCs) and osteoblasts respond to the surface electrical charge and topography of biomaterials. This work focuses on the connection between the roughness of calcium phosphate (CP) surfaces and their electrical potential (EP) at the micro- and nanoscales and the possible role of these parameters in jointly affecting human MSC osteogenic differentiation and maturation in vitro. A microarc CP coating was deposited on titanium substrates and characterized at the micro- and nanoscale. Human adult adipose-derived MSCs (hAMSCs) or prenatal stromal cells from the human lung (HLPSCs) were cultured on the CP surface to estimate MSC behavior. The roughness, nonuniform charge polarity, and EP of CP microarc coatings on a titanium substrate were shown to affect the osteogenic differentiation and maturation of hAMSCs and HLPSCs in vitro. The surface EP induced by the negative charge increased with increasing surface roughness at the microscale. The surface relief at the nanoscale had an impact on the sign of the EP. Negative electrical charges were mainly located within the micro- and nanosockets of the coating surface, whereas positive charges were detected predominantly at the nanorelief peaks. HLPSCs located in the sockets of the CP surface expressed the osteoblastic markers osteocalcin and alkaline phosphatase. The CP multilevel topography induced charge polarity and an EP and overall promoted the osteoblast phenotype of HLPSCs. The negative sign of the EP and its magnitude at the micro- and nanosockets might be sensitive factors that can trigger osteoblastic differentiation and maturation of human stromal cells.

Structure and phase composition of ultrafine-grained TiNb alloy after high-temperature annealings

The paper presents the experimental data observed in the microstructure and phase composition of ultrafine-grained Ti–40 mass % Nb (Ti40Nb) alloy after high-temperature annealings. The ultrafine-grained Ti40Nb alloy is produced by severe plastic deformation (SPD). This method includes multiple abc-pressing and multi-pass rolling followed by further pre-recrystallizing annealing which, in its turn, enhances the formation of ultrafine-grained structures with mean size of 0.28 µm involving stable β- and α-phase and metastable nanosized ω-phase in the alloy. It is shown that annealing at 500°C preserves the ultrafine-grained structure and phase composition. In cases of annealing at 800°C the ultrafine-grained state transforms into the coarse-grained state. The stable β-phase and the nanosized metastable ω-phase have been identified in the coarse-grained structure.