Orientation-dependent properties of silicon nitride with aligned reinforcing grains

2000 ◽  
Vol 15 (1) ◽  
pp. 130-135 ◽  
Author(s):  
Dong-Soo Park ◽  
Myoung-Je Choi ◽  
Tae-Wook Roh ◽  
Hai-Doo Kim ◽  
Byung-Dong Han
Keyword(s):  
Fracture Toughness ◽  
Silicon Nitride ◽  
Flexural Strength ◽  
Laminate Composite ◽  
Tape Casting ◽  
Sintered Sample ◽  
Propagation Direction ◽  
Point Of View ◽  
Crack Propagation Direction ◽  
Gas Pressure Sintering

Silicon nitride with the aligned reinforcing grains was prepared by tape casting with addition of the silicon nitride whiskers and gas-pressure sintering at 2148 K. The microstructure and the mechanical properties of the sintered sample, including the fracture toughness and the three-point flexural strength, were highly anisotropic. Both the fracture toughness and the flexural strength were the highest when the crack-propagation direction was normal to the alignment direction. This result was interpreted from the laminate composite materials’ point of view. Although the large elongated grains were as long as 44.4 ± 12 μm and as wide as 5.1 ± 0.67 μm, they were not the fracture origins.

Microstructure and Properties of Sintered Reaction Bonded Silicon Nitride with Aligned Whisker Seeds

2005 ◽  
Vol 287 ◽  
pp. 271-276
Author(s):  
Dong Soo Park ◽  
Byung Dong Hahn ◽  
D.-J. Baik
Keyword(s):  
Fracture Toughness ◽  
Phase Transformation ◽  
Silicon Nitride ◽  
Flexural Strength ◽  
Tape Casting ◽  
Gas Pressure ◽  
The Other ◽  
Sintering Additives ◽  
Si3n4 Whisker ◽  
Gas Pressure Sintering

Sintered reaction bonded silicon nitride with aligned whisker seeds was prepared by tape casting silicon slurry with 5 wt% b-Si3N4 whisker seeds followed by nitridation and sintering. Three different sintering additives were used for the samples; 7 wt% Y2O3, 6 wt% Y2O3 + 1 wt% Al2O3 and 5 wt% Y2O3 + 2 wt% Al2O3. The sample with 5 wt% Y2O3 + 2 wt% Al2O3 showed the fastest a to b phase transformation after nitridation and the highest fracture toughness and flexural strength after gas pressure sintering among the samples. It also had finer microstructure than the other samples after sintering at 2248 K and at 2273 K. The finer microstructure was related to the faster phase transformation after nitridation, which resulted in the higher flexural strength.

Effects of Sintering Additives on the Microstructure and Mechanical Properties of Silicon Nitride Ceramics by GPS

2010 ◽  
Vol 105-106 ◽  
pp. 27-30 ◽  
Author(s):  
Wei Ru Zhang ◽  
Feng Sun ◽  
Ting Yan Tian ◽  
Xiang Hong Teng ◽  
Min Chao Ru ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Phase Transformation ◽  
Silicon Nitride ◽  
Porous Silicon ◽  
Flexural Strength ◽  
Relative Density ◽  
Sintering Additives ◽  
Microstructure And Mechanical Properties ◽  
Nitride Ceramics

Silicon nitride ceramics were prepared by gas pressure sintering (GPS) with different sintering additives, including La2O3, Sm2O3 and Al2O3. Effect of sintering additives on the phase-transformation, microstructure and mechanical properties of porous silicon nitride ceramics was investigated. The results show that the reaction of sintering additives each other and with SiO2 had key effects on the phase-transformation, grain growing and grain boundaries. With 9MPa N2 atmosphere pressure, holding 1h at 1850°C, adding 10wt% one of the La2O3, Sm2O3, Al2O3, porous silicon nitride was prepared and the relative density was 78%, 72%, 85% respectively. The flexural strength was less than 500MPa, and the fracture toughness was less than 4.8MPam1/2. Dropping compounds sintering additives, such as La2O3+Al2O3, Sm2O3+Al2O3 effectively improves the sintering and mechanical properties. The relative density was 99.2% and 98.7% with 10wt% compounds sintering additives. The grain ratio of length to diameter was up to 1:8. The flexural strength was more than 900MPa, and the fracture toughness was more than 8.9MPam1/2.

Thermal Conductivity of Si₃N₄ Ceramics Fabricated From Carbothermal-reduction-derived Powder

2021 ◽  
Author(s):  
Yuelong Wang ◽  
Xingyu Li ◽  
Haoyang Wu ◽  
Baorui Jia ◽  
Deyin Zhang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Fracture Toughness ◽  
Grain Size ◽  
Flexural Strength ◽  
Grain Boundaries ◽  
Carbothermal Reduction ◽  
Secondary Phase ◽  
Gas Pressure ◽  
Gas Pressure Sintering

Abstract Si3N4-based ceramic (Si3N4-5wt%Y2O3-3wt%MgO) was obtained from carbothermal-reduction-derived powder combined with gas pressure sintering. The phase, microstructure, thermal conductivity and mechanical properties of Si3N4 ceramics were comprehensively analyzed. Dense Si3N4 ceramic with uniform grain size was obtained after sintering at 1900°C for 7 h under a N2 pressure of 1.2 MPa. The secondary phase consisted of Y4Si2O7N2 and Y2Si3O3N4 was found to gather around triangular grain boundaries. The thermal conductivity, flexural strength, hardness and fracture toughness of the Si3N4 ceramics were 95.7 W·m-1·k-1, 715 MPa, 17.2 GPa and 7.2 MPa·m1/2, respectively. The results were compared with product derived from commercial powder, the improvement of thermal conductivity (~8.3%) and fracture toughness (~4.3%) demonstrating the superiority of Si3N4 ceramics prepared from carbothermal-reduction-derived powder.

Effect of Molding Process on Properties of Laminated ZrB2-SiC-Cg Ultra High Temperature Ceramics

2014 ◽  
Vol 602-603 ◽  
pp. 443-446
Author(s):  
Chun Cheng Wei ◽  
Xing Hong Zhang ◽  
Wen Bo Han ◽  
Ping Hu
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Flexural Strength ◽  
Fracture Behavior ◽  
Tape Casting ◽  
Molding Process ◽  
Ultra High Temperature Ceramics ◽  
Matrix Layer ◽  
Properties Of Materials ◽  
Fracture Work

Laminated ZrB2-SiC-Cg ceramics were successfully prepared by tape casting - dipping and tape casting - stacking respectively. The effect of different molding process on the mechanical properties of materials was investigated. The microstructure and fracture behavior were characterized as well. The flexural strength, fracture toughness and fracture work of laminated ZrB2-SiC-Cg ceramics prepared by tape casting-stacking were 427 MPa, 11.3 MPa·m1/2, 415 J/m2, respectively. The thickness of ZrB2-SiC layers was about 250 μm, and the thickness of graphite layers was about 25 μm. As a comparison, Laminated ZrB2-SiC-Cg ceramics prepared by tape casting - dipping showed non-uniform thickness of the ZrB2-SiC layers and graphite layers. And the flexural strength, fracture toughness and fracture work of laminated ZrB2-SiC-Cg ceramics prepared by tape casting-dipping were 252 MPa, 5.7 MPa·m1/2, 104 J/m2, respectively. The improvement on the mechanical properties of laminated ZrB2-SiC-Cg ceramics prepared by tape casting - stacking was attributed to the uniform graphite layer and ZrB2-SiC layer and the reducing amount of graphite infiltrated into ZrB2-SiC matrix layer.

Microstructural Evolution and Mechanical Properties in Yb2O3–Fluxed Silicon Nitride Ceramics

2007 ◽  
Vol 336-338 ◽  
pp. 1172-1174
Author(s):  
Gang Feng Guo ◽  
Xiao Zhan Yang ◽  
Jian Bao Li ◽  
Hong Lin ◽  
Long Liang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Silicon Nitride ◽  
Flexural Strength ◽  
Microstructural Evolution ◽  
Intergranular Fracture ◽  
Fracture Mode ◽  
Transgranular Fracture ◽  
Sintering Additive ◽  
Nitride Ceramics

Silicon nitride ceramics were fabricated with Yb2O3 as the sintering additive. The effects of the amount of Yb2O3 on the microstructure and the mechanical properties such as the flexural strength and the fracture toughness were investigated. Almost fully densified Si3N4 was obtained when only 4 wt% Yb2O3 was added. Both the flexural strength and the fracture toughness increased steadily with the Yb2O3 content. The transgranular fracture mode was observed in the specimen containing 4 wt% Yb2O3, however, the intergranular fracture mode was observed in the specimen containing 10 wt% Yb2O3.

Effect of β–Si3N4 seed crystal on the microstructure and mechanical properties of sintered reaction-bonded silicon nitride

1999 ◽  
Vol 14 (1) ◽  
pp. 178-184 ◽  
Author(s):  
Soo Young Lee ◽  
K. Amoako-Appiagyei ◽  
Hai Doo Kim
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Silicon Nitride ◽  
High Strength ◽  
Considerable Improvement ◽  
Seed Crystal ◽  
Bimodal Microstructure ◽  
Seed Crystals ◽  
Before And After ◽  
Gas Pressure Sintering

β–Si3N4 seed crystal has been synthesized from α–Si3N4 powder. Reaction-bonded Si3N4/SiC composite has been fabricated with β–Si3N4 seed crystals. The nitridation behavior and the changes in mechanical properties resulting from the addition of seed crystals were studied before and after gas pressure sintering. Addition of seeds showed a considerable improvement in the nitridation, resulting in increase in fracture strength of the composite. Highly nitrided reaction-bonded Si3N4 (RBSN) as a result of the addition of seed crystals gave rise to high strength of composite after postsintering. Fracture toughness of the seeded Si3N4 was also improved up to 35% compared to the baseline Si3N4. Micrographs showed that the seeded Si3N4 developed a bimodal microstructure which resulted in an improvement in fracture toughness.

On Fatigue Crack Propagation of One-Way Rail Road

2006 ◽  
Vol 326-328 ◽  
pp. 971-974
Author(s):  
Khalil Farhangdoost ◽  
Mohammad Kavoosi
Keyword(s):  
Fracture Toughness ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Initial Crack ◽  
Propagation Direction ◽  
Hydraulic Pressure ◽  
Stress Intensity Range ◽  
Crack Propagation Direction ◽  
Crack Angle

In this paper, the mechanism of fatigue crack propagation of one-way rail road and the effects of some parameters such as crack length, initial crack angle, contact stress, friction, hydraulic pressure and crack propagation direction, in fracture toughness are presented so that it can be used to predict the fatigue life of rail road. The results of stress intensity range factor in one-way rail road are compared with two-way rail road. It is demonstrated that the crack in one-way growth faster than two-way rail road.

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