R. R. Mulyukov

Effect of ultrasonic treatment on the structure and properties of ultrafine-grained nickel

Effect of ultrasonic treatment on the microstructure, microhardness, and thermal stability of nickel subjected to high-pressure torsion (under a quasi-hydrostatic pressure of 6 GPa) has been studied. It has been demonstrated that ultrasound favors a considerable decrease in internal microstresses. It has been found that after an ultrasonic treatment, the grain growth proceeds at higher annealing temperatures than it does in ultrafine-grained nickel that has not been subjected to ultrasonic treatment.

Computer simulation of the effect of ultrasound and annealing on the structure of a two-dimensional severely deformed nanocrystalline material

Qualitative comparison of the effect of ultrasonic treatment and annealing on the structural relaxation of a two-dimensional nanocrystalline material after severe plastic deformation has been performed by the molecular-dynamics method. The treatments of both types lead to a decrease in the dislocation density and to a more equilibrium state of grain boundaries and triple junctions but, unlike the temperature effect, ultrasonic treatment does not result in a considerable grain growth. Thus, the calculations conducted indicate potentialities of the ultrasonic treatment of bulk nanomaterials with the aim of relieving internal stresses without increasing grain size.

Effect of severe plastic deformation on the properties of the Fe-36% Ni invar alloy

Temperature dependences of the magnetization and thermal expansion coefficient of the Fe-36% Ni invar alloy in different structural states obtained upon plastic deformation by torsion under a quasihydrostatic pressure followed by annealing at different temperatures are studied. A decrease in the thermal expansion coefficient of the invar in a temperature range of 20–100°C and the formation of ordered precipitates (with a superstructure) were found to result from severe plastic deformation.

Temperature dependences of thermal expansion and saturation magnetization in Fe(67.0%)-Ni(32.5%)-Co(0.5%) Invar alloy with nanocrystalline structure

The effect of the nanocrystalline structure of Fe(67.0%)-Ni(32.5%)-Co(0.5%) Invar alloy on its thermal expansion is considered. It is found that the structure with grain mean sizes of about 100 nm increases its temperature coefficient of thermal expansion in the range of “invarness,” i.e., in the temperature range where the alloy offers the Invar properties. Reasons for this behavior are analyzed by taking the temperature dependence of the saturation magnetization.

Effect of magnetic field on the morphology and fine structure of low-temperature martensite phase in a ferromagnetic Ni2.08Mn0.96Ga0.96 alloy

The morphology and fine structure of high-temperature austenitic and low-temperature martensitic phases in a ferromagnetic Ni2.08Mn0.96Ga0.96 alloy and the effect of magnetic field on the peculiarities of the martensite formation have been studied. The Ni2.08Mn0.96Ga0.96 alloy in the initial cast and annealed states was found to undergo martensitic and magnetic phase transformations at temperatures Ms = 280 K, Mf = 265 K, As = 280 K, Af = 295 K, and TC = 375 K, respectively. Above Ms, the alloy is in a metastable premartensitic state, which leads to a characteristic diffuse scattering and tweed contrast when studying by electron microscopy. An applied magnetic field of up to 600 kA/m was found to affect the martensitic transformation in the alloy. The field application leads to changes in the morphology and fine structure of martensite due to orientation along the field direction of the magnetizations of the energetically advantageous (in terms of the directions of the magnetization vectors) c domains of the existing orientation variants of the martensite crystals having a packet pairwise-twinned morphology. The martensitic structure of the Ni2.08Mn0.96Ga0.96 alloy already formed previously during cooling is not affected by an external magnetic field with a strength of up to 600 kA/m.

Mass-spectroscopic study of the diffusion and solubility of helium in submicrocrystalline palladium

By the method of helium thermal desorption from submicrocrystalline palladium presaturated in the gaseous phase, the diffusion coefficient Deff and solubility coefficient Ceff of helium are measured in the range P=0–3 MPa and T=293–508 K. The pressure dependence of Ceff flattens at high pressures. At low saturation pressures, the temperature dependences of the diffusion and solubility coefficients may be divided into (1) high-temperature (400–508 K) and (2) low-temperature (293–400 K) ranges described by the exponentials D1, 2=D0exp (−E1, 2D/kT) and C1, 2=C0exp (−E1, 2S/kT). The energies of diffusion activation are E2D=0.0036±0.0015 eV and E1D=0.33±0.03 eV, and the solution energies are E2S=−0.025±0.008 eV and E1S=0.086±0.008 eV in the low-and high-temperature ranges, respectively. Mechanisms behind the diffusion and solution of helium are discussed.

Improvement of mechanical properties of the Ti–45Al–5Nb–1Mo–0.2B (аt %) intermetallic alloy by means of microstructure controlling

The effect of heat and thermomechanical treatments conditions on the microstructure and main mechanical characteristics (obtained by tensile, high-temperature long-term strength, fracture toughness, and high-cycle fatigue tests) of the Ti–45Al–5Nb–1Mo–0.2B (аt %) alloy was studied. Before the treatments, the sequence of phase transformations in the alloy after its solidification was determined by testquenching method. The obtained data were used to develop conditions for the heat and thermomechanical treatments. It was found that a small but stable increase in the plasticity and strength of the cast alloy is observed after three-stage annealing at temperatures that correspond to the (α + γ)- and (α2 + β(В2) + γ)-phase region. The thermomechanical treatment at temperatures corresponding to the (α(α2) + β(В2) + γ)-phase region and subsequent two-stage annealing at temperatures that correspond to the (α + β(В2) + γ)- and (α2 + β(В2) + γ)-phase region lead to the formation of fine-grained duplex structure. This determined the substantial improvement of the low-temperature plasticity and strength (δ = 3.1% and σu = 860 MPa at 20°C, respectively) and retained high creep resistance to 700°C.

Kinetics of changes in the saturation magnetization during annealings of the Fe-36% Ni invar alloy subjected to severe plastic deformation

Changes in the saturation magnetization and microhardness of the Fe-36% Ni invar alloy with a nanocrystalline structure, which were caused by annealings at different temperatures, are studied. The nanocrystalline structure was produced by severe plastic deformation. A high-temperature ferromagnetic phase was found to result from the formation of such a structure. The temperature of annealing after which the content of the phase is maximum was determined. When analyzing the kinetics of phase-composition changes, an increase in the diffusive mobility of atoms during the formation of the nanocrystalline state in the material was taken into account.

Study of The Temperature Coefficient of Thermal Expansion and Microstructure of a 36h Submicrocrystalline Invar Alloy

In the last few years, of great interest to investigators has been the physical materiology of submicrocrystalline (SMC) materials (with average grain size of about 0.1 μm). Their elastic, thermal, electrical, magnetic, and other physical properties significantly differ from those of conventional coarse-grained materials [1–4]. In this connection, of great interest are investigations of invar alloys [5]. These alloys, important from the viewpoint of their practical implementation, have a temperature coefficient of thermal expansion close to zero in the temperature range of their application. In addition, they have anomalous elastic, thermal, magnetic, and other physical properties. In the present work, the characteristic features of thermal expansion of the SMC invar alloy are studied.