A. V. Panin

Plastic distortion as a fundamental mechanism in nonlinear mesomechanics of plastic deformation and fracture

Any deformed solid represents two self-consistent functional subsystems: a 3D crystal subsystem and a 2D planar subsystem (surface layers and all internal interfaces). In the planar subsystem, which lacks thermodynamic equilibrium and translation invariance, a primary plastic flow develops as nonlinear waves of structural transformations. At the nanoscale, such planar nonlinear transformations create lattice curvature in the 3D subsystem, resulting in bifurcational interstitial states there. The bifurcational states give rise to a fundamentally new mechanism of plastic deformation and fracture—plastic distortion—which is allowed for neither in continuum mechanics nor in fracture mechanics. The paper substantiates that plastic distortion plays a leading role in dislocation generation and glide, plasticity and superplasticity, plastic strain localization and fracture.

Fundamental role of crystal structure curvature in plasticity and strength of solids

In the paper, we use the nonlinear multiscale approach of physical mesomechanics to demonstrate that the scales of local crystal structure curvature in solids play a fundamental role in the generation of strain-induced defects and cracks. It is shown that strain-induced defects arise at the interfaces of 2D planar and 3D crystal subsystems by the mechanism of “laser pumping” and cracks nucleate as structural phase decay in the zones of crystal structure curvature where the nonequilibrium thermodynamic potential or so-called Gibbs energy is higher than zero. Nonlinear fracture mechanics eliminates the problem of singularity 1/r in equations of crack growth but requires accounting for local lattice curvature at the crack tip.

Effect of the nanostructuring of a Cu substrate on the fracture of heat-resistant Si-Al-N coatings during uniaxial tension

The effect of the nanostructuring of the surface layers in a Cu substrate on the microstructure, mechanical properties, and fracture mechanisms of heat-resistant Si-Al-N coatings during uniaxial tension is studied. The nanostructuring of a substrate is performed by the following two methods: bombardment by Zr+ ion beams and ultrasonic impact treatment. Depending on the state of the substrate, different spallation mechanisms are found to operate in the Si-Al-N coatings during mechanical loading. The maximum shear strength of the coating/substrate interface is shown to be achieved due to ion bombardment of the substrate.

On the nature of plastic strain localization in solids

Theoretical and experimental investigation is performed into the relation between plastic strain localizations of different scale in solids and the respective stress concentrators arising in the surface layer and at internal interfaces. It is found that localized plastic flow of any kind may form and propagate only under strongly nonequilibrium conditions in the zones of normal tensile stress. In the presence of excessive atomic volume, virtual nodes of a structure with higher energy emerge in the space of interstitials and a local structural transformation occurs via collective atom-vacancy configuration excitations. It is concluded that the nature of the plastic flow localization should be described on the basis of representation of strained solid as a multilevel system.

Influence of multiscale localized plastic flow on stress-strain patterns

The paper considers the influence of multiscale plastic flow localization on rotational deformation modes and σ-ɛ curves by analyzing the entropy production and equation of state of a deformed solid. It is shown that if the rotational deformation modes are fully self-consistent, the σ-ɛ curve changes monotonically. If not, the curve reveals jerks or serrations due to nonlinear wave relaxation of stresses associated with macroscale non-compensated material rotations. At high loading rates, the rotational deformation modes attain self-consistency by the mechanism of dynamic rotations.

Wrinkling of the metal–polymer bilayer: the effect of periodical distribution of stresses and strains

The viscoelastic wrinkling of aluminium films formed on silicon substrates with polystyrene interlayers (aluminium–polystyrene bilayers) is studied under thermal annealing. Compressive thermal stresses induced by the difference in thermal expansions of the bilayer and the silicon substrate are shown to lead to wrinkling instability of the Al film. The effects of annealing conditions and film thickness on the wrinkling regularities are investigated. The evolution of wrinkles, which has a three-stage character, is found to be controlled by the sign and value of in-plane stresses and those normal to the metal–polymer interface. On increasing temperature and duration of annealing, lateral extension of the aluminum–polystyrene bilayer inhibits wrinkle growth and results in smoothening of the film surface.

Structural modification of TiAlN coatings by preliminary Ti Ion bombardment of a steel substrate

The TiAlN coatings deposited onto steel 12Cr18Ni9Ti substrates before and after preliminary treatment by Ti ion beams are studied by X-ray diffraction, transmission electron microscopy, atomic force microscopy, and nanoindentation. The modification of the surface layer of a substrate is shown to change the structure and the preferred orientation of the coatings. The mechanical properties of the TiAlN coatings are found to depend substantially on the ion bombardment time.

Scale invariance of structural transformations in plastically deformed nanostructured solids

The scale-invariant mechanical behavior of a nanostructured solid is associated with plastic distortion as a major mechanism of nano- and microscale structural transformations. Active grain boundary sliding in a deformed material (microscale) within its highly developed planar subsystem (nanograin boundaries) causes a progressive increase in lattice curvature and plastic distortion of atoms which produces nonequilibrium vacant sites in the nanostructure. The motion of nonequilibrium point defects in nanostructure curvature zones provides conditions for noncrystallographic plastic flow, dissolution or dispersion of initial phases, and formation of nonequilibrium phases in a deformed material. The possibility of reversible structural phase transformations in the presence of high lattice curvature opens the way to greatly increase the fatigue life of surface nanostructured polycrystalline materials.

Effect of the number of layers in Zr-Y-O/Si-Al-N multilayer coatings on their mechanical properties and wear resistance

The peculiarities of the wear of multilayer coatings comprised of crystalline Zr-Y-O and amorphous Si-Al-N layers during tribological tests under conditions of dry friction are investigated. It is shown that the simultaneous development of the abrasive and adhesive wear mechanisms gives rise to the extreme dependence of the wear resistance of specified coatings on the number of layers. The major factors that allow one to enhance the mechanical properties and wear resistance of the investigated coatings are discussed.

Elastic stresses and microstructure of TiAlN coatings

By X-ray diffraction and transmission diffraction electron microscopy methods, the phase composition, macro- and microstresses, and microstructure in a Ti1–xAlxN coating and a substrate were investigated. The coatings were deposited by magnetron sputtering of a Ti–Al target in an Ar + N gas reaction mixture on a substrate of austenitic steel 12Kh18N10T preliminarily bombarded with a titanium ion beam. It was found that the increase in the duration of the preliminary ion treatment of the substrate leads to increasing compression macrostresses and refining of a nanocrystalline columnar microstructure in the Ti1–xAlxN coating.