Sabina Cherneva

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Verified

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• PhD
• Professor (Associate) at Bulgarian Academy of Sciences

Calcium phosphates are often used for biomedical applications. Hydroxyapatite, for example, has a wide range of applications because it mimics the mineral component of natural bone. Widespread interest in the catalytic properties of ceria is due to its use in automotive catalytic converters. Effect of electroless deposited on (non-anodized and anod...

The effect of nickel as a minority alloying element (1--3) at.% on the structure and mechanical properties of amorphous and ultrafine crystalline Al75Cu15Mg9Ni, Al75Cu15Mg8Ni2 and Al73Cu15Mg9Ni3 alloys was investigated. Rapidly solidified ribbons of the three alloys were produced by chill block melt spinning (CBMS) method. It was proven that the ra...

The mechanical properties, structure, and morphology of milled and 3D-printed Ti-6Al-4V alloys produced by selective laser melting were investigated in this study. The mechanical properties were investigated by means of nanoindentation, a tensile test, and a three-point bending test. An Atomic Force Microscope (AFM) was used to study the surface to...

Purpose: The aim of present work was to investigate microstructure and mechanical properties of 3D printed by selective laser melting (SLM) Co- Cr alloys, intended for additive manufacturing in dentistry. Methods: A scanning electron microscope (SEM), equipped with an integrated EnergyDispersive X-Ray Spectroscopy (EDS) system was used for investig...

A wide range of orthodontic archwires is used in contemporary orthodontic practice. The increasing frequency of patients with hypersensitivity to Ni, necessitates the use of Ni-free materials. Except for the composite wires, there are three metal Ni-free archwires: Titanium-Molybdenum (Ti-Mo) alloy (known by the trade names TMA™, TitanMoly™ and etc...

Effect of electroless deposited on (non-anodized and anodized) Al 1050 of: monolayer Ce2O3+Ce2O4; consecutive deposited be-layer Ce2O3+Ce2O4/Ca5(PO4)3OH or consecutive deposited be-layer Ce2O3+CeO2/(AlPO4+AlOOH+CePO4) systems on the indentation modulus (ЕIT) and hardness (HIT), as well as their corrosion-protective ability were investigated. For st...

The mechanical properties, structure, and morphology of milled and 3D printed Ti-6Al-4V alloys produced by selective laser melting were investigated in this study. The mechanical properties were investigated by means of nanoindentation, a tensile test, and a three-point bending test. The Atomic Force Microscope (AFM) was used to study the surface t...

Effect of minority alloying elements Zn and Zr on the hardness and modulus of elasticity of amorphous alloys AlCuMg(Zn) and AlCuMg(Zr) and their nanocrystalline analogues was investigated by nanoindentation. It was found that the microalloying of Al 74 Cu 16 Mg 10 with less than 1 at.% Zr increases the modulus of elasticity of the amorphous and nan...

Effect of minority alloying elements Zn and Zr on the hardness and modulus of elasticity of amorphous alloys AlCuMg(Zn) and AlCuMg(Zr) and their nanocrystalline analogues was investigated by nanoindentation. It was found that the microalloying of Al 74 Cu 16 Mg 10 with less than 1 at.% Zr increases the modulus of elasticity of the amorphous and nan...

In present work we investigated mechanical properties and phase composition of biocompatible coatings for orthopedic implants, consisting of a titanium sublayer with a developed surface morphology, on which glass-carbon coating was deposited, in order to increase its biocompatibility. The titanium sublayer with thickness 250µm was deposited using t...

The influence of the carbon introduction method on the microstructure and the mechanical properties of sinters produced from iron-based powders by diffusion-alloying sintering has been studied. Two methods of carbon introduction were tested: (1) Premixing of the base powder with graphite, and (2) Coating of the base powder with a carbon-containing...

This study aimed to characterize and compare the latest generation multi-force Bio-active™ orthodontic archwires to determine if there is a change in their physicochemical and mechanical properties during orthodontic treatment. The physicochemical characterization of the archwires was done by X-ray diffraction (XRD), scanning electron microscopy, e...

Nickel-titanium (NiTi) alloys, due to their properties of superelasticity and shape memory effect, have been extensively used in orthodontic treatment. Their superelasticity allows the orthodontist to apply an almost continuously low force with larger activation that reduces tissue trauma and patient discomfort, and thus facilitates tooth movement....

In the present work, we investigated and compared the mechanical properties of two multi-force heat-activated nickel-titanium orthodontic archwires with rectangular cross section and size 0.016 х 0.022 inches, made by two leading producers. The investigated archwires are as-received and known by the trade names Variable Force 3ТМ (Ortho Organizers...

Purpose: Most of the orthodontic archwires used in the clinical practice nowadays contain nickel (Ni), however many patients and especially kids are allergic to Ni. One possible Ni free alternative is the Titanium-Niobium (Ti-Nb) archwire. Unfortunately, there is not enough information about its mechanical properties in the literature, especially a...

Important from exploitation point of view mechanical properties of single layer, double-layer and mixed alumina and ceria films and their SS substrate were investigated by means of nanoindentation experiments. As a result we obtained the experimental load-displacement curves and calculated the indentation hardness (HIT) and indentation modulus (EIT...

The protective Zn coatings on steel substrates are preferable because the zinc layers play a role of “sacrificial coatings” due to their more negative electrode potential compared to steel substrate. Besides, their protective ability strongly depends from aggressive nature of environment, which determines the need of additional efforts. Vastly impr...

During conventional polymer injection molding, flow- and weld lines can arise at the molded parts caused by disturbed polymer melt flow when it crosses different parts of the equipment. Such processed plastic goods have discrete zones of inhomogeneities of very small dimensions. In order to stabilize the melt flow and to equalize dimensions of such...

Single thin coating of matt nickel (Nimat), a mirror bright copper (Cubright), a mirror bright nickel (Nibright) and their combinations were electrochemically deposited on brass substrate with thickness 500 μm. The basic aim was electrodeposition of two-layer Cubright/Nimat and Nibright/Cubright systems, and three-layer Nibright Cubrigh/Nimat syste...

AIM: A wide range of orthodontic archwires are used in contemporary orthodontic practice. The reports of patients with hypersensitivity to nickel (Ni) increase every year, resulting in the tendency for Ni-free materials to be used. With exception of composite wires, there are three metal Ni-free archwires: titanium molybdenum alloy (TMA), TiNb and...

Nanoindentation measurements along with atomic force microscopy, X-ray diffraction, and residual stress analyses on the basis of Raman measurements have been performed to characterize stress-tailored AlN thin films grown using reactive RF magnetron sputtering. The intrinsic stress gradient caused by the growing in-plane grain size along film thickn...

The aim of the present work is to determine the indentation hardness (HIT) and indentation modulus (EIT) of pure TiO2 and WO3 thin films, as well as thin films composed of different TiO2 and WO3 proportions and deposited by spray pyrolysis on a stainless-steel (OC 404) substrate. Since the HIT and EIT of the films are properties expected to depend...

From the point of view of the mechanics of materials, it is essential to have adequate material model for description of the elastic and plastic behaviour of metal-based thin films in order to explain the properties of coated components and construction elements. Unfortunately, the standard mechanical tests such as tensile test or pressure bulge te...

Thin Au-In alloy films containing different amounts of In were electrochemically deposited on a CuZn substrate with a 500-μm thickness. The thicknesses of the obtained films varied from 0.4 μm to 2.7 μm. The chemical and phase compositions, as well as the structures of the films, were investigated by XRF, XRD and SEM analysis. The mechanical proper...

During injection molding, flow- and weld lines can arise at the molded parts caused by disturbed polymer melt flow when it crosses different parts of the equipment: from the huge volumes in processing elements trough the sufficiently smaller gating and runner systems. Surface inhomogeneities could be most clearly seen in those areas where injection...

Mechanical properties of thin CuSn alloy films containing different content of Sn (0.06 – 67.5 wt.%) were investigated by means of nanoindentation experiments, using Nanoindenter G200 (Agilent Technologies), equipped with Berkovich indenter tip. The films were electrochemically deposited on screen-intermediate Ni film with thickness about 3 µm elec...

In living tissue, there exists a reciprocal relationship between mechanical properties and function. That is, properties affect function, and function can affect properties by means of adaptation. Thus, knowledge of mechanical properties leads directly to knowledge of function. Dynamic instrumented indentation provides a way to measure the mechanic...

Mechanical properties of three samples from liquid silicone rubber were investigated by means of microindentation experiments and finite-element simulations. The experimental and numerical load-displacement curves were compared and showed good coincidence. One of the aims of present work was seeking of correlation between some standard classical me...

The process of microindentation of nanocomposites based on epoxy resin was simulated numerically by means of finite-element method (FEM). Literature data for yield strength, tensile strength, elongation and Poisson's ratio of epoxy resin were used as initial values for numerical simulations. Numerical results obtained by means of finite-element sim...

Thin ZrO2, ZrO2–Y2O3, Al2O3 and TiO2 films were deposited by spray pyrolysis method on stainless steel OC 404 substrate with thickness 50 μm. The thicknesses of obtained films varied from 0.50 to 0.64 μm. The surface morphology and structure of the films were characterized by scanning electron microscopy in secondary electron imaging mode. The X-ra...

Recently, nanoindentation technique is gaining importance in determination of the mechanical parameters of thin films and coatings. Most commonly, the instrumented indentation data are used to obtain two material characteristics of bulk materials: indentation modulus and indentation hardness. In this paper the authors discuss the possibility by mea...

The process of microindentation of nanocomposites based on polypropylene was simulated numerically by means of finite-element method (FEM). As a result numerical load-displacement curves were obtained for a certain set of material parameters. The trial-error approach is applied to find most appropriate set which gives the best fit with the experime...

The process of microindentation of nanocomposites based on polypropylene was simulated numerically by means of finite-element method (FEM). As a result numerical load-displacement curves were obtained for a certain set of material parameters. The trial-error approach is applied to find most appropriate set which gives the best fit with the experime...

An aluminium AD-3 has been anodized under four different conditions, namely at low temperature (?5℃), room temperature (25℃), with and without sealing the anodized coating in boiling distilled water. The solution used for formation of alumina layer in all cases was an electrolyte containing 180 g/l sulphuric acid at a constant forming voltage (volt...

S. Cherneva(a), D. Stoychev(b), and R. Iankov(a) ((a)Institute of Mechanics, Bulgarian Academy of Sciences, Sofia, (b)Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria): Measuring of Mechanical Properties of Electrochemically Deposited ZrO2, Ce2O3-CeO2 and La2O3 Films by Nanoindentation Mechanical properties of ZrO2, C...

Nanomechanical testing techniques have become a common method for quantitative determination of very small volume mechanical properties. Nanoindentation testing methods are also successfully used in last years to characterize the mechanical properties of thin films. As a result of nanoindentation measurements the indentation modulus (EIT) and the i...

Cobalt layers with the thickness of 0.5 – 1,5 μm are deposited on a copper foil substrates varying the concentration of the cobalt ions (CoSO4), the reducer (NaH2PO2), as well as the pH of the electrolyte. The influence of the conditions for deposition on the morpholgy, structure, and mechanical properties (hardness, modulus of elasticity, adhesion...

In the present work, mechanical properties of electrochemically deposited thin silver layers with known thickness over brass substrates were investigated. For determination of mechanical properties of the layers, a method was used which is novel compared to those traditionally used in practice (in which, for example, a tensile test is carried out o...

A hybrid experimental-numerical approach, which combines microindentation experiments (where we measure the diagonal of the residual imprint after unloading) and numerical simulations by means of the finite-element method has been developed. The investigated materials in the present work are electrochemically deposited on brass substrates chromium...

Technology processes of thin metal films deposition are entailed with changes in material’s microstructure. As a result, deposited films often are characterized with material properties, which are different from these of the original bulk material. Determination of these material characteristics is of big importance for practice. In the present wor...

In the present work the mechanical properties of thin gold film with known thickness were investigated. The film was deposited electrochemically over brass substratum with known thickness and mechanical properties. It was realized micro indentation experiment of the film and as a result of this the experimental load-displacement curve was obtained....