D. I. Davydov

The structure and magnetic properties of a heat-resistant nickel-base alloy after a high-temperature deformation

The structure of a turbine blade made of the ChS-70V alloy has been studied after operation in an experimental regime at 880°C. A considerable change in the structural state of the alloy indicates the presence of an extremely high level of stresses in the material. During the operation, the magnetic susceptibility of the alloy increases by two orders of magnitude. The possible structure objects responsible for a change in the magnetic susceptibility are the complexes of superstructure intrinsic stacking faults inside the intermetallic phase.

Phase diagram of the Co–Al–W system. structure and phase transformations near the Co3(Al, W) intermetallic composition range

Low-temperature portion of the polythermal section for the Co–Al–W system in the vicinity of the Co3(Al, W) intermetallic composition has been studied experimentally using electron microscopy and hightemperature X-ray diffraction analysis. Low-temperature structural phase transformations and temperature ranges of the existence of phases have been determined. The morphology of Co3(Al, W) intermetallic particles was studied as a function of the tungsten content in alloys.

Study of magnetic properties and structural and phase transformations in the Co-19 at % Al-6 at % W alloy

The Co-19 at % Al-6 at % W alloy prepared by two methods of melting in an inert atmosphere, namely, by arc melting followed by casting into a water cold copper mold and induction melting followed by casting in a ceramic (Al2O3) mold, has been studied. It was found that the phase composition of the alloy and its magnetic properties depend on the cooling rate of ingot after melting. Samples are ferromagnetic up to 800°C; the specific magnetization equal to σ= 10 emu/g is retained up to ∼700°C. The Curie temperatures of all phases found in the alloy have been determined. It was found that the formation of the Co7W6 phase in the alloy increases the coercive force of the alloy, whereas the saturation magnetization demonstrates a 1.5-fold decrease.

Structure and mechanical properties of an Ni3Al single crystal upon high-temperature deformation

Structure and strength properties of single-crystal 〈001〉 samples of Ni3Al have been studied in the as-grown and homogenized state during tensile tests in the temperature range of 1150–1250°C. At the strain rate of 1.32 mm/min (2 × 10−5 m/s), the samples are in the state of superplasticity. The basic mechanism of relaxation is dynamic recovery; in some regions of the sample, recrystallized grains are formed. At 1250°C, coarse twins are observed in the zone of fracture, which indicates the “switching on” of additional slip systems necessary to guarantee the relaxation process.

Structure and magnetic properties of a Ni3(Al, Fe, Cr) single crystal subjected to high-temperature deformation

The structure and magnetic properties of the Ni3(Al, Fe, Cr) single crystal subjected to high-temperature tensile deformation to failure at 850–900°C have been studied. No recrystallized grains and metastable phases were found. The rupture zone of the alloy subjected to deformation (at 900°C) to the highest degree demonstrates the fragmentation accompanied by rotation of atomic layers and changes of the chemical composition in the nickel and aluminum sublattices. Magnetic studies of the alloy have shown the existence of two Curie temperatures for samples cut from the rupture zone. Samples cut away from the rupture zone exhibit no additional magnetic transitions; twines and planar stacking faults in the alloy structure. The alloy deformed to the lower degree of deformation (at 850°C) also demonstrates twins; no ferromagnetic state was found to form.

Study of the martensitic transformation in the Co–9 at % Al alloy

Phase transformations in the Co–9 at % Al have been investigated after slow furnace cooling. It has been shown that the structure and phase composition of the alloy after slow cooling do not correspond to the equilibrium phase diagram of the alloy of this chemical composition. It has been established that the α → ε martensitic transformation does not require overcooling and occurs even during a slow cooling of the alloy. It has been found that the formation of 4H modulated martensite is a specific feature of the binary alloys of cobalt and is not connected with the rate of their cooling. The Curie temperatures for the B2, α, and ε phases have been determined.

Investigation of the structure of two heat-temperature nickel-based alloys after high-temperature deformation

The structural tests of turbine blades made from two commercial high-temperature nickel-based alloys were carried out after their test operation at elevated temperature and stresses. Both alloys contain 40% of a hardening intermetallic phase and the upper operating temperature of both alloys is limited to 900°C, but they have a different resistance to high-temperature deformation.

Analysis of the Deformation Process in Ni3(Al, Fe) Intermetallic under Longitudinal Bending

The structure and magnetic properties of an Ni3(Al, Fe) single crystal after high-temperature rolling deformation have been studied. It has been shown that high-temperature rolling deformation induces longitudinal bending in Ni3(Al, Fe), which is accompanied by the nonuniform distribution of stresses along the length of the sample. It has been found that longitudinal bending leads to change in either the mechanical or physical properties of the metal. Dynamic recrystallization has been found to occur at high degrees of deformation (starting at 40%). Local change in the distance between nickel and aluminum atoms, as well as the chemical composition, that takes place in the bending zones (distortions) of a crystal lattice of Ni3Al intermetallic compound is accompanied by change in the saturation magnetization and Curie temperature.

Effect of deformation martensite on the electrical and magnetic properties of plastically deformed chromium–nickel steel

Connection between the structural and phase changes in specimens of chromium–nickel austenitic steel and their magnetic and electrical properties has been studied. It has been established that electric resistivity can be used as an additional testing parameter for the phase composition of plastically deformed articles made of austenitic-ferritic steel. It has been shown that the emergence of an additional phase of strain-induced martensite leads to a significant increase in electric resistivity.

Heat-resistant alloys based on intermetallic Co3(Al, W)

The structures and phase compositions of a series of Co–9 at % Al–x at % W alloys (where x = 4.6, 6.8, 8.5, 10.0, 12.6) have been studied. All of them are dominated by the structure γ + γ′, with the content of other phases (the μ phase and the phase D019 based on Co3W) being insignificant. With increasing tungsten content of the alloy (to 10 at % W), the volume fraction of the γ′ phase increases, and so does its degree of long-range order. The alloy that is optimal in structure and mechanical properties has the composition Co–8.2 at % Al–8.5 at % W. The dissolution range of the γ′ phase was determined as 920–1054°C. Young’s moduli of cobalt alloys exceed E of commercial nickel-based superalloys. The samples of the studied alloys are in the ferromagnetic state with a Curie temperature of 870°C. With increasing tungsten content of the alloy, its saturation magnetization decreases and the coercive force increases. The coercive force is minimal in an as-cast sample and increases as it is subjected to deformation or heat treatment.