T. S. Pirozhkova

Enhancement of the mechanical properties of AZ31 magnesium alloy via nanostructured hydroxyapatite thin films fabricated via radio-frequency magnetron sputtering

The structure, composition and morphology of a radio-frequency (RF) magnetron sputter-deposited dense nano-hydroxyapatite (HA) coating that was deposited on the surface of an AZ31 magnesium alloy were characterized using AFM, SEM, EDX and XRD. The results obtained from SEM and XRD experiments revealed that the bias applied during the deposition of the HA coating resulted in a decrease in the grain and crystallite size of the film having a crucial role in enhancing the mechanical properties of the fabricated biocomposites. A maximum hardness of 9.04 GPa was found for the HA coating, which was prepared using a bias of -50 V. The hardness of the HA film deposited on the grounded substrate (GS) was found to be 4.9 GPa. The elastic strain to failure (H/E) and the plastic deformation resistance (H(3)/E(2)) for an indentation depth of 50 nm for the HA coating fabricated at a bias of -50 V was found to increase by ~30% and ~74%, respectively, compared with the coating deposited at the GS holder. The nanoindentation tests demonstrated that all of the HA coatings increased the surface hardness on both the microscale and the nanoscale. Therefore, the results revealed that the films deposited on the surface of the AZ31 magnesium alloy at a negative substrate bias can significantly enhance the wear resistance of this resorbable alloy.

The physical and mechanical properties and local deformation micromechanisms in materials with different dependence of hardness on the depth of print

The size hardness effects are studied via the micro- and nanoindentation methods over the wide range of the depth of print h (from dozens of nanometers to several dozen micrometers) for several classes of materials, such as ionic and covalent single crystals (sapphire, silicon, lithium fluoride); metals (single-crystal Al, polycrystalline Cu, Ni, and Nb); ceramics (high-strength nanostructured TZP-ceramic based on the natural zirconium dioxide–baddeleyite mineral); amorphous materials (fused quartz); and polymers (polycarbonate and polytetrafluoroethylene). As is shown, some of them possess severe size hardness effects, whereas the others reveal the weak ones or even a lack of these effects. The thermoactivation analysis is implemented, as well, and the activating and energy characteristics of local deformation processes induced by an indenter are compared with the dominant plasticity micromechanisms of the studied materials at different stages of the print formation and with the size peculiarities. The materials with low hardness coefficients and meeting the requirements of ISО 14577 and GOST R 8.748-2011 standards in the nanohardness measurements are highlighted, as well. In the established load ranges, these materials are the promising candidates for their use as reference samples, which are designed to ensure the uniformity of the hardness measurements at the nano- and microscales, as well as for calibrating and testing the nanoindentometers.

Physico-mechanical properties and micromechanisms of local deformation in thin near-surface layers of complex multiphase materials

Size effects in the local mechanical properties of multiphase materials are studied by means of micro- and nanoindentation. The numerical values of the elasticity modulus, hardness, and crack resistance of single phases and interphase boundaries in several rock samples (polycrystalline banded iron formations, granite, anthracite, sandstone, marble, and serpentine marble) are determined. The strongest and weakest intergrowth boundaries in the investigated materials are established. Thermal activation analysis is performed, and the activation and energy characteristics of local deformation in a material under an indenter are identified. The predominant micromechanisms of plasticity in single phases and inclusions in rocks under the action of high local stresses are identified.

Nanoindentation of a hard ceramic coating formed on a soft substrate

The hardness and Young’s modulus of the thin hydroxyapatite-based coatings deposited by RF magnetron sputtering onto magnesium alloy, titanium, and steel substrates are studied. As the penetration depth increases, the hardness and Young’s modulus of these coatings are found to tend toward the values that are characteristic of the substrates. It is shown that the difference between the values of hardness and Young’s modulus at small penetration depths (h < 80–100 nm) can be caused by the difference between the physicomechanical properties inside the coatings and that this difference at large penetration depths (h > 100 nm) can be induced by an additional effect of the strength properties of the substrate material.

Size Effects and Charting the Physical and Mechanical Properties of Individual Phases and Interphases in Polycrystalline Materials

Size effects in the hardness of individual phases and inclusions of multiphase materials are studied via micro- and nanoindentation for a number of rock samples (polycrystalline ferruginous quartzites, granite, anthracite, sandstone, marble, and verd antique). The distribution of the local physical and mechanical properties of the studied materials is charted. Size effects in hardness and correlations between the distribution of local physical and mechanical properties and the morphology of the studied samples are found.

New nanostructured ceramics from baddeleyite with improved mechanical properties for biomedical applications

A method for the preparation of novel nanostructured zirconia ceramics from natural zirconia mineral—baddeleyite—using CaO as the stabilizer is described in the present work. Optimal synthesis conditions, including calcia content, planetary mill treatment regime, sintering time and temperature, corresponding to the highest values of hardness H, Young modulus E, and fracture toughness KC are found. The values of the mechanical properties H = 10.8 GPa, E = 200 GPa, and KC = 13.3 MPa m1/2 are comparable with or exceed the corresponding properties of commercial yttria-stabilized ceramics prepared from chemically precipitated zirconia.

Improvement of the Mechanical Properties of AZ91D Magnesium Alloys by Deposition of Thin Hydroxyapatite Film

Structural and mechanical behavior of thin hydroxyapatite (HA) films deposited via radio-frequency magnetron sputtering on AZ91D magnesium alloy was investigated. Nanoindentationwas employed to evaluate nanohardness and Young’s modulus of the uncoated and HA-coated AZ91 magnesium alloy. The HA-coated AZ91D magnesium alloy exhibited a higher hardness of 7.1 GPa and a higher modulus of 86 GPa compared withthe uncoated substrate revealing a strong load-bearing capacity.

Novel Baddeleyite-Based Zirconia Ceramics for Biomedical Applications

For the first time nanostructured engineering ceramics were prepared from natural zirconia mineral (baddeleyite) with CaO as a tetragonal phase stabilizer. The effect of synthesis conditions on microstructure and mechanical properties of the baddeleyite-based ceramics is reported, furthermore, the effect of calcia content on hardness and fracture toughness is studied. Optimal calcia concentration and synthesis conditions are found, corresponding hardness and fracture toughness values are 10,8 GPa and 13,3 MPa×m1/2. The reported mechanical properties are comparable to those typically reported for yttria-stabilized engineering zirconia ceramics, prepared from chemically synthesized zirconia.

Size effects of the strength and elastic properties of individual phases and interphase boundaries of polycrystalline materials

Size effects of hardness are studied and numeric values of Young’s modulus E, hardness H, and fracture toughness coefficient Kc of individual phases and interphase boundaries of polycrystalline samples of ferruginous quartzite are determined by means of micro- and nanoindentation methods. It is found that the interphase boundary of magnetite and hematite is the one most strengthened, while the boundary of the hematite and quartz is the one least durable.

Methods of micro- and nanoindentation for characterization of local physical and mechanical properties of multiphase materials

Processes of local deformation and fracture of the surface of a number of rocks (ferruginous quartzite, granite, marble, serpentine, anthracite, sandstone) are studied by means of micro- and nanoindentation under high local loadings. Numerical values of elastic, plastic and strength (hardness, Young’s modulus, fracture toughness, etc.) properties of rock specimens are defined in a wide range of loads and indentation depth h (from 10 nm to 50 µm). The influence of size effects on hardness is studied, including in other physical and mechanical properties of individual phases and interphase boundaries of a wide range of rocks. Moreover, nonmonotonic dependences of hardness of certain mineral components of studied rock specimens are identified on the micro- and nanoscale. It is found that the hardness of individual mineral phases naturally increases with decreasing indentation depth up to 60–120 nm depending on the type of a rock specimen and the phase type, and then begins falling. Values of the coefficient ...