V. V. Korenkov

Size effects in the hardness of fcc metals on micro- and nanoscales

The size effects in the hardness of three fcc metals, namely, Ni, Cu, and Al, are studied by micro- and nanoindentation, and the boundaries of regions with size effects of various types and the characters of these effects are determined.

Determination of the time-dependent plastic properties of solids by dynamic nanoindentation

A new method is described to determine the time-dependent elastoplastic and dissipative properties of solids in nanovolumes by recording the instantaneous values of the stress and depth of penetration of a rigid indenter. Measurements are also made of the energy W1 supplied to the indenter, the energy U dissipated in the insertion process, and the energy W0 returned to the indenter on unloading. Results of measurements of the dynamic microhardness and also of the energies W0 and U for NaCl crystals are presented as functions of the duration of contact between the indenter and the surface for times between 1 ms and 10 s.

Improvement in the nanoindentation technique for investigation of the time-dependent material properties

Abstract An improved nanoindentation technique was developed for dynamic investigation of the time-dependent properties of materials under conditions close to real nanocontact interaction during dry friction, abrasive wear, milling, mechanical alloying and so on. For these purposes the duration of the loading- unloading cycle was reduced to 20ms and a nanocontact fatigue test was performed with the number of reloading cycles reaching 103-105.

The effect of small-amplitude load oscillations on the nanocontact characteristics of materials in nanoindentation

A continuous stiffness measurement method allowing one to obtain physical-mechamical characteristics of materials in the process of indentation during gradually increasing loading has been scrutinized. The limits of applicability of this approach depend on the testing conditions at which the additional smallamplitude oscillations exert no influence on the mechanics, kinetics, and plastic strain of material being in contact with the indenter. As is shown by taking as examples specimens with amorphous structure, and fcc and bcc lattices, various techniques for determining the nanocontact characteristics of materials are different by their sensitivity to small-amplitude load oscillations. The oscillation amplitudes and the indentation depth ranges where one can neglect the oscillation effects have been evaluated. The impacts of the oscillations on the behavior of the contact (local) characteristics of the studied materials in supercritical modes have been established.

Dynamic characteristics of solids in microvolumes: Modern principles, techniques, and results of investigation

Several radically new independent in situ techniques for characterizing physicomechanical properties of materials in microvolumes are described. In particular, mechanisms behind the formation of an indent and the surrounding deformation zone were studied at a microlevel. With ionic crystals, it was demonstrated that indentation, followed by the formation of the deformation zone, passes the following stages: purely elastic deformation stage, the stage of monoatomic displacement of a material from under the indenter; and a number of final stages where dislocation plasticity is essential. Kinetic, dissipative, and activation parameters of indentation were determined, and basic mass transfer micromechanisms for each of the stages were elucidated.

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.

Nanomechanical testing of ODS steels irradiated with 1 MeV/amu heavy ions

Abstract Development of oxide dispersion strengthened (ODS) steels, as candidates for fuel claddings for Gen IV nuclear reactors, requires a comprehensive study of their behaviour under operating conditions. In this work, 1.2 MeV/amu Kr and Xe irradiation was used to simulate fission fragment impact. New irradiation approaches with respect to a non-homogeneous damage profile under ion irradiation were proposed. Hardness profiles of irradiated ODS steels were obtained by continuous stiffness measurements with subsequent analysis of size effects according to the Nix–Gao model. It was found, that heavy ion irradiation leads to hardness saturation in ODS steels in a damage dose range of 0.1–1 dpa. Observed hardening is about 20% and is not connected with the radiation stability of Y–Ti–O and Y–Al–O oxide particles in ODS steels as it was studied by TEM.