E. V. Belozerov

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⊥.

High-strength magnetically hard Fe-Cr-Co-Based alloys with reduced content of chromium and cobalt

Structure and magnetic and mechanical properties of precipitation-hardening Fe-Cr-Co-W-Ga alloys with reduced Cr and Co contents have been studied. The compositions studied go beyond the limits of the miscibility gap in the phase diagram for conventional Fe-Cr-Co alloys. It has been established that after cold plastic deformation and low-temperature annealing the alloys are characterized by high values of mechanical and magnetic characteristics, which are significantly higher than those of known analogs. It is demonstrated that the treatment suggested leads to the decomposition of homogeneous solid solution based on α-Fe with the precipitation of disperse particles of a tungsten-rich phase, which promotes strengthening of alloys.

Magnetic properties of Ni3AlxMn1 − x alloys

Paramagnetic susceptibility of alloys Ni3AlxMn1 − x in the field of the transition between the ferromagnets described in the band theory (Ni3Al) and in the spin-localized (Ni3Mn) model of magnetic moments has been investigated. The concentration dependences of the paramagnetic Curie temperature, effective magnetic moment, and temperature-independent component of magnetic susceptibility have been determined.

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 transformations in high-strength magnetically hard Fe-Cr-Co-W-Ga alloys

Processes leading to a high-coercivity state of W and Ga containing Fe-Cr-Co alloys that possess a required strength and plasticity have been investigated. The effect of W and Ga additions on the structural constituents formed due to the decomposition of a high-temperature solid solution has been studied by the methods of X-ray diffraction, electron microscopy, and Mössbauer spectroscopy. The role of cold deformation preceding low-temperature annealings has been clarified.

Effect of tungsten and gallium on the structure and magnetic and mechanical properties of Fe-Cr-Co alloys

Effects of the alloying additions of W and Ga, cold deformation, and regimes of heat treatment on the magnetic and mechanical properties of precipitation-hardening Fe-Cr-Co alloys have been investigated. It has been shown that the alloying with tungsten leads to a strengthening of the α solid solution and an additional jumplike increase in strength after deformation and age hardening. The coercive force grows simultaneously with an increase in strength; the structure of the alloy in this case contains a large concentration of linear defects (dislocations), which indicates an important contribution of magnetoelastic energy to the formation of the high-coercivity state and of elastic strains to the increase in the strength properties. The character of fracture becomes brittle. The modifying of the alloy with gallium leads to an increase in plasticity due to the dispersion of the structure, formation of retained austenite in it, and formation of an interphase layer more uniform in composition. The character of fracture changes from brittle to brittle-ductile. A high-strength magnetically hard material has been obtained with Hc = 90–125 A/cm, σm = 120–130 G cm3/g, Br = 0.6–0.65 T, σ0.2 = 1300–1600 MPa, and δ = 2.0–4.6%.

Features of the Post-Deformation Hardening of Fe-Cr-Co Hard Magnetic Alloys with W and Ga Additives

The structure, mechanical and magnetic properties have been studied for Fe-Cr-Co-based hard magnetic alloys with W and Ga additives, subjected by the quenching and post-deformation hardening. The alloys combine the properties of the hard magnetic material with outstanding mechanical strength and plasticity. Using X-ray and electron microscopy analysis, the reasons and conditions of formation of these properties have been determined.

Effect of gallium on the crystal structure and magnetic properties of PrFe11 − x GaxCy compounds

A homogeneity range of the PrFe11 − xGaxCy phase was determined. As the gallium content increases, the lattice parameters were shown to increase, whereas the Curie temperature decreases; the type of magnetic anisotropy at room temperature is unchanged. In the alloys with x > 3, the transformation of the tetragonal lattice of the compound into an orthorhombic lattice with the axial ratio a/b ≤ 1.006 is observed. This is likely to be caused by the ability of gallium to form covalent bonds. Gallium atoms were found to occupy preferentially 16j2 and 4e2 sites in the orthorhombic lattice of the FePr6.5Ga4.5C compound. The atoms located in the 16j2 sites form wavy chains along the [010] direction of the orthorhombic lattice, whereas the iron atoms located in the 16j1 sites form analogous chains along the [100] direction. Owing to this fact, one of these directions is likely to become an easy axis. The alloy with x= 4.5 has a low coercive force at room temperature; at 114 K, its coercive force is Hc = 42.4 kA/m.

Martensitic transformations γ-ɛ (α) and the shape-memory effect in aging high-strength manganese austenitic steels

Changes in the structure, mechanical properties, kinetics of martensitic transformations, and amount of reversible deformation in precipitation-hardening high-strength shape-memory steels (20Mn-2Si-V with 0.2–1.0% C) strengthened as a result of carbide aging, intense warm deformation, and rapid crystallization from the melt have been studied.

The role of plastic deformation in the creation of high strength in hard magnetic alloys Fe-Cr-Co-W-Ga

The influence of plastic deformation preceding low-temperature aging on the structural factors that determine the strengthening of the Fe-15Cr-13Co-8W-0.5Ga and Fe-22Cr-l5Co-9W-0.5Ga alloys has been studied. The reasons are discussed for the necessity of employment of different strains to achieve the high-strength state in alloys with different contents of chromium and cobalt.