Impression Creep Behavior of Atmospheric Plasma-Sprayed and Hot Pressed MoSi2/Si3N4

1997 ◽  
Author(s):  
K.J. Hollis ◽  
D.P. Butt ◽  
R.G. Castro
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Creep Behavior ◽  
Grain Boundary Sliding ◽  
Atmospheric Plasma ◽  
Second Phase ◽  
Impression Creep ◽  
Creep Mechanisms ◽  
Boundary Sliding ◽  
Plasma Sprayed

Abstract The use of MoSi2 as a high temperature oxidation resistant structural material is hindered by its poor elevated temperature creep resistance. The addition of second phase Si3N4 holds promise for improving the creep properties of MoSi2 without decreasing oxidation resistance. The high temperature impression creep behavior of atmospheric plasma sprayed (APS) and hot pressed (HP) MoSi2/Si3N4 composites was investigated. Values for steady state creep rates, creep activation energies, and creep stress exponents were measured. Grain boundary sliding and splat sliding were found to be the dominant creep mechanisms for the APS samples while grain boundary sliding and plastic deformation were found to be the dominant creep mechanisms for the HP samples.

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.

Grain boundary sliding at high temperature deformation in cold-rolled ODS ferritic steels

2014 ◽  
Vol 452 (1-3) ◽  
pp. 628-632 ◽  
Author(s):  
Yoshito Sugino ◽  
Shigeharu Ukai ◽  
Bin Leng ◽  
Naoko Oono ◽  
Shigenari Hayashi ◽  
...  
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Grain Boundary Sliding ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Ferritic Steels ◽  
Boundary Sliding ◽  
Cold Rolled

High-temperature grain boundary sliding behavior and grain boundary energy in cubic zirconia bicrystals

2004 ◽  
Vol 52 (8) ◽  
pp. 2349-2357 ◽  
Author(s):  
Hidehiro Yoshida ◽  
Kenji Yokoyama ◽  
Naoya Shibata ◽  
Yuichi Ikuhara ◽  
Taketo Sakuma
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Boundary Energy ◽  
Grain Boundary Sliding ◽  
Grain Boundary Energy ◽  
Cubic Zirconia ◽  
Boundary Sliding

Evaluation of Plastic Workability Limit of Magnesium Alloy by Cavitations in High Temperature Uni and Biaxial Test

2012 ◽  
Vol 735 ◽  
pp. 67-72
Author(s):  
Kunio Funami ◽  
Daisuke Yamashita ◽  
Kohji Suzuki ◽  
Masafumi Noda
Keyword(s):  
Fine Structure ◽  
High Temperature ◽  
Magnesium Alloy ◽  
Grain Boundary ◽  
Room Temperature ◽  
Grain Boundary Sliding ◽  
Az31 Magnesium Alloy ◽  
Temperature Deformation ◽  
Alloy Plate ◽  
Boundary Sliding

Abstract. This study examined the critical plastic formability limit of a fine-structure AZ31 magnesium alloy plate under warm and high temperature based on the strength of a magnesium alloy that has cavities at room temperature. The cyclic hot free-forging process as pre-form working following rolling at a light reduction ratio fabricated a fine-structure AZ31 magnesium alloy plate. The appearance of the cavities was examined in detail together with changes in the structure and preparation methods before further damage at high temperatures with increasing uni-and biaxial plastic deformation. The allowable deformation limit in the super plasticity process can be estimated from the strength of the deformed material and forming limit diagram (FLD) at room temperature. During high-temperature deformation, cavities are produced by stress concentrations at grain boundary triple points and striation bands due to grain boundary sliding. The cavitations growth behavior is dependent upon deformation conditions, and a high percentage of large cavities occupy the sample surface as a large amount of grain boundary sliding is present, i.e., as uniform elongation grows larger, the cavity size also increases. In a case where 200% uniaxial strain was applied to a fine-grained structure material at a temperature of 623K under a strain rate of 10-4s-1, the tensile strength at room temperature decreased about 13%, and elongation was 10% less, compared with that of a material to which no load was applied due to the influence of cavities. In a case of biaxial deformation, the values were 28% lower. It is possible to draw a FLD based on the cavity incidence fraction .

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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