V. P. Pilyugin

Nanostructurization of Nb by high-pressure torsion in liquid nitrogen and the thermal stability of the structure obtained

The evolution of the Nb structure upon high-pressure torsion (HPT) in a Bridgeman chamber in liquid nitrogen and a subsequent annealing in the range from 100 to 600°C has been studied by the TEM method. With an increase in the degree of deformation, the structure exhibits three stages of refinement: dislocation cellular structure; mixed structure consisting of cells and subgrains; and submicron or nanocrystalline grain structure. The HPT using 3 and more revolutions of the anvils at 80 K leads to the formation in Nb of a nanocrystalline structure with an average grain size of ∼75 nm and a record high microhardness of 4800 MPa. The structure is stable at room temperature but possesses a relatively low thermal stability, i.e., the recrystallization starts at lower temperatures than it does after conventional deformation or an HPT at room temperature.

Structure evolution of pure iron upon low-temperature deformation under high pressure

Structure evolution of iron (99.97% purity) deformed by shear under pressure at 80 K in a medium of liquid nitrogen has been investigated. It has been found that, along with dislocation slip, twinning and development of deformation microbands become operative mechanisms of low-temperature deformation. This led to specific type of inhomogeneity of the structure in which, up to ultimately attained degrees of deformation, low-angle misorientations are retained and, unlike room-temperature deformation, no homogeneous submicrocrystalline (SMC) structure is formed. Twinning contributes to the refinement of structure elements that are more than 1 μm in size; the further refinement occurs by the dislocation-disclination mechanism and goes to the steady-state stage.

Structure and Thermal Stability of Cu after Severe Plastic Deformation

Evolution of structure of high-purity and commercially pure copper at severe plastic deformation (SPD) by high pressure torsion (HPT) at room temperature and in liquid nitrogen has been studied by transmission electron microscopy (TEM) and measurements of microhardness. Thermal stability of structure obtained by HPT has been investigated. Factors preventing from obtaining nanocrystalline structure in Cu are analyzed and possible ways of their overcoming are discussed.

Thermal stability of nickel structure obtained by high-pressure torsion in liquid nitrogen

Using transmission electron microscopy and durometry, the structural evolution of commercially pure nickel (99.6%) under high-pressure torsion (HPT) in liquid nitrogen and subsequent annealings in the temperature range 100–400°C has been investigated. In this nickel, at cryogenic temperature, HPT gives rise to a nanocrystalline structure with the record high microhardness (6200 MPa) and average crystallite size ∼80 nm. The obtained structure is stable at room temperature and possesses a relatively low thermal stability, since recrystallization occurs at lower temperatures than after conventional deformation or HPT at room temperature.

Evolution of the structure of V95 aluminum alloy upon high-pressure torsion

The effect of the degree of deformation upon torsion under quasi-hydrostatic pressure on the structural and phase transformations in the V95 alloy has been studied by the methods of electron microscopy and X-ray diffraction. It has been found that, upon severe plastic deformation, a nanocrystalline structure with a hardness of 2.5 GPa is formed. The nanostructure with a minimum average grain size of 55–80 nm is being formed at e = 5.5–6.4. It has been shown that during dynamical strain aging at e ≥ 4.8, a hardening metastable phase MgZn2 precipitates from the supersaturated α solid solution, and the quantity of this phase increases with increasing degree of deformation.

Structure and mechanical properties of aging Al-Li-Cu-Zr-Sc-Ag alloy after severe plastic deformation by high-pressure torsion

The structural and phase transformations have been studied in aging commercial aluminum-lithium alloy Al-1.2 Li-3.2 Cu-0.09 Zr-0.11 Sc-0.4 Ag-0.3 Mg in the as-delivered state and after severe plastic deformation by torsion for 1, 5 and 10 revolutions under a high pressure of 4 GPa. Deformation-induced nanofragmentation and dynamic recrystallization have been found to occur in the alloy. The degree of recrystallization increases with deformation. Nanofragmentation and recrystallization processes are accompanied by the deformation-induced decomposition of solid solution and changes in both the nucleation mechanism of precipitation and the phase composition of the alloy. The influence of a nanostructured nanophase state of the alloy on its mechanical properties (microhardness, plasticity, elastic modulus, and stiffness) is discussed.

Phase and structural transformations in the aluminum amts alloy upon severe plastic deformation using various techniques

The paper presents experimental data on the structure formation in the commercial aluminum alloy of grade AMts subjected to severe plastic deformation using dynamic channel-angular pressing and torsion under high quasi-hydrodynamic pressure in Bridgman anvils. The dependences of the structural characteristics and hardness on the degree, rate, and scheme of deformation have been analyzed.

Effect of severe plastic deformation on the formation of the nanocrystalline structure and the aging of the multicomponent aluminum-lithium alloy with small additions of Sc and Mg

Effect of severe plastic deformation and subsequent low-temperature annealing on the structural and phase transformations, which are realized in the alloy 1450 on the base of the Al-Li-Cu-Zr system with additives of Sc and Mg has been studied by electron microscopy. The possibility of obtaining a nanocrystalline recrystallized structure in the alloy investigated has been established. It has been shown that its uniformity and dispersiveness depend on the degree of deformation and on the regime of annealing and are determined by the density distribution of particles that are precipitated upon the decomposition of the supersaturated solid solution. The transition of the alloy from microcrystalline to submicrocrystalline or nanocrystalline state changes its phase composition, morphology, and mechanism of nucleation of the precipitated phases and makes it possible to minimize structural factors that exert negative effect on the alloy plasticity.

Structure, thermal stability, and state of grain boundaries of copper subjected to high-pressure torsion at cryogenic temperatures

Evolution of the structure of tough-pitch copper upon severe deformation by high-pressure torsion at room temperature and in liquid nitrogen is studied. The thermal stabilities of the resulting structures are investigated. The state of grain boundaries is examined by means of Mössbauer emission spectroscopy. Factors that hamper the formation of a nanostructured state and the possibility of eliminating the effect of these factors are analyzed.

Effect of storage on the stability of the grained structure and phase transformations in the nanocrystalline alloy 1450 doped with Sc and Mg

The effect of long-term storage on the structural and phase transformations in the alloy 1450 doped with Sc and Mg additions based on the Al-Li-Cu-Zr system has been investigated after severe plastic deformation by torsion under pressure and subsequent low-temperature annealing using electron microscopy and X-ray diffraction analysis. It has been found that in the strongly deformed alloy, upon storage, there simultaneously occur a recrystallization accompanied by a transformation of the alloy structural constituents and a decomposition of the supersaturated solid solution. Annealing of the deformed alloy yields a stable nanocrystalline structure.