Local Accommodation Processes of Superplastic Grain Boundary Sliding: Their Direct Observation in Two-Dimensional Grain Boundary Sliding

2018 ◽  
Vol 385 ◽  
pp. 155-160 ◽  
Author(s):  
Eiichi Sato ◽  
Hiroshi Masuda ◽  
Yoshito Sugino ◽  
Shigeharu Ukai
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Surface Effect ◽  
Grain Boundary Sliding ◽  
Grain Structure ◽  
Two Dimensional ◽  
Rate Condition ◽  
Line Spacing ◽  
Strain Rate Condition ◽  
Boundary Sliding

Accommodation processes are crucial for grain boundary sliding in superplasticity though few have been reported on their positive experimental evidences. The present study achieved two-dimensional grain boundary sliding in ODS ferritic steel which had elongated and aligned grain structure and got direct observations of accommodation processes without the surface effect of floating grains: 1) In Region II, diffusional accommodation was confirmed through observing the change in marking-line spacing, which indicates volume inflow and outflow at grain boundaries. 2) Between Regions II and III, dislocation accommodation inside of the mantle region, as proposed by Gifkins, was confirmed through observing curves of marking lines near grain boundaries. 3) In Region III, dislocation accommodation inside of the core region, as proposed by Ball and Hutchison, was confirmed through observing slip bands and sub-boundaries passing through a grain. It is, then, derived that superplasticity relies not on a single mechanism but on several diffusional and dislocation accommodations contributing depending on strain rate condition.

Research on Micro-Mechanism of Nanocomposite Ceramic in Two-Dimensional Ultrasound Grinding

2007 ◽  
Vol 359-360 ◽  
pp. 344-348 ◽  
Author(s):  
Bo Zhao ◽  
Yan Wu ◽  
Guo Fu Gao ◽  
Feng Jiao
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Deformation Mechanism ◽  
Ground Surface ◽  
Grain Boundary Sliding ◽  
Second Phase ◽  
Two Dimensional ◽  
Composite Ceramics ◽  
Nano Composite ◽  
Boundary Sliding

Surface microstructure of nano-composite ceramics prepared by mixed coherence system and machined by two-dimensional ultrasonic precision grinding was researched using TEM, SEM, XRD detector and other equipments. Structure, formation mechanism and characteristic of metamorphic layer of ground surface of nano-composite ceramics were researched. The experiment shows micro deformation mechanism of ceramic material in two-dimensional ultrasound grinding is twin grain boundary and grain-boundary sliding for Al2O3, and it is crystal dislocation of enhanced phase, matrix grain boundary sliding, coordination deformation of intergranular second phase as well as its deformation mechanism for nano-composite ceramics. The fracture surfaces of nano-composite materials with different microscopic structure were observed using TEM and SEM. Research shows that ZrO2 plays an important influence on the generation and expansion of crack, and enhances the strength of grain boundaries. When grain boundaries is rich in the ZrO2 particles, the crack produced in grinding process will be prevented, and the surface with plastic deformation will be smooth. The results shows nanoparticles dispersed in grain boundary prevents crack propagation and makes materials fracture transgranularly which makes the processed surface fine.

Direct Observation of Two-Dimensional Grain Boundary Sliding and Switching in ODS Ferritic Steel

2016 ◽  
Vol 838-839 ◽  
pp. 43-50
Author(s):  
Eiichi Sato ◽  
Hiroshi Masuda ◽  
Yoshito Sugino ◽  
Shigeharu Ukai
Keyword(s):  
Grain Boundary ◽  
Ferritic Steel ◽  
Tensile Deformation ◽  
Grain Boundary Sliding ◽  
Grain Structure ◽  
Two Dimensional ◽  
Kernel Average Misorientation ◽  
Boundary Sliding ◽  
High Temperature Tensile ◽  
Region Ii

High-temperature tensile deformation was performed using an oxide-dispersionstrengthened (ODS) ferritic steel,, which has grain structure largely elongated and aligned in one direction, in the perpendicular direction. In the superplastic region II, two-dimensional grain boundary sliding (GBS) was achieved, in which the material did not shrink in the grain-axis direction and grain-boundary steps appeared only in the surface perpendicular to the grain axis. In this condition, a classical grain switching event was observed. Using kernel average misorientation maps drawn with SEM/EBSD, dominant deformation mechanisms and accommodation processes for GBS were examined in the different regions. Cooperative grain boundary sliding, in which only some of grain boundaries slide, was also observed.

scholarly journals Diffusion-Accommodated Grain Boundary Sliding in a Polycrystal

1990 ◽  
Vol 196 ◽  
Author(s):  
P. M. Hazzledine ◽  
J. H. Schneibel
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Grain Boundary Sliding ◽  
Diffusional Creep ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Material Deposition ◽  
Two Dimensional Model ◽  
Boundary Sliding ◽  
Coble Creep

ABSTRACTA two-dimensional model for diffusional creep (Coble creep) and diffusionaccommodated grain boundary sliding in polycrystals has been developed. The results obtained for small symmetrical clusters of grains reproduce Spingam and Nix's work [Acta Metall. 2M, 1389 (1978)]. For clusters of irregularly shaped grains the material deposition and removal rates, the fluxes along the grain boundaries, the grain boundary tractions as well as the grain boundary sliding rates are irregular and can all be calculated.

Effect of Rare Earth Yttrium on the Hot Ductility of Fe-36Ni Invar Alloy

2014 ◽  
Vol 33 (6) ◽  
pp. 531-537 ◽  
Author(s):  
Y. C. Yu ◽  
H. T. Liu ◽  
W. Q. Chen ◽  
H. G. Zheng
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Testing Temperature ◽  
Grain Boundary Sliding ◽  
Substantial Improvement ◽  
Grain Structure ◽  
Invar Alloy ◽  
Hot Ductility ◽  
Temperature Range ◽  
Boundary Sliding

AbstractThe hot ductility of Fe-36Ni invar alloy doped with and without yttrium was investigated using a Gleeble-3800 thermal-mechanical simulator over the temperature range 850–1050 °C and the improvement mechanism of the hot ductility was analysed with a combination of SEM, EDS and OM. The results showed that Fe-36Ni invar alloy had a poor hot ductility below 1050 °C, which was mainly attributed to the presence of the grain boundary sliding and weak grain boundaries. The addition of 0.048% yttrium had a substantial improvement in the hot ductility of Fe-36Ni invar alloy over the whole testing temperature range especially at 950–1000 °C. At 850–900 °C, the improvement of the hot ductility was mainly associated with the grain boundary strengthening and the restriction of the grain boundary sliding because the addition of yttrium could reduce the segregation of sulfur at grain boundaries and refine the grain structure. At 950–1000 °C, the hot ductility was highly improved, which was owed to the acceleration and occurrence of dynamic recrystallization as a result of the refinement of the grain structure by addition of yttrium.

scholarly journals Hierarchical creep cavity formation in an ultramylonite and implications for phase mixing

Solid Earth ◽  
2017 ◽  
Vol 8 (6) ◽  
pp. 1193-1209 ◽  
Author(s):  
James Gilgannon ◽  
Florian Fusseis ◽  
Luca Menegon ◽  
Klaus Regenauer-Lieb ◽  
Jim Buckman
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Finite Strain ◽  
Grain Boundary Sliding ◽  
Large Strains ◽  
Cavity Formation ◽  
Phase Mixing ◽  
Transient Phenomena ◽  
Boundary Sliding

Abstract. Establishing models for the formation of well-mixed polyphase domains in ultramylonites is difficult because the effects of large strains and thermo-hydro-chemo-mechanical feedbacks can obscure the transient phenomena that may be responsible for domain production. We use scanning electron microscopy and nanotomography to offer critical insights into how the microstructure of a highly deformed quartzo-feldspathic ultramylonite evolved. The dispersal of monomineralic quartz domains in the ultramylonite is interpreted to be the result of the emergence of synkinematic pores, called creep cavities. The cavities can be considered the product of two distinct mechanisms that formed hierarchically: Zener–Stroh cracking and viscous grain-boundary sliding. In initially thick and coherent quartz ribbons deforming by grain-size-insensitive creep, cavities were generated by the Zener–Stroh mechanism on grain boundaries aligned with the YZ plane of finite strain. The opening of creep cavities promoted the ingress of fluids to sites of low stress. The local addition of a fluid lowered the adhesion and cohesion of grain boundaries and promoted viscous grain-boundary sliding. With the increased contribution of viscous grain-boundary sliding, a second population of cavities formed to accommodate strain incompatibilities. Ultimately, the emergence of creep cavities is interpreted to be responsible for the transition of quartz domains from a grain-size-insensitive to a grain-size-sensitive rheology.

scholarly journals Grain Boundary Sliding and Atomic Structures in Alumina Bicrystals with [0001] Symmetric Tilt Grain Boundaries

2002 ◽  
Vol 43 (7) ◽  
pp. 1561-1565 ◽  
Author(s):  
Tsuyoshi Watanabe ◽  
Hidehiro Yoshida ◽  
Yuichi Ikuhara ◽  
Taketo Sakuma ◽  
Hiroyuki Muto ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Grain Boundary Sliding ◽  
Atomic Structures ◽  
Symmetric Tilt ◽  
Boundary Sliding

Research on Surface Microstructures of Nanocomposite Ceramics in Two-Dimensional Ultrasonic Ultraprecision Grinding

2007 ◽  
Vol 364-366 ◽  
pp. 909-913 ◽  
Author(s):  
Bo Zhao ◽  
Jing Lin Tong ◽  
Yan Wu ◽  
Guo Fu Gao
Keyword(s):  
Grain Boundary ◽  
Deformation Mechanism ◽  
Grain Boundary Sliding ◽  
Nano Particles ◽  
Surface Generation ◽  
Second Phase ◽  
Two Dimensional ◽  
Boundary Sliding ◽  
Microscopic Deformation ◽  
Surface Microstructures

Using TEM, SEM and XRD, the surface microstructures of nanocomposite ceramics prepared by heterocoagulation was studied in two-dimensional ultraprecision grinding with ultrasonic assistance. This research was focused on the structure of ground surface degenerating layer, surface generation mechanism and characteristics of nanocomposite ceramic parts. The experimental results showed that the microscopic deformation mechanism of the ordinary Al2O3 parts was grain- boundary twinning and grain-boundary sliding while microscopic deformation mechanism of nanophase ceramic parts was the inner crystal dislocation of strengthened phase with intragranular structure. And its deformation coordination mechanisms were the grain-boundary sliding and coordination deformation of intercrystalline second-phase. The observation on the fracture surfaces of nanocomposite materials with different microscopic structures by TEM and SEM showed that ZrO2 particles had an important effect on the generation and expansion of crack in ceramic parts. The introduction of ZrO2 particles strengthened the interface intensity of grain boundary. If there were rich ZrO2 particles on the grain boundary, the cracks generated during the grinding process would be prevented. Smooth and plastic deformation processing surface was obtained. It was proved further that the nanophase materials behaved transcrystalline fracture due to the nano particles, dispersed in the grain boundary and prevented the expansion of crack. This material’s fracture behavior made favorable surface possible. In the precise grinding of nano materials, the plastic removal mechanism dominated the process. The dislocated depth of the nanocomposite ceramics after grinding was bigger than that of common ceramics, which meant that dislocation increased.

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