Stacking faults in deformed α-silicon nitride single crystals

1993 ◽  
Vol 51 ◽  
pp. 916-917
Author(s):  
H. Suematsu ◽  
J. J. Petrovic ◽  
T. E. Mitchell
Keyword(s):  
High Temperature ◽  
Silicon Nitride ◽  
Single Crystals ◽  
Stacking Faults ◽  
High Strength ◽  
Secondary Phase ◽  
High Resolution Electron Microscopy ◽  
Diffusional Creep ◽  
Dislocation Slip ◽  
High Temperature Strength

Silicon nitride(Si3N4) is well known for its high toughness and strength. This is the reason why it is selected for ceramic turbo charger rotors in automobile engines. However, the high strength of most sintered Si3N4 products drops above 1200°C because sintering aids like Y2O3 and MgO are required which form glassy phases with low melting points on the grain boundaries. This secondary phase degrades the high temperature characteristics of Si3N4. In order to overcome this deficiency, much work has been reported which aims at crystallizing or removing the glassy phase. If this aim could be successful, resulting in an increase in high temperature strength, other processes would determine the high temperature performance of Si3N4, such as diffusional creep and dislocation slip. Line and planar defects in Si3N4 play an important role in such the processes particularly in slip, however, available knowledge about them is limited. In the present work, stacking faults in deformed Si3N4 single crystals are investigated using high resolution electron microscopy(HREM).

High temperature strength of silicon nitride ceramics with ytterbium silicon oxynitride

1997 ◽  
Vol 12 (1) ◽  
pp. 203-209 ◽  
Author(s):  
Toshiyuki Nishimura ◽  
Mamoru Mitomo ◽  
Hisayuki Suematsu
Keyword(s):  
High Temperature ◽  
Silicon Nitride ◽  
Bending Strength ◽  
High Strength ◽  
Secondary Phase ◽  
Silicon Oxynitride ◽  
High Temperature Strength ◽  
High Melting Point ◽  
Powder Mixtures ◽  
Nitride Ceramics

Silicon nitride ceramics with ytterbium silicon oxynitride (Yb4Si2O7N2) as secondary phase were fabricated by hot-pressing the powder mixtures, including 50.0 to 97.0 mol% of silicon nitride with a mixture of Yb2O3 and SiO2 (Yb2O3/SiO2 = 4). Sinterability of the materials with Yb2O3 was higher than that with Y2O3 in the same composition of raw powder mixtures. High density materials were obtained under the condition of 50.0 to 89.1 mol% of silicon nitride in raw powder mixtures. Mechanical properties of silicon nitride containing 97.6 mol% of Si3N4 and 2.4 mol% of Yb4Si2O7N2 were measured. Fracture toughness measured by the indentation technique was 5.9 MPam1/2. Bending strength at room temperature and at 1500 °C was 977 MPa and 484 MPa, respectively. The silicon nitride grains consisted of highly elongated rod-like grains and thin needle-like grains. The Yb4Si2O7N2 grains were crystallized at multigrain junctions and bonded close to Si3N4 grains. High strength at high temperature is supposed to be based on the presence of crystalline Yb4Si2O7N2 having a high melting point.

Dislocation loops in α-silicon nitride single crystals

1992 ◽  
Vol 50 (1) ◽  
pp. 342-343
Author(s):  
H. Suematsu ◽  
J. J. Petrovic ◽  
T. E. Mitchell
Keyword(s):  
High Temperature ◽  
Silicon Nitride ◽  
Single Crystals ◽  
Mass Production ◽  
High Strength ◽  
Deformation Characteristics ◽  
Dislocation Loops ◽  
Production Lines ◽  
Compressor Rotor ◽  
Structural Applications

Silicon nitride(Si3N4) is well known to be a most promising ceramic material for high temperature structural applications. It has high strength even at 1200°C and its fracture toughness is about 5 to 7 MPa•m½. Si3N4 has been manufactured on mass production lines as the compressor rotor for turbo chargers. For high temperature use, it is important to know the deformation characteristics of the material and the role played by dislocations and other defects. However, research on the nature of defects in Si3N4 has been limited considering the importance of Si3N4. In this study, we have examined defects in single crystals of Si3N4.

Lattice Imaging of Grain Boundaries in Ceramics

1977 ◽  
Vol 35 ◽  
pp. 114-115
Author(s):  
D. R. Clarke ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundaries ◽  
High Temperature Strength ◽  
Current Interest ◽  
Lattice Imaging ◽  
Special Significance ◽  
Structural Applications ◽  
Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

Electron Microscopy of Silicon Nitride-Based Ceramics

1991 ◽  
Vol 49 ◽  
pp. 926-927
Author(s):  
Gareth Thomas
Keyword(s):  
Electron Microscopy ◽  
High Temperature ◽  
Silicon Nitride ◽  
World Wide ◽  
Sintering Temperature ◽  
Liquid Phase Sintering ◽  
High Temperature Strength ◽  
Sintering Additives ◽  
Glass Forming ◽  
Dense Product

Silicon nitride and silicon nitride based-ceramics are now well known for their potential as hightemperature structural materials, e.g. in engines. However, as is the case for many ceramics, in order to produce a dense product, sintering additives are utilized which allow liquid-phase sintering to occur; but upon cooling from the sintering temperature residual intergranular phases are formed which can be deleterious to high-temperature strength and oxidation resistance, especially if these phases are nonviscous glasses. Many oxide sintering additives have been utilized in processing attempts world-wide to produce dense creep resistant components using Si3N4 but the problem of controlling intergranular phases requires an understanding of the glass forming and subsequent glass-crystalline transformations that can occur at the grain boundaries.

Precipitation of NiHfsi phase in NiAl single crystals containing Hf

1995 ◽  
Vol 53 ◽  
pp. 532-533
Author(s):  
A. Garg ◽  
R. D. Noebe ◽  
R. Darolia
Keyword(s):  
High Temperature ◽  
Single Crystals ◽  
High Temperature Strength ◽  
Bridgman Technique ◽  
Shell Mold ◽  
Third Phase ◽  
Unknown Phase ◽  
Transmission Electron ◽  
Two Phases ◽  
Nial Matrix

Small additions of Hf to NiAl produce a significant increase in the high-temperature strength of single crystals. Hf has a very limited solubility in NiAl and in the presence of Si, results in a high density of G-phase (Ni16Hf6Si7) cuboidal precipitates and some G-platelets in a NiAl matrix. These precipitates have a F.C.C structure and nucleate on {100}NiAl planes with almost perfect coherency and a cube-on-cube orientation-relationship (O.R.). However, G-phase is metastable and after prolonged aging at high temperature dissolves at the expense of a more stable Heusler (β'-Ni2AlHf) phase. In addition to these two phases, a third phase was shown to be present in a NiAl-0.3at. % Hf alloy, but was not previously identified (Fig. 4 of ref. 2 ). In this work, we report the morphology, crystal-structure, O.R., and stability of this unknown phase, which were determined using conventional and analytical transmission electron microscopy (TEM).Single crystals of NiAl containing 0.5at. % Hf were grown by a Bridgman technique. Chemical analysis indicated that these crystals also contained Si, which was not an intentional alloying addition but was picked up from the shell mold during directional solidification.

Development and Fabrication of Silicon Nitride Components for Ceramic Gas Turbine

1997 ◽  
Author(s):  
Keisuke Makino ◽  
Ken-Ichi Mizuno ◽  
Toru Shimamori
Keyword(s):  
High Temperature ◽  
Silicon Nitride ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Turbine Blades ◽  
High Strength ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Spark Plug ◽  
Power Turbine

NGK Spark Plug Co., Ltd. has been developing various silicon nitride materials, and the technology for fabricating components for ceramic gas turbines (CGT) using theses materials. We are supplying silicon nitride material components for the project to develop 300 kW class CGT for co-generation in Japan. EC-152 was developed for components that require high strength at high temperature, such as turbine blades and turbine nozzles. In order to adapt the increasing of the turbine inlet temperature (TIT) up to 1,350 °C in accordance with the project goals, we developed two silicon nitride materials with further unproved properties: ST-1 and ST-2. ST-1 has a higher strength than EC-152 and is suitable for first stage turbine blades and power turbine blades. ST-2 has higher oxidation resistance than EC-152 and is suitable for power turbine nozzles. In this paper, we report on the properties of these materials, and present the results of evaluations of these materials when they are actually used for CGT components such as first stage turbine blades and power turbine nozzles.

Evaluation of Multicomponent Nickel Base LI2 and Other Intermetallic Alloys as High Temperature Structural Materials

1986 ◽  
Vol 81 ◽  
Author(s):  
D. M. Shah ◽  
D. N. Duhl
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Single Crystals ◽  
Impact Resistance ◽  
High Strength ◽  
Structural Materials ◽  
Nickel Base Superalloy ◽  
Intermetallic Alloys ◽  
Nickel Base ◽  
Base Superalloy

AbstractMulticomponent nickel base intermetallics with the L12 structure were evaluated as high temperature structural materials. The compounds were based on the γ' composition of PWA 1480, a high strength single crystal nickel base superalloy. The best balance of properties in the compound was achieved with <111> oriented single crystals but no significant advantage could be demonstrated over the precipitation hardened superalloys. Insufficient impact resistance was a major deficiency of the L12 compounds. Other nickel base intermetallics were also evaluated but showed little advantage over superalloys.

Low-Alloy High-Strength Steel for Boiler Tubes (LowC-9Cr-2Mo)

1976 ◽  
Vol 98 (2) ◽  
pp. 173-178 ◽  
Author(s):  
T. Yukitoshi ◽  
K. Nishida ◽  
T. Oda ◽  
T. Daikoku
Keyword(s):  
High Temperature ◽  
High Strength Steel ◽  
Austenitic Stainless Steels ◽  
High Strength ◽  
Strengthening Mechanism ◽  
Steel Tube ◽  
High Temperature Strength ◽  
Low Alloy Steels ◽  
Service Test ◽  
Alloy Steels

High-strength steel tube HCM9M (LowC-9Cr-2Mo) steel, which shows the intermediate high-temperature strength between austenitic stainless steels and commercial low-alloy steels, has been developed. It has superior weldability, workability and oxidation resistivity. At present HCM9M tubes have been in-service test as reheater and superheater tubing at the 165,000 kW boiler in Japan without trouble. This report deals with the practical properties of HCM9M steel, service test experience and high temperature strengthening mechanism of the steel from morphological viewpoint of carbide.

Mechanical Properties and Microstructure of the Newly Developed Steel (Low C 18Cr-11Ni-3Cu-Mo-Nb-B-N) After Aging Treatment

2020 ◽  
Author(s):  
Nao Otaki ◽  
Tomoaki Hamaguchi ◽  
Takahiro Osuki ◽  
Yuhei Suzuki ◽  
Masaki Ueyama ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Vickers Hardness ◽  
Elevated Temperatures ◽  
Rupture Strength ◽  
Aging Treatment ◽  
High Strength ◽  
High Temperature Strength ◽  
Short Term ◽  
Rich Phase

Abstract In petroleum refinery plants, materials with high sensitization resistance are required. 347AP has particularly been developed for such applications and shows good sensitization resistance owing to its low C content. However, further improvement in high temperature strength is required for high temperature operations in complex refineries, such as delayed cokers. Recently, a new austenitic stainless steel (low C 18Cr-11Ni-3Cu-Mo-Nb-B-N, UNS No. S34752) with high sensitization resistance and high strength at elevated temperatures has been developed. In this study, the mechanical properties and microstructures of several aged specimens will be reported. By conducting several aging heat treatments in the range of 550–750 °C for 300–10,000 h on the developed steel, it was revealed that there were only few coarse precipitates that assumed sigma phase even after aging at 750 °C for 10,000 h. This indicates that the newly developed steel has superior phase stability. The developed steel drastically increased its Vickers hardness by short-term aging treatments. Through transmission electron microscopy observations, the fine precipitates of Cu-rich phase were observed dispersedly in the ruptured specimen. Therefore, the increase in Vickers hardness in short-term aging is possibly owing to the dispersed precipitation of Cu-rich phase. There was further increase in Vickers hardness owing to Z phase precipitation; however, the increment was smaller than that caused by Cu-rich phase. The newly developed alloy demonstrated excellent creep rupture strength even in the long-term tests of approximately 30,000 h, which is attributed to these precipitates.

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