V. V. Sagaradze

New method of mechanical alloying of ODS steels using iron oxides

Processes of mechanical alloying of oxide-dispersion-strengthened reactor pressure-vessel steels by cold high-pressure torsion of a powder mixture of low-stable Fe2O3 (Fe3O4) iron oxides and the bcc matrix alloyed with Y and Ti have been investigated using Mössbauer spectroscopy, X-ray diffraction analysis, and electron microscopy. Some features of decomposition of iron oxides and phase transformations in the matrices synthesized by mechanical alloying with formation of solid solutions supersaturated with oxygen and various compounds of oxygen with iron and alloying elements, in particular, special nanooxides of yttrium and titanium have been established.

Effect of composition and temperature on the redistribution of alloying elements in Fe-Cr-Ni alloys during cold deformation

Deformation-induced redistribution of components in a steel Kh11N30 was shown to decrease up to zero as the deformation temperature increases from 0 to 300°C. The maximum Curie temperature of deformation-induced ferromagnetic clusters formed in steels Kh11N30, Kh12N30, and Kh15N38 is the same and is equal to ∼160°C. The formation of 3–5-nm particles of an ordered L10 or L12-type phase whose amount is 5 to 10 vol % was found by field-ion microscopy.

Structure and mechanical properties of the nitrogen-containing austenitic plate steel 04Kh20N6G11AM2BF

Structure and mechanical properties of the nitrogen-containing austenitic plate steel 04Kh20N6G11AM2BF with a thickness of 20 and 40 mm after hot rolling, quenching from different temperatures, and final strengthening by cold or warm deformation have been studied. For these large-section plates, sufficiently high mechanical properties were obtained, namely, the yield stress σ0.2 ≥ 690 MPa, the relative elongation δ ≥ 20%, the relative reduction ϕ ≥ 50%, and the impact toughness KCV+20 ≥ 100 J/cm2. This complex of strength and plastic properties of hot-rolled steel was produced after the quenching of the plates from 1150°C and subsequent strengthening warm (600°C) or cold (20°C) rolling with a reduction of up to 15%. These properties of steel were due to several causes, namely, the presence of nitrogen in the fcc solid solution, an increased density of dislocations (≈ 1010 cm−2), the precipitation of nanocrystalline vanadium nitrides with sizes of 2–4 nm, and the absence of large amounts of coarse near-boundary particles.

Martensitic transformations and magnetic-field-induced strains in Ni50Mn50−x Gax alloys

Concentration dependences of the temperatures of forward and reverse martensitic transformations in Ni50Mn50−xGax alloys (x = 19–25) and features of the jumpwise elongation ε induced by magnetic field H in a single crystal of the Ni50Mn28.5Ga21.5 alloy have been studied. A single-variant state of martensite in the single crystal was formed by compression under the action of both a reference magnetic field and mechanical loading. It has been shown that when employing uniaxial mechanical compression, several large jumps (whose nature is associated with the appearance of structural defects hindering the displacement of boundaries of martensite twins) arise in curves of the single-crystal elongation induced by an applied perpendicular magnetic field H⊥.

A new approach to creation of high-strength austenitic steels with a controlled shape-memory effect

A new approach to creation of high-strength manganese austenitic steels with a controlled shape-memory effect was realized as a result of carbide dispersion hardening. The formation of VC nanocarbides differing in dispersity stabilizes or destabilizes austenite with respect to the formation of deformation-induced ɛ martensite, which makes it possible to control the magnitude of shape-memory effect and the degree of strengthening.

Structural and phase transitions in nitrided layers of iron alloys during severe cold deformation

A nanostructuring procedure similar to that proposed previously for iron alloys with carbides, nitrides (γ′-Fe4N, TiN), and oxides, was implemented for X22 fcc alloy and X18H8 austenitic stainless steel. The procedure is based on the deformation-induced dissolution of disperse CrN nitride particles in the alloy matrices and the formation of supersaturated solid solutions of nitrogen, followed by the precipitation of secondary nanonitrides inhibiting the grain growth in the matrix during heating.

Structure and thermal creep of the oxide-dispersion-strengthened EP-450 reactor steel

Production of initial and mechanically alloyed powders of oxide-dispersion-strengthened (ODS) 12Kh13M2FBR (EP-450) reactor stainless steel are considered. Structures of powders and compacted materials have been studied. The rate of thermal creep of the mechanically alloyed EP-450 ODS steel in comparison with the conventional EP-450 steel was estimated.

Radiation-induced segregation of deuterium in two-phase steel Kh16N9M3

Deuterium segregation produced in two-phase martensitic-austenitic steel Kh16N9M3 with a lath-type structure during irradiation with deuterons with an energy of 700 keV has been studied by the method of nuclear reactions. It has been shown that the intensity of the segregation and its evolution depend on the quantity and dispersion of structural constituents of the steel. It has been found that irradiation-induced austenite and deuterium-induced martensite are being formed during irradiation. The main deuterium traps in segregates are vacancy clusters and interphase boundaries.

Structure and phase composition of oxide dispersion strengthened fcc alloys prepared via strong deformation in the Fe2O3-Fe-Ni-M (M = Ti, Zr) systems

Deformation-induced Fe 2 dissolution in fcc Fe-Ni-M (M = Ti, Zr) alloys has been studied by Mössbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. The results indicate that high-pressure shear deformation in Bridgman anvil cells and ball milling lead to dissolution of the low-stability oxide Fe2O3 in the fcc matrix and the formation of metallic solid solutions and secondary oxides of the alloying elements. This enables preparation of oxide dispersion strengthened Fe-Ni alloys and grain size reduction of the fcc matrix. The formation of secondary oxides occurs more actively during ball milling than during high-pressure shear deformation because of the more significant local heating of the mixture and the larger specific surface area and higher reactivity of the powder.

Types of twins and the dislocation structure of α uranium in the initial and explosion-deformed states

Transmission electron microscopy is used to study and analyze the twin and dislocation structures of commercial-purity uranium samples in the initial (undeformed) state and after severe deformation induced by shock loading by plane waves with various intensities. As the shock loading intensity increases, the density of chaotically distributed dislocations and twins first increases, and, then, polygonization processes develop and result in a subgrain structure. Crystallographic analysis of the initial and deformation twins in uranium reveals predominant twins of the compound type {130} and rare {172} and {176} second-type twins.