Improved creep resistance in anisotropic silicon nitride

2001 ◽  
Vol 16 (8) ◽  
pp. 2182-2185 ◽  
Author(s):  
Naoki Kondo ◽  
Yoshikazu Suzuki ◽  
Manuel E. Brito ◽  
Tatsuki Ohji
Keyword(s):  
Silicon Nitride ◽  
Creep Rate ◽  
Tensile Stress ◽  
Creep Behavior ◽  
Creep Resistance ◽  
Elevated Temperatures ◽  
Tensile Creep ◽  
Grain Alignment ◽  
Remarkable Improvement ◽  
Order Of Magnitude

Tensile creep behavior of silicon nitride with aligned rodlike grains (anisotropic silicon nitride), fabricated by superplastic forging, was investigated at elevated temperatures. Creep rate of the anisotropic silicon nitride was about 1 order of magnitude lower than that of the isotropic one (without forging). The stress sensitivities for the isotropic and anisotropic specimens at 1200 °C were 2.1 and 2.6, respectively, and that for the anisotropic specimen at 1250 °C was 3.6. The grain alignment should cause a remarkable improvement in the creep resistance when a tensile stress is applied along the alignment direction.

Influence of Grain Size on the Tensile Creep Behavior of Ytterbium-Containing Silicon Nitride

2004 ◽  
Vol 87 (3) ◽  
pp. 421-430 ◽  
Author(s):  
Sheldon M. Wiederhorn ◽  
Antonio R. Arellano Lopez ◽  
William E. Luecke ◽  
Michael J. Hoffmann ◽  
Bernard J. Hockey ◽  
...  
Keyword(s):  
Grain Size ◽  
Silicon Nitride ◽  
Creep Behavior ◽  
Tensile Creep

Creep Behavior of Improved High Temperature Silicon Nitride

2005 ◽  
Vol 287 ◽  
pp. 381-392 ◽  
Author(s):  
Sheldon M. Wiederhorn ◽  
Ralph F. Krause ◽  
František Lofaj ◽  
U. Täffner
Keyword(s):  
Silicon Nitride ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Secondary Phase ◽  
Creep Mechanism ◽  
Tensile Creep ◽  
Confidence Limits ◽  
Silicon Nitrides ◽  
Critical Limit ◽  
Consistent Picture

New data are presented on the tensile creep behavior of silicon nitride sintered with Lu2O3. The data are compared with two earlier sets of data collected on the same material. The older sets gave results that are difficult to explain theoretically: a high value for the stress exponent, n=5.33, and no cavitation. The new set of data also gave no cavitation, but gave a stress exponent, n=1.81, that can be rationalized theoretically in terms of solution-precipitation creep of the silicon nitride grains. An analysis of variance showed that one of the earlier sets of data was statistically consistent with the newer set, whereas the other set of data was not. Combining the two sets of data that agreed statistically yields a consistent picture of creep with a low value of the stress exponent and no cavitation. The stress exponent for the combined set of data is n=1.87±0.48 (95 % confidence limits). The tensile creep mechanism of the silicon nitride containing Lu2O3, solution-precipitation, differs from those of other silicon nitrides, for which tensile creep has been attributed to cavitation. Enhancement of the creep resistance of the silicon nitride sintered with Lu2O3 may be a consequence of the fact that Lu2O3 produces a more deformation resistant amorphous phase at the two grain junctions, than do Y2O3 or Yb2O3. In parallel, reducing the amount of secondary phase below a critical limit, or increasing the viscosity of the two grain boundaries relative to three-grain junctions reduces the ability of the material to cavitate during creep, and forces the creep mechanism to change from cavitation to solution-precipitation.

Tensile Creep Behavior in Lutetia-doped Silicon Nitride Ceramics

2005 ◽  
Vol 20 (8) ◽  
pp. 2213-2217 ◽  
Author(s):  
Toshiyuki Nishimura ◽  
Naoto Hirosaki ◽  
Yoshinobu Yamamoto ◽  
Yorinobu Takigawa ◽  
Jian-Wu Cao
Keyword(s):  
Silicon Nitride ◽  
Strain Rate ◽  
Applied Stress ◽  
Creep Behavior ◽  
Stress Rupture ◽  
Tensile Creep ◽  
Time To Failure ◽  
Transmission Electron ◽  
Nitride Ceramics ◽  
Minimum Strain Rate

We studied tensile creep behavior in two silicon nitride ceramics, i.e., 4.8 mol% Lu2O3 (SN48) and 1.2 mol% Lu2O3 (SN12), at 1400–1500 °C under applied stress of 137–300 MPa. Time to failure of SN48 increased with decreasing applied stress and minimum strain rate. The stress–rupture parameter was 10.7 at 1400 °C and 11.4 at 1500 °C. Pore formation was confirmed in a creep-tested specimen of SN48 by transmission electron microscopy. These results suggest that SN48 was fractured by creep rupture. The minimum strain rate of SN12 was almost below the measurement system limitation at temperatures below 1500 °C. Time to failure tended to increase with decreasing applied stress. The stress–rupture parameter was 41 at 1400 °C and 73 at 1500 °C. These results suggest that SN12 was fractured by subcritical crack growth.

Development and Evaluation of Ceramic Components for 8000-kW Class Hybrid Gas Turbine

2001 ◽  
Author(s):  
Sazo Tsuruzono ◽  
Makoto Yoshida ◽  
Toshifumi Kubo ◽  
Takashi Ono ◽  
Takero Fukudome
Keyword(s):  
High Temperature ◽  
Silicon Nitride ◽  
Gas Turbine ◽  
Thermal Efficiency ◽  
Technology Development ◽  
Tensile Creep ◽  
Development Organization ◽  
New Energy ◽  
Ceramic Components

An 8000 kW class hybrid gas turbine (HGT) project, administered by the New Energy and Industrial Technology Development Organization (NEDO) and sponsored by the Ministry of International Trade and Industry (MITI), has been started in July 1999 in Japan[1]. The target of this project is improvement in thermal efficiency and output power by using ceramic components, and earlier commercialization of the gas turbine system. Ceramic components are used for stationary parts subjected to high temperature, such as combustor liners, transition ducts, and first stage turbine nozzles. The gas turbine development was conducted in cooperation with Kawasaki Heavy Industries, Ltd. (KHI). Kyocera started a study on fabricating the ceramic HGT components after evaluating their shape, placement, and fabrication methods. For these ceramic components, we are using the SN282 silicon nitride material developed and used for ceramic gas turbine components in the previous ceramic gas turbine project (300kW CGT)[2-4]. We have started to accumulate the strength evaluation data, using test bars cut from the aforementioned components, and begun long term tensile creep testing to confirm the reliability of the ceramic components.

Reliability of a Conceptual Ceramic Gas Turbine Component Subjected to Static and Transient Thermomechanical Loading

1997 ◽  
Author(s):  
Paul S. DiMascio ◽  
Robert M. Orenstein ◽  
Harindra Rajiyah
Keyword(s):  
Silicon Nitride ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Ceramic Materials ◽  
Combustion Products ◽  
Tensile Creep ◽  
Creep Model ◽  
Gas Combustion ◽  
Component Reliability ◽  
Reliability Models

A three year program to evaluate the feasibility of using monolithic silicon nitride ceramic components in gas turbines was conducted. The use of ceramic materials may enable design of turbine components which operate at higher gas temperatures and/or require less cooling air than their metal counterparts. The feasibility evaluation consisted of three tasks: 1) Expand the material properties database for candidate silicon nitride materials, 2) Demonstrate the ability to predict ceramic reliability and life using a conceptual component model and 3) Evaluate the effect of proof testing on conceptual component reliability. The overall feasibility goal was to determine whether established life and reliability targets could be satisfied for the conceptual ceramic component having properties of an available material. Fast and delayed fracture reliability models were developed and validated via thermal shock and tensile experiments. A creep model was developed using tensile creep data. The effect of oxidation was empirically evaluated using four-point flexure samples exposed to flowing natural gas combustion products. The reliability- and life-limiting failure mechanisms were characterized in terms of temperature, stress and probability of component failure. Conservative limits for design of silicon nitride gas turbine components were established.

Influence of hydrostatic pressure and volumetric strain on the mechanical long term behavior of polymers

2012 ◽  
Vol 32 (6-7) ◽  
pp. 327-333 ◽  
Author(s):  
Tobias Naumann ◽  
Markus Stommel
Keyword(s):  
Hydrostatic Pressure ◽  
Mechanical Behavior ◽  
Free Volume ◽  
Creep Behavior ◽  
Volumetric Strain ◽  
Material Model ◽  
Tensile Creep ◽  
Creep Tests ◽  
Long Term Behavior

Abstract One of the most crucial issues in developing a material model to describe the long term behaviour of polymers is to represent adequately the load dependency of the considered material. In many publications, it is shown that the free volume affects the mechanical behavior of polymers. For a further investigation of the dependency of the creep behavior on free volume, different experiments are presented in this paper. In one experiment, the creep behavior under tension and shear are compared, to see how the different hydrostatic pressures in these tests influence mechanical behavior. Furthermore, tensile creep tests under different hydrostatic pressures are conducted experimentally. The experiments are conducted on a polycarbonate, a polypropylene and a polymethyl methacrylate. It is shown that the hydrostatic pressure has a significant influence on the creep behavior of all three materials. This effect is related to the change of free volume.

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