Polycrystal creep in the microplastic stress range

A microcreep theory has been developed for polycrystalline materials, which incorporates the microplastic strain in the aggregate on static loading. Experiments have been performed on the creep laws for polycrystalline metals and alloys, and it is found that the theory fits the experiments. The mobile-dislocation density decreases during microcreep.V. D. Kuznetsov Siberian Technical Physics Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 25–29, June, 1993.     

Effect of chromium on structure,strength, and plasticity of high-temperature intermetallide Ni3Al

The effect of chromium on structure, strength characteristics, plasticity, and failure principles in the polycrystalline intermetallide Ni₃Al, produced by self-propagating high-temperature synthesis, is studied over the temperature range 290–1270 K. It is shown that the effect of chromium depends upon which element (nickel or aluminum) it is introduced in place of, although failure of alloys with various chromium contents at all deformation temperatures remains intercrystallite in nature.V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 30–36, June, 1993.     

Influence of nonhydrostatic stresses on the development of martensitic transformations and inelastic strains at various levels in Ti(Ni-Cu-Fe) polycrystalline intermetallic compounds

The levels of inelastic martensitic strain of polycrystals during a thermoelastic martensitic transformation under a load are discussed. The example ofTi(Ni-Cu-Fe) alloys with the B2 structure was used to study the role of microlevel and mesolevels in inelastic martensitic deformation during cooling of polycrystals under a load and loads in different initial structural states. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Institute of Physics of Strength of Materials and Materials Science, Siberian Branch of the Academy of Sciences of the USSR, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, p. 35–46, January, 1998.     

Fatigue failure mechanism of polycrystalline materials at the mesoscopic level

Systematic studies of the mesoscopic mechanisms of deformation of polycrystalline materials of lead and its alloys have been carried out under conditions of sign-alternating bending at room temperature. It has been shown that fatigue failure is due to the evolution of vortices of mesoscopic substructures. Multiple slip separated in adjacent grains is the basis for this kind of deformation. This causes extremely strong localization of the displacement in individual favorably oriented grains and self-organization of these grains in agreement with regular structural levels of deformation. In polycrystalline lead, the mesoscopic substructure has a block character, with each block containing several grains. The elements of such substructures are nucleated in stress mesoconcentrator zones which arise at the grain boundaries under conditions of intense grain boundary slippage. In the course of cycling they gradually propagate through the whole transverse cross section of the sample, which completes its failure. Alloying substantially changes the character of the mesoscopic substructures which are formed. We have considered the different types of vortex mesoscopic substructures and studied their connection with cyclical endurance of the alloy. Recommendations for increasing the fatigue endurance of plastic polycrystalline materials are given. Institute of the Physics of hardening and Materials Science, Siberian Section, Russian Academy of Sciences. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 40–57, June, 1996.     

Defect microstructure in titanium nitride submicrocrystals

Transmission electron microscopy has been applied to the defect structure of titanium nitride in the submicrocrystalline (SMC) state produced under conditions of deviation from equilibrium in ion-plasma synthesis. The submicrocrystals contain a new type of defect substructure having a continuum disclination density up to 2.5 rad/μm². Direct structure methods give evidence for a high density of partial disclinations at the SMC grain boundaries in the nitride phase. A novel method has been used to examine substructures having a high defect density, which has been used to estimate the partial disclination density at the submicrocrystal boundaries. The origin of this highly defective state and the effects of it on the properties of SMC materials is discussed. Kuznetsov Siberian Technical Physics Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–12, July, 1998.     

Structure and mechanical and electrochemical properties of ultrafine-grained Ti

A study is conducted into the microstructure and physico-mechanical properties of ultrafine-grained titanium produced by severe plastic deformation using the method of equichannel angular pressing. The effects of thermal and mechanical treatment on these characteristics are investigated. The possibility of forming mechanical properties in titanium that compare well with those of highly doped titanium alloys is shown. Institute for Strength Physics and Materials Science; Siberian Physical-Technical Institute at Tomsk State University; Institute of Physics of Advanced Materials at UFA Aviation Technology University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 77–85, January, 2000.     

Shear strength of metals behind shock fronts

Results are presented from a numerical modeling of experiments, conducted by J. Lipkin, R. Asay, L. Chabildas, and J. Wise, in which shock-compressed aluminum and polycrystalline beryllium were loaded again by shock waves. Reproduction of the experimental structures of the impulses in the calculations made it possible to determine the stresses acting in the materials during the primary and secondary shock loading, as well as to study the dynamics of the secondary shock load. It is shown that resistance to plastic strain is maintained in aluminum and beryllium behind the front of weak shock waves with intensities up to 10 GPa. The shear strength of the material behind the front does not correspond to the shear stresses at the Hugoniot elastic limit. For aluminum alloy 6061-T6 and beryllium, shear strength behind the fronts of shock waves with amplitudes up to 10 GPa is lower than in the elastic precursor but is greater than the static yield point of the material in the initial state.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 62–66, October, 1995.     

Anomalous mass transfer and phase and structural changes in α-Fe when acted upon with electron pulses

The phase composition and the defect structure of armco-iron irradiated with a relativistic electron beam is investigated using electron microscopy and x-ray structural analysis. Specimens with a chromium coating and without it were irradiated.Tomsk State University Architecture-Building Academy. Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 95–99, April, 1994.     

Structural and phase transformations in Ni3Fe during high-dose ion implantation

The results are given for experimental studies of the structural-phase state formed in the surface and nearsurface layers of a disordered polycrystalline Ni₃Fe alloy during high-dose ion implantation. The studies used Auger electron spectroscopy, transmission electron microscopy, x-ray structural analysis, and microhardness measurements. The ion implantation was done using the “Raduga” vacuum arc source with a multicomponent cathode of composition Zr (89.5 wt. %)+C+N+O with an acceleration voltage of 50 kV. The implanted ion dose was varied in the range (6.0·10¹⁶–6.0·10¹⁷) ions/cm². It was established that in the surface layer which is alloyed during ion implantation there is amorphization with simulataneous formation of finely dispersed ZrO₂ particles whose dimensions increase with increasing implanted ion dose; this is accompanied by an increased internal mechanical stress. Beyond the ion-implanted layer a sublayer about 10 μm thick with a high dislocation density is formed (the “long-range action” effect). The results of microhardness measurements correlate with the data from structural studies. Institute of the Physics of Strength and Materials Science, Siberian Section, Russian Academy of Science; Tomsk State University—Architectural-Construction University; and Scientific Research Institute for Nuclear Physics at Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 15–24, November, 1998.     

Creep and diffusion parameters in submicrocrystalline metals

We have studied the creep of nickel and copper in a submicrocrystalline (SMC) state in a vacuum and in the presence of a diffusion contact with an impurity (Cu and Al, respectively). It is shown that a reduction of the resistance in the presence of a diffusion contact with an impurity is observed in the SMC materials in the temperature range 398 to 473 K. This range is 200 to 400 K lower than the corresponding range for coarse-grained material. It is shown that in this temperature interval the coefficients of grain boundary diffusion for copper in SMC nickel are 5 to 6 orders of magnitude larger than in the coarse-grained material. We propose that the reduction in the temperature for the manifestation of a creep activation effect in the presence of a diffusion contact with an impurity in SMC materials is caused by the increase in the diffusion permeability of the submicrocrystalline grain boundaries. Institute of Materials and Strength Physics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 77–82, March, 1998.     

Nature of the temperature dependence of plasticity in the polycrystalline intermetallic compound Ni3Al

The effect of temperature on the plasticity, the type of failure, and the fractions of brittle intercrystallite and viscous transcrystallite failure of the intermetallic compound Ni-24 at. % Al have been studied with boron and without boron. A method is proposed for determining the cohesive strength of the grain boundaries by using the parameters of the flow curve and taking account of the local plastic deformation at the tip of the crack. It is shown that the cohesive strength of the grain boundaries is quite high in Ni₃Al and it is not the cause of the low-temperature embrittlement. The temperature dependence of the plasticity in the Ni-25 at. % Al alloy with boron and without boron in the region of the anomalous temperature dependence of the flow limit is determined by the change in the deformational hardening coefficient and at higher temperatures by a lowering of the cohesive strength of the grain boundaries.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk University. Institute for Strength and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 80–89, November, 1994.     

Dislocation substructure formed by irradiating iron with a low-energy high-current electron beam

Calculations were made of the time variation of the temperature in iron at different depths from a surface irradiated with a low-energy high-current electron beam. The mutual relationship betwen the changes in the dislocation and grain structures of the iron polycrystals and the maximum temperature reached during irradiation was traced. The variation of the microhardness in the surface layers of the irradiated iron was found to be nonmonotonic.V. D. Kuznetsov Siberian Physicotechnical Scientific-Research Institute, Tomsk State University. Institute of Power Electronics, Siberian Branch of the Russian Academy of Sciences. Physics Institute of Strength and Materials Science, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 42–47, May, 1993.     

Microplastic deformation of polycrystals during cyclic loading

A model of microplastic deformation of polycrystals during zero-start cyclic loading with tensions lower than the yield strength is proposed according to which during cycling, thermally activated movement of dislocations occurs under conditions of stress relaxation. Based on this model and the statistical theory of polycrystalline microdeformation, the accumulation of microplastic deformation is theoretically described as a function of the number of loading cycles and the stress amplitudes. It is theoretically proved that in the cycling process the microplastic deformation that accumulates over one cycle decreases as the number of cycles increases; up to the macroscopic elastic limit it is independent of the stress amplitude, and then sharply increases. Agreement of the theory with experimental data for spring alloys is observed in the density of mobile dislocations, which decreases during cycling.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 29–34, March, 1990.     

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.     

Influence of deviation from stoichiometry on the plasticity and mechanism of fracture of the boron-alloyed intermetallic compound Ni3Al obtained by self-propagating high-temperature synthesis

We have studied the effect that deviation of the composition of an ally from stoichiometry has on the plasticity , strength _B, and the fracture mechanism of the intermetallic compound Ni₃Al obtained by self-propagating high-temperature synthesis. The variation of the tensile strength, plasticity, type of fracture, and the cohesive strength _coh of grains have been show to be correlated. The cohesive strength increases with the Al content in the alloy, most rapidly up to 24.0 at. % Al.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 104–110, April, 1994.     

Influence of boron on the low-temperature plasticity and fracture mechanism in the high-temperature synthesis of the intermetallic Ni3Al

We have studied the influence of boron on the plasticity and strength of the intermetallic compound Ni₃Al at stoichiometric and nonstoichiometric compositions, grown by self-propagating high temperature synthesis. We have determined the nature of the fracture and the fraction of brittle intercrystallite and viscous transcrystallite fracture. A correlation is found between the low temperature plasticity and the fraction of transcrystallite fracture. It is shown that the addition of boron, up to its solubility increases the cohesive strength of the grain boundaries in melts at the stoichiometric and nonstoichiometric compositions. In a melt with 25 at. % Al it remains about two times smaller than in a melt with 24 at. % Al.V. D. Kuznetsova Physicotechnical Institute at Tomsk University, Siberia. Institute for the Physics of Strength and Materials Fabrication, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 47–53, December, 1993.     

Transformation of a single-pulse echo into a two-pulse one upon change in excitation pulse form

Physics Institute, Siberian Branch, Russian Academy of Sciences. Applied Physics Problems Scientific-Research Institute, Belorussian University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 1, pp. 96–98, January, 1992.     

Role of packing-defect energy in the localization of plastic strain during shock-wave loading of copper-based solid solutions

The formation of deformation structure accompanying a change in the packing-defect energy (PDE) and the conditions of deformation of copper-based solid solutions under shock-wave loading were investigated by the method of optical microscopy. It is shown that in the case of solid solutions with high PDE plastic strain is localized. This localization increases with the amplitude and duration of the shock pulse, and this in turn gives rise to the generation and growth of microcracks. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 2, pp. 30–34, February, 1993.     

基于GaSe和GaSe0.7S0.3单晶的单脉冲CO2激光倍频器

描述了使用电感储能发生器和半导体转换开关泵浦的工作波长为10.6μm的高效CO2激光器。给出了激光泵浦的非线性晶体GaSe和GaSe0.7S0.3的二次谐波振荡的实验数据和理论估算结果。结果显示,GaSe晶体在输入能量为180mJ时,最大能量转换效率为0.38%,倍频激光的峰值功率为8 kW。     

Deformation processes in tungsten carbide powder ground in a ball mill

Electron diffraction microscopy and x-ray structural analysis are used to study the evolution of particle size and defect structure in tungsten carbide powder during deformation by grinding in a ball mill. Correlations are obtained between grinding time, particle size, and defect structure parameters (scalar dislocation density and azimuthal component of the full disorientation angle).Structural Engineering Institute, Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 62–67, May, 1992.