scholarly journals Анализ условий зарождения зернограничных нанопор в субмикрокристаллических материалах в процессе интенсивной пластической деформации

2020 ◽  
Vol 46 (19) ◽  
pp. 25
Author(s):  
В.Н. Перевезенцев ◽  
А.C. Пупынин
Keyword(s):  
Plastic Deformation ◽  
Hydrostatic Pressure ◽  
Grain Boundary ◽  
Internal Stress ◽  
Nucleation Rate ◽  
Stress Fields ◽  
External Hydrostatic Pressure ◽  
Submicrocrystalline Materials

A model decribed the nucleation of grain boundary nanopores in submicrocrystalline materials in the process of intensive plastic deformation is proposed. The effect of internal stress fields from planar mesodefects, external hydrostatic pressure and level of supersaturation of the material by nonequilibrium deformation-induced vacancies on the nucleation rate of nanopores is analyzed.

scholarly journals DIFFUSION NUCLEATION OF CAVITIES IN GRAIN JUNCTIONS OF SUBMICROCRYSTALLINE MATERIALS

2021 ◽  
Vol 83 (3) ◽  
pp. 276-284
Author(s):  
A.S. Pupynin ◽  
S.V. Kirikov ◽  
V.N. Perevezentsev
Keyword(s):  
Plastic Deformation ◽  
Hydrostatic Pressure ◽  
High Pressure Torsion ◽  
Vacancy Concentration ◽  
Triple Junctions ◽  
External Hydrostatic Pressure ◽  
Tensile Stresses ◽  
Boundary Triple ◽  
Junction Disclinations ◽  
Submicrocrystalline Materials

The conditions of diffusional cavity nucleation in submicrocrystalline materials processed by the methods of intensive plastic deformation (equal-channel angular pressing, multiaxial forging, high pressure torsion, etc.) are analyzed. To date, the question of the mechanism of nucleation of cavities in such materials remains debatable due to the fact that the processing of materials by the methods of intensive plastic deformation is carried out at high hydrostatic pressures that prevent the appearance of pores. The possibility of diffusive nucleation of nanopores in the region of triple junctions of grains containing negative strain-induced wedge disclinations, generating high tensile stresses in the vicinity of triple junctions, comparable in magnitude to external hydrostatic pressure, is shown. Such junction disclinations inevitably occur at the grain junctions due to the heterogeneity of the plastic deformation through the ensemble of polycrystal grains. It is shown that an important condition for the nucleation of cavities is not only the presence of high internal tensile stresses from junction disclinations, but also an extremely high concentration of nonequilibrium strain-induced vacancies characteristic of submicrocrystalline metals, comparable in values to the vacancy concentration, at temperatures close to solidus. The influence of the strength of junction disclinations, the value of external hydrostatic pressure and the degree of supersaturation of the material by nonequilibriumstrain-induced vacancies on the rate of diffusional nucleation and the volume of critical pore nuclei is analyzed. It is established that in order to effectively suppress the process of pore formation in the grain boundary triple junctions, it is necessary to apply an external hydrostatic pressure that compensates for internal elastic fields from junction disclinations.

The Effect of Grain Boundary State on Deformation Process Development in Nanostructured Metals Produced by the Methods of Severe Plastic Deformation

2011 ◽  
Vol 683 ◽  
pp. 69-79 ◽  
Author(s):  
Evgeny V. Naydenkin ◽  
Galina P. Grabovetskaya ◽  
Konstantin Ivanov
Keyword(s):  
Plastic Deformation ◽  
Grain Boundary ◽  
Severe Plastic Deformation ◽  
Deformation Process ◽  
Process Development ◽  
Grain Boundary Sliding ◽  
Total Deformation ◽  
Nanostructured Metals ◽  
Boundary State ◽  
Boundary Sliding

In this review the investigations of deformation process development are discussed which were carried out by tension and creep in the temperature range Т<0.4Tm (here Тm is the absolute melting point of material) for nanostructured metals produced by the methods of severe plastic deformation. The contribution of grain boundary sliding to the total deformation in the above temperature interval is also considered. An analysis is made of the effect of grain size and grain boundary state on the evolution of grain boundary sliding and cooperative grain boundary sliding in nanostructured metals.

scholarly journals Grain Boundary Segregation in UFG Alloys Processed by Severe Plastic Deformation

2012 ◽  
Vol 14 (11) ◽  
pp. 968-974 ◽  
Author(s):  
Xavier Sauvage ◽  
Artur Ganeev ◽  
Yulia Ivanisenko ◽  
Nariman Enikeev ◽  
Maxim Murashkin ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Grain Boundary ◽  
Severe Plastic Deformation ◽  
Boundary Segregation ◽  
Grain Boundary Segregation

Study of Ductile-to-Brittle Transition in Single Grit Diamond Scribing of Silicon: Application to Wire Sawing of Silicon Wafers

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Hao Wu ◽  
Shreyes N. Melkote
Keyword(s):  
Hydrostatic Pressure ◽  
Silicon Wafers ◽  
Depth Of Cut ◽  
Critical Depth ◽  
External Hydrostatic Pressure ◽  
Tensile Stresses ◽  
Brittle Transition ◽  
Ductile Mode Cutting ◽  
Critical Depth Of Cut ◽  
Ductile To Brittle Transition

The ductile-to-brittle cutting mode transition in single grit diamond scribing of monocrystalline silicon is investigated in this paper. Specifically, the effects of scriber tip geometry, coefficient of friction, and external hydrostatic pressure on the critical depth of cut associated with ductile-to-brittle transition and crack generation are studied via an eXtended Finite Element Method (XFEM) based model, which is experimentally validated. Scribers with a large tip radius are shown to produce lower tensile stresses and a larger critical depth of cut compared with scribers with a sharp tip. Spherical tipped scribers are shown to generate only surface cracks, while sharp tipped scribers (conical, Berkovich and Vickers) are found to create large subsurface tensile stresses, which can lead to nucleation of subsurface median/lateral cracks. Lowering the friction coefficient tends to increase the critical depth of cut and hence the extent of ductile mode cutting. The results also show that larger critical depth of cut can be obtained under external hydrostatic pressure. This knowledge is expected to be useful in optimizing the design and application of the diamond coated wire employed in fixed abrasive diamond wire sawing of photovoltaic silicon wafers.

Modern Models of Grain Boundary Diffusion

2011 ◽  
Vol 312-315 ◽  
pp. 1116-1125
Author(s):  
Vladimir V. Popov
Keyword(s):  
Plastic Deformation ◽  
Grain Boundary ◽  
Severe Plastic Deformation ◽  
Nanocrystalline Materials ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Coarse Grained ◽  
Gas Condensation ◽  
Non Equilibrium

Recent models of grain-boundary diffusion are briefly reviewed. Models of diffusion along equilibrium boundaries of recrystallization origin in coarse-grained materials and along non-equilibrium boundaries in nanocrystalline materials obtained by gas condensation and compacting or by severe plastic deformation are considered separately.

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