L. Yu. Egorova

Mechanical properties and fracture upon static tension of the high-carbon steel with different types of pearlite structure

The hardness and mechanical properties of the U10 steel (1.03 wt % C) with pearlite structures that were formed by isothermal decomposition at temperatures of 650°C (coarse-lamellar pearlite) and 500°C (fine-lamellar pearlite) as well as upon subsequent annealing of fine-lamellar pearlite at a temperature of 650°C for 10–300 min have been studied upon tensile tests. Fractures of the steel with different types of pearlite structure have been examined using scanning electron microscopy. The interrelation between the mechanical properties and the structural features and character of fracture has been analyzed for this steel with pearlite structures differing in the dispersity, morphology, and defect structure of cementite, and in the levels of solid-solution strengthening and microdistortions of the ferrite-constituent lattice.

Perfect cubic texture, structure, and mechanical properties of nonmagnetic copper-based alloy ribbon substrates

A sharp cubic texture is formed in a number of copper alloys subjected to cold deformation by rolling by 98.6–99% followed by recrystallization annealing, which opens up fresh opportunities for long thin ribbons made of these alloys to be used as substrates in the production of second-generation high-Tc superconductor (2G HTSC) cables. The possibility of creating ternary alloys based on a binary Cu-30 at % Ni alloy with additional elements that harden its fcc matrix (iron, chromium) is shown. The measurements of the mechanical properties of textured ribbons made of these alloys demonstrate that their yield strength is higher than that of a textured ribbon made of pure copper by a factor of 2.5–4.5.

Structural features of the behavior of a high-carbon pearlitic steel upon cyclic loading

The structural evolution upon high-cycle fatigue (tension with the magnitude of stress in a cycle below the macroscopic yield stress) of the hypereutectoid steel U10 (1.03 wt % C), in which pearlite of different morphology (fine-lamellar, coarse-lamellar, and partially spheroidized pearlite) was formed, has been investigated by scanning and transmission electron microscopy. Based on the fractographic analysis, features of fracture of these structural states have been considered. At a significant distance (10 mm) from the fatigue fracture, features of structural transformations caused by cyclic loading have been revealed. It has been shown that upon high-cycle fatigue in the steel U10 with structures of lamellar and partially spheroidized pearlite, substantial structural changes occur, namely, fragmentation and partial dissolution of cementite plates, and in fine pearlite, additionally, spheroidizing of cementite and polygonization of the ferritic component are observed. A dependence of the character of fracture on the type of structure formed upon fatigue loading has been established. In the steel with a nonequilibrium structure of unannealed fine pearlite, an enhanced elasticity modulus, as compared to other more stable structures (coarse-lamellar, annealed fine, and spheroidized pearlite), and a reduction in the magnitude of the elasticity modulus under the action of cyclic loading have been found. It has been established that the structural changes in fine pearlite of laboratory specimens of the steel U10 upon cyclic tension are qualitatively similar to those in a railroad wheel of the steel 65G under the service conditions.

Creating textured substrate tapes of Cu-Fe alloys for second-generation high-temperature superconductors

It is established that Cu-1.6 at % Fe alloy tapes obtained through cold rolling to 98.9% followed by recrystallization annealing possess a sharp cube texture, which opens prospects of using thin tapes of this alloy as substrates for second-generation high-temperature superconductors. The optimum regime of annealing is determined that allows an alloy with sharp biaxial texture containing more than 97% cubic grains to be obtained. The yield stress of a 90-μm-thick Cu-1.6 at % Fe alloy tape upon recrystallization annealing at 800°C for 1 h amounts to 78 MPa, which is about three times higher than the value for a pure copper tape with sharp cube texture.

Evolution of the structure of an α-titanium single crystal during high-pressure torsion

The microstructure of an iodide titanium single crystal subjected to severe plastic deformation in Bridgman anvils at a pressure of 8 GPa and room temperature or the liquid-nitrogen temperature is studied by electron microscopy and X-ray diffraction. The initial α-titanium single crystal undergoes the baric α→ω transformation during compression and deformation under pressure. A decrease in the deformation temperature to 80 K is found to activate twinning. Upon deformation up to a strain e = 6, the strain hardening at room temperature exceeds the low-temperature strain hardening. At higher strains, the room-temperature strain hardening begins to decrease as compared to the low-temperature strain hardening due to the development of dynamic and postdynamic recrystallization. A decrease in the deformation temperature to 80 K suppresses recrystallization; correspondingly, titanium deformed in liquid nitrogen exhibits a larger microhardness increment in the strain range 6 < e < 10.

Features of forming structure of titanium pseudosingle crystal during β → α (bcc → hcp) polymorphic transformation

The structure of a titanium iodide single crystal obtained by zone melting has been studied by metallography, X-ray diffraction, and electron microscopy. It has been shown that the initial bcc titanium single crystal becomes a pseudosingle crystal upon cooling below the temperature of the β → α polymorphic transition. The pseudosingle crystal consists of macroscopic packets, i.e., crystals of lath morphology with a size of 0.1–0.5 cm2 in different crystal sections. Each packet consists of α-phase laths of the same orientation, which are separated by dislocation boundaries. A total of six different types of packets in the pseudosingle crystal volume is realized in accordance with the Burgers orientation relationships. The structural heredity in the titanium pseudosingle crystal after the cycle of the α → β → α transformations is confirmed.

Wear Resistance of Carbon Steel with a Structure of Thin-Plate Pearlite

The effect of annealing performed at a temperature below point A1 on the wear resistance and microhardness of carbon steel with an original structure of thin-plate pearlite is investigated. It is shown that such a structure possesses a high wear resistance that decreases even after a short-term annealing that has not yet caused spheroidization of cementite and polygonization of ferrite. Specimens with a structure of freshly formed thin-plate pearlite are shown to have a high hardness in the original state but harden under the action of friction more intensely than specimens with other kinds of structure.

Cubic texture of recrystallization of ribbon substrates made of nickel alloys alloyed with W, Mo, and Re refractory elements

The processes of the formation of deformation and recrystallization textures in nickel alloys containing W, Mo, and Re are studied. The problems of optimizing the annealing regimes for recrystallization are considered taking into account the increase in the starting temperature of primary recrystallization in nickel alloys that contain refractory metals after rolling to large strains. The mechanical and magnetic properties of all the alloys are analyzed. The tendency of Ni95.3Mo4.7, Ni95.2W4.8, Ni95.9Re4.1, and Ni95.2Re4.8 to oxidize is studied by the thermogravimetry technique. It has been found that, of all the studied alloys, the Ni95.3Mo4.7 alloy has the best corrosion-resistant properties at high temperatures (600–700°C) and the lowest specific magnetization at working temperatures of a high-temperature superconductor.

Behavior of pearlite of various morphologies during cyclic tension

The structural evolution of hypereutectoid U10 steel with a pearlitic structure of various types (fine lamellar or partly spheroidized pearlite) is studied during fatigue loading. The fracture of these structures is considered using fractography data. The specific features of the structural transformations and the changes in the dislocation structure of the U10 steel are revealed during cyclic tension in the high-cycle fatigue region at a significant distance (10 mm) from a fatigue fracture surface. Substantial structural changes are shown to occur in U10 steel with various pearlitic structures during high-cycle fatigue tests (tension at a stress amplitude in a cycle lower than the macroscopic yield strength). These are the fragmentation, partial dissolution, and spheroidization of cementite lamellae and the polygonization of the ferrite component. The relationship between the type of fracture surface and the type of structure formed upon fatigue loading is found.

Effect of thermomechanical treatment on the cold resistance of low-carbon low-alloy welding steel

Effect of the structure and texture formed upon thermomechanical treatment (TMechT) on the cold resistance of low-carbon low-alloy welding steel is considered. The structure has been investigated by the metallographic and electron-microscopic methods; the texture has been studied by X-ray diffraction method with the aid of the analysis of the orientation distribution function (ODF). Structural factors that affect an increase in the cold resistance, including creation of a submicrocrystalline structure, have been considered. It has been established that the components of the texture result from a regular crystallographic rearrangement of the texture of hot deformation of austenite into the texture of the α phase upon the γ → α transformation. It is shown that the dependence of the cold resistance of the rolled sheet on the fraction of the cube component in the texture of the α phase has a complex nonmonotonic nature.