High temperature creep of SiC densified using a transient liquid phase

1991 ◽  
Vol 6 (9) ◽  
pp. 1945-1949 ◽  
Author(s):  
Zuei C. Jou ◽  
Anil V. Virkar ◽  
Raymond A. Cutler
Keyword(s):  
Activation Energy ◽  
Silicon Carbide ◽  
Liquid Phase ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Transient Liquid Phase ◽  
High Strength ◽  
High Temperature Creep ◽  
Fine Grained ◽  
Thermally Activated

Silicon carbide-based ceramics can be rapidly densified above approximately 1850 °C due to a transient liquid phase resulting from the reaction between alumina and aluminum oxycarbides. The resulting ceramics are fine-grained, dense, and exhibit high strength at room temperature. SiC hot pressed at 1875 °C for 10 min in Ar was subjected to creep deformation in bending at elevated temperatures between 1500 and 1650 °C in Ar. Creep was thermally activated with an activation energy of 743 kJ/mol. Creep rates at 1575 °C were between 10−9/s and 10−7/s at an applied stress between 38 and 200 MPa, respectively, resulting in a stress exponent of ≍1.7.

On the use of Ozawa/Flynn/Wall method to determine aging activation energy for elastomers

2021 ◽  
pp. 009524432110203
Author(s):  
Sudhir Bafna
Keyword(s):  
Mechanical Properties ◽  
Activation Energy ◽  
Weight Loss ◽  
Oxygen Consumption ◽  
Dwell Time ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Degradation Mechanism ◽  
Kinetics Of ◽  
Wall Method

It is often necessary to assess the effect of aging at room temperature over years/decades for hardware containing elastomeric components such as oring seals or shock isolators. In order to determine this effect, accelerated oven aging at elevated temperatures is pursued. When doing so, it is vital that the degradation mechanism still be representative of that prevalent at room temperature. This places an upper limit on the elevated oven temperature, which in turn, increases the dwell time in the oven. As a result, the oven dwell time can run into months, if not years, something that is not realistically feasible due to resource/schedule constraints in industry. Measuring activation energy (Ea) of elastomer aging by test methods such as tensile strength or elongation, compression set, modulus, oxygen consumption, etc. is expensive and time consuming. Use of kinetics of weight loss by ThermoGravimetric Analysis (TGA) using the Ozawa/Flynn/Wall method per ASTM E1641 is an attractive option (especially due to the availability of commercial instrumentation with software to make the required measurements and calculations) and is widely used. There is no fundamental scientific reason why the kinetics of weight loss at elevated temperatures should correlate to the kinetics of loss of mechanical properties over years/decades at room temperature. Ea obtained by high temperature weight loss is almost always significantly higher than that obtained by measurements of mechanical properties or oxygen consumption over extended periods at much lower temperatures. In this paper, data on five different elastomer types (butyl, nitrile, EPDM, polychloroprene and fluorocarbon) are presented to prove that point. Thus, use of Ea determined by weight loss by TGA tends to give unrealistically high values, which in turn, will lead to incorrectly high predictions of storage life at room temperature.

Static Recovery Activation Energy of Pure Aluminum at Room Temperature

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Yeh An-Chou ◽  
Chuang Ho-Chieh ◽  
Kuo Chen-Ming
Keyword(s):  
Activation Energy ◽  
Room Temperature ◽  
Pure Aluminum ◽  
Pure Copper ◽  
Tensile Tests ◽  
Engineering Strain ◽  
Static Recovery ◽  
Thermally Activated ◽  
Recovered Strain ◽  
Dislocation Annihilation

Thermally activated energy, which varies linearly with static recovered strain, is calculated from static recovery experiments of pure aluminum initially plastically deformed by strain-rate-controlled tensile tests up to 10% engineering strain at room temperature. The activation energy at the initial static recovery is 20 kJ mol−1, which is much less than that of pure copper and attributed to the dislocation annihilation by glide or cross-slip as well as higher stacking fault energy. Once dislocation annihilation processes are exhausted, more energy is required for subgrains to form and then grow. Eventually the recovered strain is slowed down and gradually saturated.

The Crystallization of a-ZnTe

1975 ◽  
Vol 53 (22) ◽  
pp. 2481-2484 ◽  
Author(s):  
J. B. Webb ◽  
D. E. Brodie
Keyword(s):  
Activation Energy ◽  
Room Temperature ◽  
Crystallization Process ◽  
Amorphous Material ◽  
Amorphous State ◽  
Zinc Telluride ◽  
Thermally Activated ◽  
Maximum Time

The crystallization of amorphous zinc telluride (a-ZnTe) has been studied as a function of temperature in the range 350 K < T < 390 K. The crystallization process is thermally activated with an activation energy of 1.6 eV. The time for the onset of significant crystallization at room temperature for films of air-annealed a-ZnTe is found to be ~100 years. The study of the crystallization process is essential in order to determine the maximum time allowed for a measurement to be performed at a given temperature on a sample of amorphous material without significantly altering its amorphous state.

Evolution of Microstructure during Hot Deformation of the PM Molybdenum Alloy TZM

2007 ◽  
Vol 539-543 ◽  
pp. 2725-2730 ◽  
Author(s):  
T. Mrotzek ◽  
Andreas Hoffmann ◽  
U. Martin ◽  
H. Oettel
Keyword(s):  
Yield Strength ◽  
Hot Deformation ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
High Strength ◽  
Tensile Tests ◽  
Primary Recrystallization ◽  
Molybdenum Alloy ◽  
Texture Formation ◽  
Evolution Of Microstructure

The molybdenum alloy TZM (Mo-0.5wt%Ti-0.08wt%Zr) is a commonly used structural material for high temperature applications. For these purposes a high strength at elevated temperatures and also a sufficient ductility at room temperature are being aimed. Preceding investigations revealed the existence of subgrains in hot deformed TZM. It was observed that with proceeding primary recrystallization and therefore with disappearance of subgrains the yield strength drops almost to a level of pure molybdenum. It is being assumed that the existence of a dislocation substructure has a pronounced effect on the yield strength of TZM. The aim of the present study was to evaluate the subgrain and texture formation and also to estimate the dislocation arrangement within subgrains during hot deformation. Hence, TZM rods were rolled to different degrees of deformation at a temperature above 0.5 Tm. The microstructure of the initial material was fully recrystallized. Texture formation, misorientation distributions and subgrain sizes were analyzed by electron backscattering diffraction (EBSD). Mechanical properties were characterized by tensile tests at room temperature and up to 1200°C. It was revealed, that with increasing degree of deformation a distinct substructure forms and therefore yield strength rises. Consequently, the misorientation between adjacent subgrains increases, their size decreases and a <110> fibre texture develops. To estimate the influence of texture on strength of TZM the Taylor factors are calculated from EBSD data.

Effect of Stress Relaxation on Springback of Steel Sheet in Warm Forming

2016 ◽  
Vol 725 ◽  
pp. 671-676 ◽  
Author(s):  
Naoko Saito ◽  
Mitsugi Fukahori ◽  
Daisuke Hisano ◽  
Hiroshi Hamasaki ◽  
Fusahito Yoshida
Keyword(s):  
Stress Relaxation ◽  
High Strength Steel ◽  
Room Temperature ◽  
Steel Sheet ◽  
Elevated Temperatures ◽  
High Strength ◽  
Warm Forming ◽  
Sheet Metals ◽  
Stress Relaxation Behavior ◽  
Increasing Temperature

Springback of a high strength steel (HSS) sheet of 980 MPa grade was investigated at elevated temperatures ranging from room temperature to 973 K. From U-and V-bending experiments it was found that springback was decreased with increasing temperature at temperatures of above 573 K. Furthermore, springback was decreased with punch-holding time because of stress relaxation. In this work, the stress relaxation behavior of the steel was experimentally measured. By using an elasto-vicoplasticity model, the stress relaxation was described, and its effect on the springback of sheet metals in warm forming was discussed theoretically.

Process Development of Silicon-Silicon Carbide Hybrid Micro-Engine Structures

2001 ◽  
Vol 687 ◽  
Author(s):  
Dongwon Choi ◽  
Robert J. Shinavski ◽  
Wayne S. Steffier ◽  
Skip Hoyt ◽  
S.Mark Spearing
Keyword(s):  
Silicon Carbide ◽  
Residual Stresses ◽  
Elevated Temperatures ◽  
Process Development ◽  
High Stress ◽  
Development Program ◽  
High Strength ◽  
Operating Conditions ◽  
Source Power ◽  
Silicon Silicon

AbstractA MEMS-based gas turbine engine is being developed for use as a button-sized portable power generator or micro-aircraft propulsion source. Power densities expected for the micro- engine require high combustor exit temperatures (1300-1700K) and very high rotor peripheral speeds (300-600m/s). These harsh operating conditions induce high stress levels in the engine structure, and thus require refractory materials with high strength. Silicon carbide has been chosen as the most promising material for use in the near future due to its high strength and chemical inertness at elevated temperatures. However, techniques for microfabricating single- crystal silicon carbide to the level of high precision needed for the micro-engine are not currently available. To circumvent this limitation and to take advantage of the well-established precise silicon microfabrication technologies, silicon-silicon carbide (SiC) hybrid turbine structures are being developed using chemical vapor deposition of poly-SiC on silicon wafers and wafer bonding processes. Residual stress control of SiC coatings is of critical importance to all the silicon-silicon carbide hybrid structure fabrication steps since a high level of residual stresses causes wafer cracking during the planarization, as well as excessive wafer bow, which is detrimental to the subsequent planarization and bonding processes. The origins of the residual stresses in CVD SiC layers have been studied. SiC layers (as thick as 30µm) with low residual stresses (on the order of several tens of MPa) have been produced by controlling CVD process parameters such as temperature and gas ratio. Wafer-level SiC planarization has been accomplished by mechanical polishing using diamond grit and bonding processes are currently under development using interlayer materials such as silicon dioxide or poly-silicon. These process development efforts will be reviewed in the context of the overall micro-engine development program.

Influence of Nitride on Sinterability of the Composite of Lithium Aluminum Silicate and Silicon Carbide

2006 ◽  
Vol 317-318 ◽  
pp. 177-180 ◽  
Author(s):  
Mabito Iguchi ◽  
Motohiro Umezu ◽  
Masako Kataoka ◽  
Hiroaki Nakamura ◽  
Mamoru Ishii
Keyword(s):  
Silicon Carbide ◽  
Thermal Expansion ◽  
Melting Point ◽  
Liquid Phase ◽  
Room Temperature ◽  
Aluminum Silicate ◽  
Lithium Aluminum ◽  
Sintering Process ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

Ceramics with zero thermal expansion coefficients at room temperature (293K) were investigated. We found the thermal expansion coefficient was controlled by a compounding ratio of lithium aluminum silicate (LAS) and silicon carbide (SiC), which have negative and positive thermal expansion coefficients respectively. Although it was difficult to densify the composite of the LAS and SiC (LAS/SiC) in the sintering process, an addition of nitride improved the sinterability of the LAS/SiC. In order to examine the effect of the nitride additive, at first, the melting point of the LAS with silicon nitride (Si3N4) or aluminum nitride was measured by TG-DTA. The melting point of the LAS decreased with existence of nitride. It is believed that the densification of the LAS/SiC was promoted by the nitride, because the nitride causes the LAS/SiC to form a liquid phase, thereby decreasing the melting point. Next, the lattice constant of the LAS with Si3N4 was measured by XRD and it was verified that the a-axis was longer and the c-axis was shorter than those of the LAS without additive. It is supposed that this phenomenon is due to the substitution of nitrogen for oxygen in the LAS lattice, and the decrease of the melting point of the LAS with nitride seems to be influenced by this substitution of nitrogen.

scholarly journals STRAIN BEHAVIOUR OF ULTRA-HIGH-STRENGTH CONCRETE UNDER THE ELEVATED TEMPERATURE AND 0.25FCK LOADING

2016 ◽  
Author(s):  
Gyu Yong Kim ◽  
Young Wook Lee ◽  
Nenad Gucunski ◽  
Gyeong Cheol Choe ◽  
Min Ho Yoon
Keyword(s):  
Compressive Strength ◽  
High Temperature ◽  
High Strength Concrete ◽  
Loading Condition ◽  
Elevated Temperatures ◽  
High Strength ◽  
Total Strain ◽  
High Temperature Creep ◽  
Temperature Creep ◽  
Strain Behaviour

The high-temperature creep of Ultra-High-Strength Concrete (UHSC) has been investigated in this study. The purpose of this study is to evaluated total strain and high-temperature creep at elevated temperatures under loading condition of UHSC. To evaluate the strain behaviour of UHSC at elevated temperatures, ϕ100 mm × 200 mm cylindrical specimens of UHSC with compressive strengths of 80, 130 and 180 MPa concrete were heated to 700 °C at a rate of 1 °C/min. The total strain and high-temperature-creep were measured under the loading condition of 0.25 of the compressive strength at room temperature. As results, Total strain of UHSC increased showing shrinkage with increasing compressive strength. The high-temperature creep of UHSC increased with the temperature and higher level of compressive strength showed bigger high-temperature creep.

Transient Liquid Phase Bonding of High Strength Low Alloy Steel Coiled Tubing

2010 ◽  
Vol 442 ◽  
pp. 66-73 ◽  
Author(s):  
A. Javadzadeh ◽  
T.I. Khan
Keyword(s):  
Liquid Phase ◽  
Hsla Steel ◽  
Bonding Temperature ◽  
Transient Liquid Phase ◽  
High Strength ◽  
Oil And Gas Industry ◽  
Tube Steel ◽  
Joint Region ◽  
Coiled Tubing ◽  
Tlp Bonding

The oil and gas industry of Alberta, Canada use coiled tubing made from high strength low alloyed steel (HSLA) to extract oil from reservoirs deep beneath the earth’s surface. The repeated use of the coiled tubing in down-hole wells results in fatigue failure of the tube material. In order to repair the coiled tube, a section of tubing is fusion welded using tungsten inert gas welding onto the remaining tube steel. However, the fusion weld often fails within the weld region and therefore, alternative joining methods need to be explored to minimize detrimental changes at the joint region. In this study transient liquid phase (TLP) bonding is used with the aid of metal interlayers based on the Ag-Cu and Ni-P systems. These interlayers form a liquid at the melting point and the gradual diffusion of alloying elements into the joint and the diffusion of elements out of the joint region induces isothermal solidification whilst the joint is held at the bonding temperature. The TLP bonding behaviour of the HSLA steel as a function of bonding parameters was investigated and the quality of the joint region determined using metallurgical techniques (light and scanning electron microscopy, energy dispersive spectroscopy) and mechanical testing.

SPECIAL GENCO

Alloy Digest ◽  
1965 ◽  
Vol 14 (2) ◽  
Keyword(s):  
Stainless Steel ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
High Strength ◽  
Heat Treating ◽  
Steel Company ◽  
Temperature Range ◽  
Temperature Performance ◽  
Corrosion And Oxidation ◽  
Chromium Stainless Steel

Abstract Special Genco is a hardenable 12% chromium stainless steel developed for applications requiring superior strength to Type 403 stainless steel at elevated temperatures. This grade retains high strength and exhibits excellent ductility over the temperature range from room temperature to 1200 F. Special Genco provides excellent resistance to corrosion and oxidation within this temperature range. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness and creep. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SS-165. Producer or source: Latrobe Steel Company.

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