N. N. Stepanova

Ordering kinetics in ternary Ni3Al-X alloys

Abstract Measurements of electrical resistivity were used to study the kinetics of ordering in stoichiometric Ni 3 Al alloyed with a third element (Nb, Ti, V, W, Cr, Co, Fe). The activation energies of ordering and disordering were found.

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.

Structure formation in 〈001〉 single crystals of a nickel-based superalloy solidified with TiCN powder addition

Abstract The solidification structure and tensile properties of single crystals of nickel-based superalloy have been examined as influenced by additions of ultra dispersed powder of titanium carbonitride to the melt before solidification. Two variants of alloy (carbon-containing and low carbon) were studied. The addition has been found to change the morphology and chemical composition of the carbide phase in the carbon-containing alloy and to affect the dissolution of the strengthening γ′-phase in the low carbon alloy. Solidification with addition leads to an increase of creep-rupture life of single crystal samples, especially for the low carbon variant.

Influence of solidification conditions on γ′-phase thermal stability in 〈001〉 single crystals of Ni-based superalloys

Operating conditions for details of the nickel-based superalloys under long-term high-temperature loading necessitate high thermal stability of the alloy structure as a whole and {gamma}{prime}-phase especially, as the latter is an essential factor of the alloy strengthening. The direct investigation of the phase stability of superalloy specimens in the range of operating temperatures is of major interest. In the present work high-temperature X-ray technique was used to study the {gamma}{prime}-phase thermal stability upon heating in the temperature range from 20 C to 1200 C for a series of single crystal specimens of nickel-based superalloy ZhS 26 obtained using various regimes of the melt overheating before solidification.

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.

Ultrasonic testing of single- and polycrystal articles made of nickel-based heat-resistant alloys

The acoustic properties of single-crystal and polycrystalline heat-resistant nickel-based alloys are considered. Specimens of industrially produced ЦHK-8MP, ЧС-70B, and VKNA-4U alloys are studied. The velocities of ultrasonic waves and the attenuation coefficients are measured. The possibility of detecting artificial reflectors of the flat-bottom-hole and side-drilled-hole types located at different depths is shown. A reflected signal from a crack in a blade manufactured from the ЧС-70B alloy is studied. Recommendations on the selection of the parameters of ultrasonic testing of articles made from heat-resistant alloys are given.

Velocities of elastic waves and the elasticity moduli of nickel-base superalloys and of the 60N21 alloy

Measurements of velocities of elastic waves have been performed in polycrystalline samples of an intermetallic compound Ni3Al, this intermetallic compound alloyed with niobium or cobalt, superalloys ZhS36 and VKNA-4U, and the 60N21 alloy. Elasticity moduli have been calculated, namely, Young’s modulus, shear modulus, bulk modulus, and the Poisson ratio. The results obtained are compared with those calculated from the tensor of the elasticity moduli obtained for single crystals. The calculations have been performed in the Voigt and Reuss approximations.

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.