Laws of the deformation and failure of molybdenum in creep with grain-boundary activation by diffusional nickel fluxes

The diffusion of nickel from the surface of polycrystalline molybdenum influences the crack formation and plastic deformation in creep. Investigation shows that diffusional fluxes of nickel from the surface reduce the critical deformation at which the first cracks appear in molybdenum. The contribution of grain-boundary slip to the deformation of molybdenum in creep is considerably increased in the presence of nickel diffusion from the surface as a result of easier crack formation and grain-boundary activation.Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 16–21, July, 1992.     

Serrated creep and spatio-temporal structures of macrolocalized plastic deformation

The dynamics and morphology of macrolocalized deformation bands have been investigated using a complex of high-speed in situ methods under the conditions of serrated creep of flat samples of the aluminum-magnesium alloy 5456 with different aspect ratios. It has been found that, at the front of a macroscopic plastic deformation jump, a complex structure of propagating deformation bands, which are considered as macrolocalized deformation “quanta,” is spontaneously formed in the material. It has been shown that, with an increase in the sample length, the deformation behavior of the alloy tends to the state of self-organized criticality.     

Effects of grain boundary diffusion of copper on nickel creep

We have investigated the effects of surface copper diffusion on the creep of large-grain nickel (average grain size about 20 m) and submicron crystalline nickel (grain size about 0.3 m). For both structural states of nickel we find an acceleration of creep over its value in vacuum, and an increase in plasticity during creep when copper has diffused deeply into the nickel from the surface. The temperature range over which these effects are observed in the submicron nickel is nearly 300° lower than that for the large-grain samples. This result is probably due to a significant increase in the grain-boundary and bulk diffusion coefficients of copper in submicron nickel when compared with large-grain nickel.Siberian Branch. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 83–86, December, 1994.     

Investigation of grain-boundary diffusion of nickel in molybdenum by auger electron spectroscopy

The dependence of the grain-boundary diffusion coefficient of nickel in molybdenum on annealing temperature was investigated. Possible causes are analyzed for differences in the values of the grain-boundary diffusion coefficients and the activation energies for this process from those obtained by earlier researchers.Institute of the Physics of Strength and Materials Science, Siberian Branch, Russian Academy of Sciences (SO RAN). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 28–31, July, 1992.     

Variation of the ultrasonic velocity in al under plastic deformation

Variation of the velocity of ultrasound propagation in polycrystalline aluminum under plastic deformation is studied. The dependences of the velocity of ultrasound on the strain and the actual stress are found to consist of three distinct stages. The study of the complex shapes of these dependences allows one to reveal additional stages in the parabolic stress-strain curve of the plastic flow, these features being impossible to observe by conventional methods. The behavior of the ultrasonic velocity observed in the experiment is explained by the changes in the defect structure of the material under deformation.     

Single-phase model of recrystallization of molybdenum activated by diffusion of nickel impurities

A new model of the activated recrystallization of molybdenum under the diffusion action of a nickel coating is proposed. In the context of this model, dependences of the thickness of the recrystallized layer and of the velocity of motion of the recrystallization front on the annealing time have been derived analytically. It has been revealed that an increase in nickel concentration on the surface increases, whereas an increase in average size of recrystallized grains decreases the recrystallization velocity in molybdenum. A temperature dependence of the thickness of the recrystallized molybdenum layer has also been derived. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 50–55, November, 2007.     

Grain size-dependent diffusion activation energy in nanomaterials

We report a unified model, free of any adjustable parameter, for size-dependence of intrinsic diffusion activation energy of elements in crystals. It is found that as the size of the nanocrystals decreases, the diffusion activation energy of atoms decreases and the corresponding diffusion coefficient strongly increases due to the Arrhenius relationship between them, which leads to evident diffusion at the room temperature. The model prediction is in agreement with the experimental diffusion results of N into bcc Fe and Ag into Au nanoparticles.     

The influence of plastic deformation on the magnetostriction constant of nickel

The magnetostriction constant of nickel was measured as a function of plastic deformation up to an elongation of 30%. The values of the magnetostriction constant in deformed samples deviate considerably, a fact which cannot be explained by errors of measurement. The absolute value of the magnetostriction constant decreases with increasing plastic deformation (by around 5%).

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30% . , . ( 5%).

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In conclusion the authors thank J. Kaczér, C. Sc. and B. esták, C. Sc. for carefully reading the paper and for their remarks, J. Míová for help in the measurements and workers of the chemical department of our Institute for careful preparation of the samples.     

Effect of intermediate plastic deformation on the high-temperature creep and lifetime of aluminum

The effect of various types of intermediate plastic deformation on the high-temperature creep of polycrystalline aluminum is studied. Intermediate deformation is performed after testing for 0.44 of the time to failure t _f via the single or multiple action of a hydrostatic pressure of 1000 MPa on porosity or via tension or compression at atmospheric pressure. Intermediate deformation is shown to decrease the creep rate, to increase the time to failure, and to increase the grain size. The change in the creep rate is maximal upon the cyclic (in the same test time intervals) action of pressure. A relation between the creep rate and the grain size has been reveled. The detected decrease in the creep rate is assumed to be caused by a decrease in the density of mobile dislocations (due to recrystallization).     

Contribution of surface tension energy during plastic deformation of nanomaterials

The surface tension energy of crystallites in polycrystalline materials having different microstructures and in nanomaterials has been estimated. A hypothesis is proposed, according to which the yield stress of materials is determined by the balance of elastic energy and the surface tension energy of crystallites. The independently measured value of surface energy can be used to estimate the yield stress of polycrystalline materials.     

Quantum mechanical activation energy of vacancy diffusion in crystals

This report examines the quantum mechanical mobility of vacancies in cubic crystals using the Morse potential. Nonadiahatic effects in vacancy diffusion are considered. Analytic expressions for the probability of a diffusive jump and for the activation energy are derived.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 29–32, April, 1988.     

Study of diffusion creep accompanying superplastic deformation of the alloy ZhS6KP

The development of diffusion creep (DC) accompanying superplastic deformation (SPD) of the highly doped nickel alloy ZhS6KP is studied based on an investigation of the redistribution of dispersed intragrain deposits of the phase of Ni₃(Al, Ti). Deposit-free zones (DFZ) are formed in the alloy, held at the temperature of SPD and accompanying deformation at the grain boundaries. The contribution of DC to the deformation was determined from a comparative analysis of the width of the DFZ in the deformed and undeformed parts of the samples for different grain sizes and rates of DC taking into account diffusion accommodation. It was established that for the optimum rate of SPD the upper limit of the contribution of DC to deformation for 2-m grains does not exceed 11%. It is concluded, based on the distribution of DFZ, that the effect of DC accompanying SPD is determined by diffusion fluxes, associated with the local concentration of stress accompanying the development of grain-boundary slipping.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 40–45, June, 1986.In conclusion, we thank Yu. M. Mishin for a useful discussion of the results.     

High-temperature creep of nickel under conditions of grain-boundary diffusion of impurities from the surface

Comparative investigations of the effect of diffusion streams of copper atoms (a weakly segregating impurity) and silver atoms (a strongly segregating impurity) from the surface in the high-temperature plastic deformation of nickel have been carried out. It has been established that in the high-temperature plastic deformation of nickel, when there are diffusion streams of copper and silver from the surface, there is a reduction in the creep resistance of nickel due to an increase in the contribution of grain-boundary slip to the overall deformation. Two stages, characterized by different values of the rate sensitivity factor m, are observed on the curve of the stress against the rate of deformation over a certain temperature range for each impurity. In the region of deformation rates of sec⁻¹, m≊0.2, and for sec⁻¹, m becomes less than 0.05. Institute of Physics of the Strength and Study of Materials. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 119–125, July, 1997.     

Effect of plastic deformation and quenching on the absolute thermal emf of nickel

The effect of the degree and rate of plastic deformation of nickel on the change of its absolute thermal emf was studied. The dynamic effect of the change of thermal emf was established, the dynamic coefficient being 1.22–1.25. Plastic deformation of quenched nickel reduced its absolute thermal emf, on the basis of which conclusions are drawn about the contributions, different in sign, of holes and dislocations to the change of the absolute thermal emf of nickel. The kinetics were studied of the recovery of the thermal emf induced in nickel by plastic deformation, and the existence was established of two stages of recovery, differing in nature and with different activation energies, 0.1 and 0.3 eV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 77–81, June, 1971.     

Variation in electromagnetic radiation during plastic deformation under tension and compression of metals

This paper presents some significant variations in the intermittent electromagnetic radiation (EMR) during plastic deformation under tension and compression of some metals with selected crystal structure, viz. zinc, hexagonal closed packed (hcp), copper, face-centred cubic (fcc: stacking fault energy 0.08 J/m²), aluminium (fcc: stacking fault energy 0.2 J/m²) and 0.18 % carbon steel, body-centred cubic (bcc). The intermittent EMR signals starting near yielding are either oscillatory or exponential under both modes of deformation except a very few intermediate signals, random in nature, in zinc under compression. The number and amplitude of EMR signals exhibit marked variations under tension and compression. The smooth correlation between elastic strain energy release rate and average EMR energy release rate suggests a novel technique to determine the fracture toughness of metals. The first EMR emission amplitude and EMR energy release rate occurring near the yield increase, but maximum EMR energy burst frequency decreases almost linearly with increase in Debye temperature of the metals under tension while all EMR parameters decrease nonlinearly under compression. These results can be developed into a new technique to evaluate dislocation velocity. The EMR amplitude and energy release rate of the first EMR emission vary parabolically showing a maxima with increase in electronic heat constant of the metals under tension while they first sharply decrease and then become asymptotic during compression. However, the variation in EMR maximum energy burst frequency is apparently similar under both modes of deformation. These results strongly suggest that the mechanism of EMR emission during plastic deformation of metals involves not only the interaction of conduction electrons with the lattice periodic potential as presented in the previous theoretical models but also the interaction of conduction electrons with phonons. However, during crack propagation and fracture, charge oscillations at fractured surfaces due to breaking of atomic bonds constitute an additional factor.     

Dynamics of plastic deformation: Waves of localized plastic deformation in solids

Conclusions It has been shown here that a localized plastic deformation in structurally inhomogeneous media can be of a wave nature and can propagate in the form of nonlinear plastic waves, not only at the microscopic level but also at the mesoscopic level. It has been established that there is an interrelationship between this new effect and grain-boundary slippage (an effect which has been under study for a long time) and also with certain types of quasiviscous fracture in plastically deformable materials.We have discussed certain specific practical problems in the mechanics of plastic deformation, and for certain types of fracture. In the future, these problems will be discussed at a more profound level and in greater detail, because of experimental studies which are presently being carried out on the dynamics of deformation for various types of loading and fracture [17, 18, 31]. We hope that the approach proposed here for a theoretical study of the localization of deformation and fracture can be taken to study such effects as splitting off [31], the influence of defect fluxes on grain-boundary slippage [22], superplasticity [23], the behavior of tectonic faults and boundaries of various types [32], electroplastic and magnetoplastic effects, and high-temperature localization of deformation [25].The general nature of the approach proposed here results from the circumstance that a localization of deformation is present explicitly or implicitly during plastic deformation, and the behavior of this deformation plays a role of fundamental importance in the propagation of plastic deformation through a material.The author wishes to thank V. E. Panin for a constant discussion of this problem and I. O. Nedavnii for carrying out the numerical calculations.V. V. Kuibyshev Tomsk State University. Institute of Strength Physics and Materials Science. Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 19–41, April, 1992.