V. I. Ivolgin

Serrated plastic flow during nanoindentation of a bulk metallic glass

The results of nanoindentation tests of bulk glassy Pd40Cu30Ni10P20 using a specially designed instrument with high time and spatial resolution are presented. Pronounced serrations of the indenter penetration depth are observed. The parameters of serrated flow (the number of serrations, their amplitude and duration) are dependent on the duration of the loading force pulse.

Kinetic features of the deformation of solids in nano-and microscopic volumes

The deformation dynamics of nanovolumes in crystalline, quasicrystalline, and amorphous solids is studied experimentally using continuous nanoindentation with a resolution of 0.1 nm. The elastic limits of some materials are determined in a nanocontact region. A jumplike transition to a plastic flow (which is equivalent to a drop in yield in uniaxial macroscopic tests) is revealed and studied. The dynamics and statistics of an unstable plastic flow in strain-aging alloys are analyzed. The specific features of a local stress-strain curve associated with a phase transformation under an indenter and with microcrack nucleation are revealed. The load-carrying ability of a material upon nanocontact loading is shown to be many times its macroscopic yield strength and to approach the theoretical ultimate strength even in plastic materials. The relaxation processes occurring in submicrovolumes after unloading are found to induce an elastic aftereffect that is much larger than that in macroscopic tests. In Si and Ge single crystals, the effect of a jumplike increase in the cracking resistance with the strain rate is detected.

Serrated deformation of a Pd40Cu30Ni10P20 bulk amorphous alloy during nanoindentation

Depth-sensing (indentation) testing is used to study the characteristics of a serrated plastic flow in a Pd40Cu30Ni10P20 bulk amorphous alloy, and the boundaries between the regions of serrated and homogeneous plastic deformation are determined.

Unstable Plastic Flow in the Al-3% Mg Alloy in the Process of Continuous Nanoindentation

Methods of dynamic nanoindentation were used to study unstable modes of plastic flow in micro-and submicrovolumes of the Al-3% Mg alloy. It was established that, depending on the rate of loading and dimensions of the deformed region, various regimes of unstable plastic deformation are realized. In the course of deformation, the irregular deformation curve (corresponding to a random process) reveals a quasi-periodic behavior with a characteristic amplitude of hardness oscillations.

Regions of the portevin-Le chatelier effect existing under the conditions of continuous room-temperature indentation of an Al-2.7% Mg alloy

Dynamic indentation is used to study the character of a plastic flow during room-temperature deformation of an Al-2.7% Mg alloy in micro-and submicrovolumes (the indentation depth is varied from 50 nm to 15 µm) at strain rates varying in the range 0.0005–1 s−1. In this region of parameters, the boundaries of stable deformation and two modes of unstable deformation have been found.

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.

Investigation of the effect of electric current on serrated deformation and acoustic emission in the aluminum-magnesium alloy 5056

The effect of direct electric current on the serrated deformation of the aluminum-magnesium alloy 5056 has been studied using the acoustic emission method and high-speed video filming of propagating deformation bands. The phenomenon of the electric current-induced suppression of low-frequency acoustic emission signals has been revealed in the range of 1 Hz–2 kHz, which is connected with the development of Portevin-Le Chatelier deformation bands. The characteristic times of damping and growth of plastic instabilities and acoustic signals caused by them after current turn-on and turn-off, respectively, have been estimated.

Monotonic and jumpwise deformation of bulk amorphous Zr46.8Ti8Cu7.5Ni10Be27.5 alloy in nanoindentation

AbstractThe study is aimed at the establishment of regions of stable (monotonic) and unstable (jumpwise) plastic flow in bulk amorphous Zr46.8Ti8Cu7.5Ni10Be27.5 alloy under the conditions of local deformation. The characteristics of the jumpwise plastic flow in bulk amorphous Zr46.8Ti8Cu7.5Ni10Be27.5 alloy are studied by the method of continuous nanoindentation (depth-sensing testing) in the range of strain rates

Size effect and time-dependent nanohardness of ZrO2-based ceramics

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