Yu. V. Khlebnikova

A crystallographic theory of martensitic transformations has been developed, which adequately describes their real mechanisms. A mathematical description of real processes occurring during martensitic transformation has been obtained as a product of four matrices: P₁ = R₁PB₁Г, where Г is the shear deformation of the austenite lattice, В₁ is additional “pure” deformation, the main axes of which coincide with the shear direction, with the normal to the shear plane and, accordingly, with the transverse direction, Р is the deformation of the lattice martensite with an invariant lattice, and R₁ is a slight rotation of the martensite plate to obtain an invariant plane (relaxation rotation). All four processes occur almost simultaneously, but in the specified sequence. Crystallographic analysis of eight alloys based on the theory allowed obtaining a number of important results. A relaxation rotation has been detected during martensitic transformations. A relationship has been found between the relaxation rotation and martensite texture scattering. The mechanism of packet structure formation during polymorphic transformation in a zirconium single crystal has been established. The real mechanisms of deformation during martensitic transformations in these alloys have been established.

The structure and mechanical properties of rolled sheets with a thickness of 40 mm made of lowcarbon low-alloyed steel after thermomechanical treatment of different modes are investigated. The structural factors that affect obtaining high mechanical properties are established. It is shown that a complex treatment including quenching from the rolling temperature and high-temperature tempering with a subsequent additional cycle of quenching and tempering leads to formation of rolled sheet uniform over the cross section with a fragmented bainite structure with disperse niobium carbides and carbides of cementite type. Such structure provides a yield strength of no less than 630 MPa in combination with high values of the impact energy at negative temperatures and a level of plasticity of δ ≈ 20%.

A crystallographic theory of the polymorphic bcc → hcp transition in a zirconium single crystal has been formulated. According to the theory, a mechanism of the transition includes the main parameters of the martensitic transformation, namely, the lattice strain and the strain in an invariant lattice. The package of parallel plates that are formed in the course of the transformation is considered as a single martensite crystal. It has been established that the deformation of martensite upon this transition (with an invariant lattice) is aimed at restoring the shape of the initial section of the bcc phase (prototype), rather than at obtaining an invariant plane. The calculation shows that shape restoration in the basal plane of the hcp phase is mainly caused by the action of two systems of prismatic sliding. The sliding is concentrated in narrow layers of localized shear, which leads to the formation of a lamellar structure of the package. The shape restoration along the c axis occurs due to the pyramidal sliding.

The structure and mechanical properties of rolled sheets with a thickness of 40 mm made of low-carbon low-alloyed steel after thermomechanical treatment of different modes are investigated. The structural factors that affect obtaining high mechanical properties are established. It is shown that a complex treatment including quenching from the rolling temperature and high-temperature tempering with a subsequent additional cycle of quenching and tempering leads to formation of rolled sheet uniform over the cross section with a fragmented bainite structure with disperse niobium carbides and carbides of cementite type. Such structure provides a yield strength of no less than 630 MPa in combination with high values of the impact energy at negative temperatures and a level of plasticity of δ ≈ 20%.

В настоящей работе проведен анализ кристаллографической текстуры, которая образуется в тонких эпитаксиальных лентах из медных сплавов в результате деформационного процесса и рекристаллизационного отжига при различных температурах. Определены оптимальные режимы отжига, позволяющие формировать на поверхности сплавов Cu-Ме (где Me = Ni, Fe, Cr, V) наиболее совершенную текстуру, в которой доля зерен с ориентацией {001}±10° составляет не менее 95%. Произведена оценка прочностных характеристик и коррозионной стойкости сплавов. В результате было установлено, что тонкие ленты из сплавов Cu-Ме (Me = Ni, Fe, Cr) обладающие острой биаксиальной текстурой и достаточным уровнем механических и антикоррозионных свойств могут использоваться в качестве подложек для нанесения на них функциональных...

After cold-rolling reduction with the shrinkage of more than 97 % and recrystallization annealing, the edged cubic texture develops in some fcc lattice metals with the high and medium values of stacking fault energy such as Ni, Cu, Al, Pt, and some alloys on their base. The extended bands of metals and fcc lattice alloys can be used to apply multilayer functional compositions. The authors studied the structure and crystallographic texture in bands of three-component copper-nickel-based alloys. The study showed the crucial possibility of creating multi-component alloys based on the Cu+40% Ni binary alloy doped with such elements as Mo or Nb. The paper considers the formation of an edged cubic texture in bands of Cu–Ni–Mn, Cu–Ni–Nb, and Cu–Ni–Мо alloys produced through cold deformation with rolling and recrystallization annealing performed at different temperatures. The study identified that annealing during one hour at 1050 °С was an optimal recrystallization annealing mode when on the surface of bands made of (Cu+40 % Ni)–Me alloys (where Me=Mn, Mo, Nb) deformed at ~99 %, the most perfect cubic texture was realized. According to the data obtained, after such annealing mode, from 94% to 98% of grains with orientation {001} developed in the Cu–40% Ni–1.3% Mn, Cu–40% Ni–0.8% Mo, and Cu–40% Ni–0.5% Nb alloys. It opens the prospect of using these alloys as epitaxial substrates in the technology of high-temperature second-generation superconductors. The evaluation of mechanical characteristics showed that alloying contributed to an increase in the yield strength of Cu–40% Ni–1.3% Mn, Cu–40% Ni–0.8% Mo, and Cu–40% Ni–0.5% Nb alloys by 3–4 times compared with the yield strength value of a textured copper band.

The possibility of the formation of a perfect biaxial cubic texture in ternary copper–nickel alloys with tantalum or tungsten additives was consider with the purpose to use thin rolling-strained annealed tapes as epitaxial substrates. Some experimental specimens of textured tapes were manufactured. Among recrystallization annealing variants, the optimal regime providing a perfect cubic texture with a content of twin grains of less than 3% in a tape of 100 µm in thickness was found. The substrates created from ternary copper–nickel alloys may be proposed as an alternative to the Ni–4.8 at % W alloy, which is currently applied in the technology of the production of tape substrates.

The quality of the crystallographic texture is analyzed for thin ribbons made of ternary Cu–40% Ni–Me (Me = Nb, Mo, or W) alloys, which are promising materials for epitaxial substrates. Optimal regimes of recrystallization annealing of ~100-μm-thick ribbons made of these alloys are determined, which provide perfect cubic texture with a fraction of {001}〈100〉 grains of more than 96%. The proposed alloys are paramagnetic at operating temperatures of a high-temperature superconductor and less expensive than the nickel ones; therefore, they may be an alternative to the Ni–4.8 at % W alloy, which is most popular in the production of ribbon substrates.

Specific features of structure formation at the β → α (fcc → hcp) polymorphic transformation in Co–Nb binary alloys have been investigated by metallography, scanning and transmission electron microscopies, and electron backscattering diffraction analysis. It is shown that gradual cooling of a crystallized ingot induces nucleation of α-phase crystals of several orientations (of the four ones that are possible in correspondence with the Wassermann orientation relationships) in each β grain of the alloy. Only α(hcp) martensite has been found in the structure of investigated alloys at room temperature. Misorientation of the substructure along the martensite-crystal length in the cast alloys does not exceed 1°. After homogenization and subsequent quenching in salty water, the structure of Co–Nb alloys does not undergo morphological and crystallographic changes but becomes significantly refined. In addition, misorientation of substructure elements along the martensite-crystal length increases several times, which is a consequence of the high level of quenching microstress in martensite. No phases with multilayer lattices of the NR-martensite type are revealed.