N. F. Vil’danova

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 severe plastic deformation on the microstructure and tribological properties of a babbit B83

The effect of severe plastic deformation carried out at room temperature by the methods of equal-channel angular (ECA) pressing and surface friction treatment (SFT) on the microstructure, rate of wear, and friction coefficient of a babbit B83 (11.5% Sb, 5.5% Cu, Sn for balance) has been investigated. It has been shown that severe plastic deformation that leads to a drop in the grain size of the babbit to 100–300 nm and to a strong refinement of particles of intermetallic phases (SnSb, Cu3Sn) causes a considerable (twofold-fourfold) reduction in the rate of wear and a decrease in the friction coefficient of a steel-babbit pair under test conditions with lubrication at small (0.07 m/s) and enhanced (4.5 m/s) sliding velocities. As was shown by structural investigations performed with the use of scanning electron microscopy, this positive influence of severe plastic deformation on the tribological properties of the babbit is connected with the formation on the deformed-babbit surface of a developed porosity, which improves conditions for lubrication of the babbit-steel friction pair due to the action of the self-lubrication effect and thereby favors the retention of a stable regime of boundary friction of this pair. The formation of porosity is a result of the accelerated spalling of hard brittle intermetallic particles of SnSb and Cu3Sn from the friction surface of the deformed babbit, which is caused by weakening and loss of the bonding of these particles with the plastic matrix (α solid solution based on tin) in the course of severe plastic deformation of the babbit. At the same time, under the conditions of dry sliding friction of the babbit-steel 45 pair, when a fatigue mechanism of wear of the alloy under consideration predominantly develops, this plastic deformation yields an approximately 1.6-fold increase in the rate of wear of the babbit. This increase is mainly due to numerous defects (microcracks) that are introduced into the babbit structure upon its severe plastic deformation and reduce the resistance of the surface layer of this material to the fatigue mechanism of wear.

Preparation, deformation, and failure of functional Al-Sn and Al-Sn-Pb nanocrystalline alloys

Changes in the structure, hardness, mechanical properties, and friction coefficient of Al-30% Sn, Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb (wt %) alloys subjected to severe plastic deformation by equal-channel angular pressing (with a force of 40 tonne) and by shear at a pressure of 5 GPa have been studied. The transition into the nanocrystalline state was shown to occur at different degrees of plastic deformation. The hardness exhibits nonmonotonic variations, namely, first it increases and subsequently decreases. The friction coefficient of the Al-30% Sn, Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb alloys quenched from the melt was found to be 0.33; the friction coefficients of these alloys in the submicrocrystalline state (after equal-channel angular pressing) equal 0.24, 0.32, and 0.35, respectively. The effect of disintegration into nano-sized powders was found to occur in the Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb alloys after severe plastic deformation to ɛ = 6.4 and subsequent short-time holding.

Nanostructure Formation and Phase Transformations in Nitrided Stainless Steel Kh18N8 during Severe Cold Deformation

The phase transformations and nanostructure formation in metastable stainless steel Kh18N8 are studied during nitriding and subsequent severe cold plastic deformation by high-pressure torsion in Bridgman anvils. Ion-plasma nitriding of the steel leads to the nitrogen saturation of austenite, CrN nitride formation, and the destabilization of the structure with respect to the γ-α transformation. Subsequent deformation is accompanied by the reverse α-γ phase transformation, the dissolution of nitrides, and the formation of nitrogen-supersaturated solid solutions and secondary nanonitrides. These fine particles restrict the grain growth in the matrix and stabilize the nanostructure formed.

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.

Deformation-induced cyclic phase transitions of dissolution-precipitation of nitrides in surface layers of Fe-Cr-(Ni)-N alloys

Methods of Mössbauer spectroscopy, transmission electron microscopy, and X-ray diffraction have been used to study structural and phase transformations in surface layers of iron and Fe-Cr-(Ni) alloys subjected to ion-plasma nitriding and subsequent severe cold plastic deformation by shear under pressure in Bridgman anvils. It has been shown that the cyclic phase transformations of dissolution-precipitation of nitrides in the alloys result in the formation of nitrogen-supersaturated solid solutions, precipitation of secondary nitrides, and the nanostructurization of the metallic matrix. It has been established that the introduction of chromium into iron alloys accelerates the formation of nitrides upon nitriding and makes it possible to obtain solid solutions strongly supersaturated with nitrogen (more than 10 at % N in the fcc lattice) during subsequent deformation.

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.

Dissolution of the Fe4N nitride in the nitrided layer of iron upon cold deformation by shear under pressure

Mössbauer spectroscopy, X-ray diffraction, and transmission electron microscopy were used to study structural and phase transformations upon cold (300 K) deformation by shear under pressure in thin layers of nitrides Fe4N formed on the surface of bcc iron. Strain-induced dissolution of nitrides in bcc iron with the formation of bcc and fcc solid solutions supersaturated with nitrogen and secondary Fe16N2 and Fe4N nitrides was found. The dispersiveness of nitride phases in the layers deposited on bcc iron determines the accelerated kinetics of cold mechanosynthesis and the possibility of the formation of nanocrystalline iron-based solid solutions supersaturated with nitrogen and containing secondary nitrides.

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.

Effect of preliminary plastic deformation on the structure and physicomechanical properties of aging invar alloy N30K10T3

The invar alloy N30K10T3 after water quenching from 1150°C (austenite, γ phase) has the temperature of the start of martensitic transformation Ms ≈ −80°C and the Curie temperature TC ≈ 200°C. The effect of aging-induced phase decomposition in a deformed supersaturated solid solution on its hardness HV, electrical conductivity σ, magnetic permeability μ, and linear expansion coefficient β has been studied. It has been shown that cold plastic deformation of the alloy (at 20°C) to 30–50% increases its hardness, virtually does not change the conductivity, and decreases permeability. Aging of the deformed invar results in increasing HV and σ and decreasing μ. At room temperature, the deformed invar has a low linear expansion coefficient; its magnitude grows the faster, the greater the aging temperature Ta. Plastic deformation increases the density of dislocations, which form a banded substructure in austenitic grains. Besides, a metastable martensitic phase has been observed, which undergoes a reverse martensitic transformation into austenite upon heating in the temperature range from 550°C to 650°C. This transformation causes a decrease in the linear expansion coefficient β(T) of the deformed material. In samples aged at Ta = 700°C (after deformation), an athermal aging-induced martensite (αa phase) appears after cooling them to 20°C. The appearance of the αa phase is due to an increase in the temperature of the start of the martensitic transformation to above the room temperature caused by aging. In the samples containing the αa phase, there is observed a decrease in β in the temperature range from 350 to 670°C, which is due to the reverse transformation of the aging-induced martensite into austenite (αa → γ).