Analysis of Conditions for the Nucleation of Grain Boundary Nanopores in Submicrocrystalline Materials under Intensive Plastic Deformation

2020 ◽  
Vol 46 (10) ◽  
pp. 964-967
Author(s):  
V. N. Perevezentsev ◽  
A. S. Pupynin
Author(s):  
В.Н. Перевезенцев ◽  
А.C. Пупынин

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.


2011 ◽  
Vol 683 ◽  
pp. 69-79 ◽  
Author(s):  
Evgeny V. Naydenkin ◽  
Galina P. Grabovetskaya ◽  
Konstantin Ivanov

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.


2012 ◽  
Vol 14 (11) ◽  
pp. 968-974 ◽  
Author(s):  
Xavier Sauvage ◽  
Artur Ganeev ◽  
Yulia Ivanisenko ◽  
Nariman Enikeev ◽  
Maxim Murashkin ◽  
...  

2011 ◽  
Vol 312-315 ◽  
pp. 1116-1125
Author(s):  
Vladimir V. Popov

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.


2018 ◽  
Vol 59 (5) ◽  
pp. 822-828
Author(s):  
Wen Long Zhao ◽  
Dong Po Wang ◽  
Hua Dong Wang ◽  
Shi Cheng Ma ◽  
Yu Yi Wang ◽  
...  

1991 ◽  
Vol 238 ◽  
Author(s):  
Douglas E. Meyers ◽  
Alan J. Ardell

ABSTRACTThe results of our initial efforts at measuring the fracture strengths of grain boundaries In Ni3Al using a miniaturized disk-bend test are presented. The samples tested were 3 mm in diameter and between 150 and 300 μm thick. An Ingot of directlonally-solidlfled, boron-free Ni3Al containing 24% Al was annealed between 1300 and 1350 °C to induce grain growth, producing many grain boundaries In excess of 1.5 mm in length. Specimens were cut from these In such a way that one long grain boundary was located near a diameter of the specimen. The relative orientations of the grains on either side of the boundary were determined from electron channeling patterns. Low-angle boundaries are so strong they do not fracture; Instead the samples deform In a completely ductile manner. High-angle boundaries always fracture, but only after considerable plastic deformation of the two grains flanking them. Fracture is Indicated by a load drop in the load vs. displacement curves. A method involving extrapolation of the elastic portion of these curves to the displacement at fracture is used to estimate the fracture stresses. This procedure yields consistent values of the fracture strengths of high-angle boundaries. The measured stresses are large (∼2 to 3 GPa), but considerably smaller than those required for the fracture of special boundaries, as predicted by computer simulations. No correlation was found between the fracture stresses or loads and the geometry of the high-angle boundaries, many of which are close to, but deviate from, coincident site lattice orientations.


Author(s):  
Ryo Kikuchi ◽  
Shujiro Suzuki ◽  
Ken Suzuki

Abstract Ni-based superalloys with excellent high temperature strength have been used in advanced thermal power plants. It was found that grain boundary cracking is caused in the alloy under creep-fatigue loading due to the degradation of the crystallinity of grain boundaries and the grain boundary cracking degrades the lifetime of the alloy drastically. In order to clarify the mechanism of intergranular cracking, in this research, static and dynamic strains were applied to a bicrystal structure of the alloy perpendicularly to the grain boundary using molecular dynamics analysis. In addition, the effect of the accumulation of vacancies in the area with high-density of dislocations on the strength of the bicrystal structure was analysed. It was found that the fracture mode of the bicrystal structure changed from ductile transgranular fracture to brittle intergranular one as strong functions of the combination of Schmid factor of the two grains and the density of defects around the grain boundary. The local heavy plastic deformation occurred around the grain boundary with large difference in Schmid factor between nearby grains and the diffusion of the newly grown dislocations and vacancies was suppressed by the large strain field due to the large mismatch of the crystallographic orientation between the grains. The accumulation of vacancies accelerated the local plastic deformation around the grain boundary. Therefore, the mechanism of the acceleration of intergranular cracking under creep-fatigue loading was successfully clarified by MD analysis.


Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1533
Author(s):  
Haichao Zhang ◽  
Xufeng Wang ◽  
Huirong Li ◽  
Changqing Li ◽  
Yungang Li

The molecular dynamics (MD) method was used to simulate and calculate the segregation energy and cohesive energy of Cu atoms at the Σ3{111}(110) and Σ3{112}(110) grain boundaries, and the tensile properties of the BCC-Fe crystal, with the grain boundaries containing coherent Cu clusters of different sizes (a diameter of 10 Å, 15 Å and 20 Å). The results showed that Cu atoms will spontaneously segregate towards the grain boundaries and tend to exist in the form of large-sized, low-density Cu clusters at the grain boundaries. When Cu cluster exists at the Σ3{111}(110) grain boundary, the increase in the size of the Cu cluster leads to an increase in the probability of vacancy formation inside the Cu cluster during the tensile process, weakening the breaking strength of the crystal. When the Cu cluster exists at the Σ3{112}(110) grain boundary, the Cu cluster with a diameter of 10 Å will reduce the strain hardening strength of the crystal, but the plastic deformation ability of the crystal will not be affected, and the existence of Cu clusters with a diameter of 15 Å and 20 Å will suppress the structural phase transformation of the crystal, and significantly decrease the plastic deformation ability of the crystal, thereby resulting in embrittlement of the crystal.


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