A. Yu. Churyumov

Study of the structure and mechanical properties of corrosion-resistant steel with a high concentration of boron at elevated temperatures

Because of the high cost of corrosion-resistant steels, a necessary condition for their production is reducing rejection at all stages of processing, including hot forming, by optimizing process parameters. In this work, the mechanical characteristics of a corrosion-resistant steel with high content of boron have been studied at elevated temperatures. Using a special complex for the physical simulation of thermomechanical processes, it has been shown that the optimum temperature range of hot compressive plastic deformation is 950–1100°C. A mathematical model has been constructed, which relates the yield stress to the parameters of the process of hot plastic deformation. During deformation in the range of 850–1150°C, the boride particles present in the steel become oriented perpendicular to the compression axis; at high temperatures, the spheroidization of titanium diborides occurs, which reduces their size.

Structure and mechanical properties of Ni-Cu-Ti-Zr composite materials with amorphous phase

The structure of specimens of Ni-Cu-Ti-Zr alloys with an amorphous phase has been examined by X-ray diffraction, as well as by transmission and scanning electron microscopy. Mechanical characteristics of the alloys have been determined using universal testing machines. Transformation-induced plasticity has been found to exist. The specimens demonstrate a good combination of strength and plasticity owing to both the composite effect of a heterophase structure and the dynamic martensitic transformation that develops during deformation.

Development of mathematical models of superplasticity properties as a function of parameters of aluminum alloys of Al-Mg-Si system

The article discusses the superplasticity properties and structure parameters of cold-worked alloys of a quasi-binary section of the Al-Mg-Si system with a volume fraction of eutectic particles of 0.08–0.18. Mathematical models of yield stress and effective elongation as a function of the structure and engineering parameters have been developed for alloys of this system. An analysis of the developed models shows that, in the temperature range of 520–560°C, superplastic deformation is controlled by the rate of diffusion of aluminum atoms in the grain bulk.

Search for promising compositions for developing new multiphase casting alloys based on Al-Cu-Mg matrix using thermodynamic calculations and mathematic simulation

A calculation-experimental study is carried out to improve the concept of searching for new alloying systems in order to develop new casting alloys using mathematical simulation methods in combination with thermodynamic calculations. The results show the high effectiveness of the applied methods. The real possibility of selecting the promising compositions with the required set of casting and mechanical properties is exemplified by alloys with thermally hardened Al-Cu and Al-Cu-Mg matrices, as well as poorly soluble additives that form eutectic components using mainly the calculation study methods and the minimum number of experiments.

Studies of the structure and mechanical properties of Ti43.2Zr7.8Cu40.8Ni7.2Co1 alloy containing amorphous and crystalline phases

The structure and mechanical properties of Ti43.2Zr7.8Cu40.8Ni7.2Co1 alloy cast into a massive copper mold are studied. It has been shown that, after the fast cooling of the alloy, the structure consists of amorphous matrix and crystal particles distributed in the matrix; hence, the alloy displays high strength (higher than 1600 MPa) and relatively high plasticity (1%). Modeling the strain of the alloy using the finite elements method has shown that the crystal particles in the amorphous matrix are effective barriers for the propagation of shear bands, thus stimulating nucleation and the development of new shear bands and increasing the plasticity of the material in general.

Study of the structure and properties of a wrought Al–Mg–Mn aluminum alloy on a Gleeble 3800 simulator designed for physical modeling of thermomechanical processes

The mechanical behavior of aluminum alloy 5454, belonging to the system Al–Mg–Mn, is studied during hot plastic deformation on a Gleeble 3800 simulator designed for physical modeling of thermomechanical processes. The study was conducted under different temperature-rate conditions. Examination of the structure of the hot-deformed specimens showed that dynamic recrystallization is impeded in the alloy. The substructure obtained after deformation at 400°C consists mainly of equiaxed subgrains with dimensions of 1–2 μm, the exact size depending on the rate of deformation. A mathematical model that was constructed to relate the flow stress of the given alloy to the rate, temperature, and degree of deformation can be used for finite-element calculation of the properties of different sections of products of complex shape that are made of this alloy by various methods of hot plastic deformation.

Comparative analysis of the structure of palladium-based bulk metallic glasses prepared by treatment of melts with flux

A comparative analysis has been presented of structural features of palladium-based bulk metallic glasses prepared by argon gas casting into a copper mold after treatment of melts with a flux and studied using X-ray synchrotron radiation. The radial distribution functions have been calculated. The short-range order (in the first and second coordination shells) and the medium-range order (from the third to several subsequent coordination shells) in atomic arrangement have been analyzed.

Analysis of softening alloys of the Al-Ni system containing particles of variable dispersity

Regularities of the deformation strengthening and softening of aluminum alloys containing second-phase Al3Ni particles 0.3 to 2.2 μm in size with a volume fraction from 0.03 to 0.1 are investigated during cold deformation and subsequent annealing at 0.6tm. It is shown that the largest hardness increment is observed for alloys with a maximal fraction of fine particles (d = 0.3 μm) after rolling deformation larger than 0.4. Fine particles prevent the development of crystallization upon true deformation up to 2.3, thereby effectively inhibiting softening. An increase in the particle size to 1.2–2.2 μm stimulates nucleation during recrystallization, substantially accelerating this process. For example, in order to ensure recrystallization uniformly over the entire sheet volume at d = 2.2 μm, cold deformation with ɛ = 0.4 is sufficient.

Use of a physical approach and artificial neural networks for the simulation of the relation between the yield strength of quenched Al-Si alloys and their structural characteristics

Models are developed to relate the yield strength of Al-Si alloys to their structural characteristics. The models are based on the physical theory of strength and artificial neural networks. The simulated and experimental yield strengths agree well. It is wise to use an artificial neural network to predict the properties of alloys whose structural parameters fall in the range of the learning sample.

Influence of Al3Ni crystallisation origin particles on hot deformation behaviour of aluminium based alloys

Abstract Binary Al–Ni, Al–Mg and ternary Al–Mg–Ni alloys containing various dispersions and volume fraction of second-phase particles of crystallisation origin were compressed in a temperature range of 200–500 °C and at strain rates of 0.1, 1, 10, 30 s−1 using the Gleeble 3800 thermomechanical simulator. Verification of axisymmetric compression tests was made by finite-element modelling. Constitutive models of hot deformation were constructed and effective activation energy of hot deformation was determined. It was found that the flow stress is lowered by decreasing the Al3Ni particle size in case of a low 0.03 volume fraction of particles in binary Al–Ni alloys. Intensive softening at large strains was achieved in the alloy with a 0.1 volume fraction of fine Al3Ni particles. Microstructure investigations confirmed that softening is a result of the dynamic restoration processes which were accelerated by fine particles. In contrast, the size of the particles had no influence on the flow stress of ternary Al–Mg–Ni alloy due to significant work hardening of the aluminium solid solution. Atoms of Mg in the aluminium solid solution significantly affect the deformation process and lead to the growth of the effective activation energy from 130–150 kJ/mol in the binary Al–Ni alloys to 170–190 kJ/mol in the ternary Al–Mg–Ni alloy.