Control of interfacial reactions and strength of the SiC/SiC joints brazed with newly-developed Co-based brazing alloy

2007 ◽  
Vol 22 (10) ◽  
pp. 2727-2736 ◽  
Author(s):  
Hua-Ping Xiong ◽  
Wei Mao ◽  
Yong-Hui Xie ◽  
Bo Chen ◽  
Wan-Lin Guo ◽  
...  
Keyword(s):  
High Temperature ◽  
Reaction Layer ◽  
Joint Strength ◽  
Room Temperature ◽  
Temperature Stability ◽  
High Temperature Strength ◽  
Bend Strength ◽  
High Temperature Stability ◽  
The Matrix ◽  
Point Bend

Co-based brazing alloy CoFeNi(Si, B)CrTi was designed for SiC joining. The periodic banded reaction structure that existed at the interface between SiC and the traditional Ni-based or Co-based braze has been eliminated by the new brazing alloy. The maximum room-temperature four-point bend strength of 161 MPa was achieved for SiC/SiC joint under the optimum brazing condition of brazing filler thickness of 120 μm, brazing temperature of 1150 °C, and brazing time of 10 min. The corresponding reaction layer of the SiC/SiC joint is composed of multilayer silicides and TiC band, and many small TiC particles are scattered throughout the matrix of the central part of the joint. The joints thus exhibit stable high-temperature strength. It is believed that the formation of TiC in the joint contributes not only to the elimination of the periodic banded reaction structure, but also to the high joint strength and the high-temperature stability.

High Temperature Stability of MGCs Gas Turbine Components in Air and Combustion Gas Flow Environments

2004 ◽  
Author(s):  
Narihito Nakagawa ◽  
Hideki Ohtsubo ◽  
Kohji Shibata ◽  
Atsuyuki Mitani ◽  
Kazutoshi Shimizu ◽  
...  
Keyword(s):  
High Temperature ◽  
Gas Turbine ◽  
Gas Flow ◽  
Temperature Stability ◽  
High Temperature Strength ◽  
High Temperature Stability ◽  
Combustion Gas ◽  
Air Atmosphere ◽  
Low Nox Emission ◽  
Very High

Melt growth composites (MGCs) have a unique microstructure, in which continuous networks of single-crystal phases interpenetrate without grain boundaries. Therefore, the MGCs have excellent high-temperature strength characteristics, creep resistance, oxidation resistance and thermal stability in an air atmosphere at very high temperature. To achieve ultra-high thermal efficiency and low NOx emission for gas turbine systems, non-cooled turbine nozzle vanes and heat shield panels of combustor liners has been fabricated on an experimental basis. These components are thermally stable after heat treatment at 1700°C for 1000 hours in an air atmosphere. In addition, we have just started the exposure tests to evaluate the influence of combustion gas flow environment on MGCs.

scholarly journals Room-temperature quantum cascade superluminescent light emitters with wide bandwidth and high temperature stability

2018 ◽  
Vol 26 (11) ◽  
pp. 13730 ◽  
Author(s):  
Chuncai Hou ◽  
Jialin Sun ◽  
Jiqiang Ning ◽  
Jinchuan Zhang ◽  
Ning Zhuo ◽  
...  
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Temperature Stability ◽  
High Temperature Stability ◽  
Light Emitters ◽  
Wide Bandwidth ◽  
Quantum Cascade

Processing, mechanical properties and oxidation behavior of TaC and HfC composites containing 15 vol% TaSi2 or MoSi2

2009 ◽  
Vol 24 (6) ◽  
pp. 2056-2065 ◽  
Author(s):  
Diletta Sciti ◽  
Laura Silvestroni ◽  
Stefano Guicciardi ◽  
Daniele Dalle Fabbriche ◽  
Alida Bellosi
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
High Temperature ◽  
Mechanical Strength ◽  
Hot Pressing ◽  
Room Temperature ◽  
Oxidation Behavior ◽  
Temperature Stability ◽  
High Temperature Stability ◽  
Better Than

Fully dense HfC and TaC-based composites containing 15 vol% TaSi2 or MoSi2 were produced by hot pressing at 1750–1900 °C. TaSi2 enhanced the sinterability of the composites and nearly fully dense materials were obtained at lower temperatures than in the case of MoSi2-containing ones. The TaC-based composites performed better than HfC composites at room temperature, showing values of mechanical strength up to 900 MPa and a fracture toughness of 4.7 MPa·m1/2. However, preliminary oxidation tests carried out in air at 1600 °C revealed that HfC-based composites have a superior high temperature stability compared to TaC-based materials.

HIGH TEMPERATURE STABILITY OF OPTICAL PROPERTIES OF InAs QUANTUM DOTS REALIZED BY CONTROLLING OF QUANTUM DOTS ELECTRONIC SPECTRUM

2007 ◽  
Vol 06 (03n04) ◽  
pp. 283-286 ◽  
Author(s):  
N. V. KRYZHANOVSKAYA ◽  
A. G. GLADYSHEV ◽  
S. A. BLOKHIN ◽  
A. P. VASIL'EV ◽  
E. S. SEMENOVA ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Optical Properties ◽  
High Temperature ◽  
Room Temperature ◽  
Temperature Stability ◽  
High Energy ◽  
Energy Separation ◽  
High Temperature Stability ◽  
Carrier Distribution ◽  
Inas Quantum Dots

The optical properties of InAs /( Al ) GaAs quantum dots (QDs) overgrowth by thin AlAs / InAlAs layers are studied as a function of temperature from 10 to 500 K. The QDs emit at 1.27 μm at room temperature. It is shown that the QD energetic spectrum can be tuned by overgrowth of AlAs / InAlAs to provide high temperature stability of the QDs optical properties. Transport of carriers between neighboring QDs is absent, and the carrier distribution remains nonthermal up to room temperature. It is shown that suppression of the thermal escaping of the carriers from QDs is conditioned by high energy separation between ground and excited states, absence of wetting layer level, and increase of carrier localization energy in QDs in case of the Al 0.3 Ga 0.7 As matrix.

Fundamental Core Effects in Transition Metal High-Entropy Alloys: “High-Entropy” and “Sluggish Diffusion” Effects

2021 ◽  
Vol 29 ◽  
pp. 75-93
Author(s):  
Abhishek Mehta ◽  
Yong Ho Sohn
Keyword(s):  
High Temperature ◽  
Temperature Stability ◽  
High Temperature Strength ◽  
High Entropy Alloys ◽  
High Temperature Stability ◽  
High Entropy ◽  
Diffusion Effects ◽  
Initial Work ◽  
Entropy Effect ◽  
Sluggish Diffusion

High entropy alloys (HEAs) are equimolar multi-principal-element alloys (MPEAs) that are different from traditional solvent-based multicomponent alloys based on the concept of alloy design. Based on initial work by Yeh and co-workers, HEAs were postulated to exhibit four “core” effects: high entropy, sluggish diffusion, lattice distortion, and cocktail effect. Out of these four proposed core effects, “high entropy” and “sluggish diffusion” effects were most debated in the literature as these core effects directly affect the thermodynamic and kinetic understanding of HEAs. The initial work on HEAs by several researchers utilized these effects to indirectly support the experimentally observed “unique” properties, without independent investigation of these core effects. The presumed implications of these core effects resulted in justification or generalization of properties to all HEAs, e.g., all HEAs should exhibit high temperature stability based on high entropy effect, high temperature strength owing to limited grain growth, good diffusion barrier application due to sluggish diffusion kinetics, etc. However, many recent studies have challenged these core effects, and suggested that not all HEAs were observed to exhibit these core effects.

High Temperature Stability of MGC’s Gas Turbine Components in Combustion Gas Flow Environments

2005 ◽  
Author(s):  
Narihito Nakagawa ◽  
Hideki Ohtsubo ◽  
Kohji Shibata ◽  
Atsuyuki Mitani ◽  
Kazutoshi Shimizu ◽  
...  
Keyword(s):  
Thermal Stability ◽  
High Temperature ◽  
Gas Flow ◽  
Temperature Stability ◽  
High Temperature Strength ◽  
High Temperature Stability ◽  
Exposure Test ◽  
Excellent Thermal Stability ◽  
Combustion Gas ◽  
Flow Environment

Melt growth composites (MGCs) have a unique microstructure, in which continuous networks of single-crystal phases interpenetrate without grain boundaries. Therefore, the MGCs have excellent high-temperature strength characteristics, creep resistance, oxidation resistance and thermal stability in an air atmosphere at very high temperature. In order to investigate the recession behavior of MGCs in combustion gas flow environment, we have just started the exposure tests to evaluate the influence of combustion gas flow environment on MGCs. The MGCs have about 95% of the initial flexural strengths after the exposure test for 10 hours at T = 1500 °C, P = 0.1–0.3 MPa, V = 150–250 m/s, PH2O = 15–45 kPa in the combustion gas flow environment. MGCs have excellent thermal stability and water vapor resistance in comparison with conventional ceramic materials such as Si3N4 and Al2O3 under the high temperature combustion gas flow environment.

Influence of Interfacial Characteristics on the Mechanical Properties of Continuous Fiber Reinforced Nial Composites

1992 ◽  
Vol 273 ◽  
Author(s):  
Randy R. Bowman
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Thermal Cycling ◽  
Oxidation Resistance ◽  
Cyclic Oxidation ◽  
Room Temperature ◽  
Matrix Cracking ◽  
High Temperature Strength ◽  
Interfacial Bond ◽  
The Matrix

ABSTRACTAs part of a study to assess NiAl-based composites as potential high-temperature structural materials, the mechanical properties of polycrystalline NiAl reinforced with 30 vol.% continuous single crystal Al2O3 fibers were investigated. Composites were fabricated with either a strong or weak bond between the NiAl matrix and Al2O3 fibers. The effect of interfacial bond strength on bending and tensile properties, thermal cycling response, and cyclic oxidation resistance was examined. Weakly-bonded fibers increased room-temperature toughness of the composite over that of the matrix material but provided no strengthening at high temperatures. With effective load transfer, either by the presence of a strong interfacial bond or by remotely applied clamping loads, Al2O3 fibers increased the high-temperature strength of NiAl but reduced the strain to failure of the composite compared to the monolithic material. Thermal cycling of the weakly-bonded material had no adverse effect on the mechanical properties of the composite. Conversely, because of the thermal expansion mismatch between the matrix and fibers, the presence of a strong interfacial bond generated residual stresses in the composite that lead to matrix cracking. Although undesirable under thermal cycling conditions, a strong interfacial bond was a requirement for achieving good cyclic oxidation resistance in the composite. In addition to the interfacial characterization, compression creep and room temperature fatigue tests were conducted on weakly-bonded NiAl/Al2O3 composites to further evaluate the potential of this system. These results demonstrated that the use of A12O3 fibers was successful in improving both creep and fatigue resistance.

scholarly journals Effects of Processing and Prolonged High Temperature Exposure on the Microstructure of Nb-1Zr-C Sheet

1993 ◽  
Vol 322 ◽  
Author(s):  
Mehmet Uz ◽  
R. H. Titran
Keyword(s):  
High Temperature ◽  
Prolonged Exposure ◽  
Temperature Stability ◽  
High Temperature Stability ◽  
Creep Properties ◽  
High Temperature Process ◽  
Processing History ◽  
The Matrix ◽  
Temperature Exposure ◽  
Complete Transformation

AbstractHigh temperature stability of the microstructure of Nb-lZr sheet containing 0.1 and 0.06 wt.%C was studied as affected by processing and prolonged 1350-K exposure with and without applied stress. Sheets were fabricated by cold rolling bars that were single-, double- or triple-extruded at 1900 K. Creep samples were double-annealed (1 h @ 1755 K + 2 h @ 1475 K) prior to testing at 1350 K for 10,000 - 34,500 h. The microstructures of the as-cast, extruded, rolled, DA and crept samples were characterized using various metallographic and analytical methods. The precipitates were rather coarse Nb2C initially, but transformed to finer (≤1 µm) carbides of (Zr,Nb)C with each subsequent high temperature process. The grain size, and the relative amount and morphology of (Zr,Nb)C were found to be affected by the number of extrusions and to some extent by C-content. However, the microstructures of all the crept samples were similar with (Zr,Nb)C distributed throughout the matrix indicating that prolonged exposure to 1350 K gave rise to complete transformation of Nb2 C to (Zr,Nb)C regardless of the processing history. These and other observations are presented with the emphasis on the correlation between processing, microstructure and creep properties.

Mechanical Properties of Dispersion-Hardened P/M Al-Mn-Cu-Mg-Zn Alloys at Elevated Temperature

2006 ◽  
Vol 519-521 ◽  
pp. 419-424
Author(s):  
Hiroki Adachi ◽  
Kozo Osamura ◽  
Jun Kusui
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Intermetallic Phase ◽  
Peak Level ◽  
Rietveld Analysis ◽  
Intermetallic Phases ◽  
Age Hardening ◽  
High Temperature Strength ◽  
The Matrix ◽  
Zn Alloys

In order to improve the high-temperature strength of an Al-Cu-Mg alloy, Mn was added at supersaturation to form a high-density dispersion of an intermetallic phase. In the P/M Al-3.6Mn- 6.4Cu-3.6Zn-1.7Mg alloy (mass%), rod-like Al-Mn-Cu-Zn quaternary intermetallic phases (Q phase) several hundred nanometers in length were dispersed in the matrix. The chemical composition of the Q phase was determined by TEM/EDX to be 78.8Al-12Mn-8Cu-1.2Zn (at%). The crystal system, space group, and lattice parameters of the unit cell were identified to be orthorhombic, Cmcm and a = 0.76, b = 2.11, c = 1.25 nm, respectively, by Rietveld analysis. Since the matrix of the alloy obtained was of the Al-Cu-Mg-(Zn) system, age-hardening occurred by formation of a GPB zone at room temperature and 448 K. At the peak level of age-hardening at room temperature, the tensile strength at room temperature was 704 MPa, and the elongations were 8.0%. The high temperature strengths at 523 and 573 K were 319 and 141 MPa, respectively, and the elongations were 17 and 34%, respectively.

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