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.

Electrical and Magnetic Properties of CuEu2W2O10 and Cu3Eu2W4O18

2012 ◽  
Vol 194 ◽  
pp. 104-107 ◽  
Author(s):  
Piotr Urbanowicz ◽  
Elzbieta Tomaszewicz ◽  
Tadeusz Groń ◽  
Henryk Duda ◽  
Slawomir Mazur ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Activation Energy ◽  
Magnetic Properties ◽  
Room Temperature ◽  
Linear Temperature Dependence ◽  
Linear Temperature ◽  
Weak Response ◽  
Thermally Activated ◽  
Electrical And Magnetic Properties ◽  
P Type

Magnetic susceptibility measurements showed both a weak response to magnetic field and a lack of the Curie-Weiss region for CuEu2W2O10and Cu3Eu2W4O18tungstates characteristic for the multiplet widths comparable to thermal energy. Magnetization measurements displayed the linear temperature dependence with the lower magnetic moment for Cu3Eu2W4O18in comparison with CuEu2W2O10, indicating that the effect of the electric charges associated with the surrounding ligands can change the multiplet width of individual states. It is affecting the electrical properties of examined tungstates which reveal the insulating state and low relative permittivity εr ~ 29 in case of CuEu2W2O10and the thermally activated p-type electrical conduction for Cu3Eu2W4O18with the activation energy of 1.11 eV and the large value of εr ~ 217 above the room temperature.

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.

THE EFFECT OF STRESS RATE AND TEMPERATURE ON THE STRENGTH OF BASALT AND GRANITE

Geophysics ◽  
1968 ◽  
Vol 33 (3) ◽  
pp. 501-510 ◽  
Author(s):  
A. Kumar
Keyword(s):  
Activation Energy ◽  
Dynamic Modulus ◽  
Room Temperature ◽  
Liquid Nitrogen Temperature ◽  
Stress Rate ◽  
Combined Effects ◽  
Rock Fracturing ◽  
Pulse Technique ◽  
Thermally Activated ◽  
Insight Into

The ultimate strengths of basalt and granite were measured over a range of stress rates from 2×10 to [Formula: see text] psi per second. A comparison of basalt and granite showed that, although their static strengths were close, their dynamic strengths were different. The static strengths of basalt and granite were 27.5 and 29 kpsi, respectively, at the stress rate of 2×10 psi per second while their strengths at the stress rate of [Formula: see text] psi per second were 59 and 70 kpsi, respectively. In order to obtain an insight into the basic mechanisms of rock fracturing, the combined effects of stress rate and temperature were studied. The strength of basalt was increased from 27.5 kpsi at room temperature to 45 kpsi at liquid nitrogen temperature at the stress rate of 2×10 psi per second. The mechanisms of fracturing were thermally activated. The activation energy for basalt at 50 kpsi equalled 450 calories per mole. The dynamic modulus of basalt measured by the pulse technique was [Formula: see text] psi. The value of the dynamic modulus obtained at a stress rate of [Formula: see text] psi per second was [Formula: see text] psi.

scholarly journals The Effect of Pre-Annealing on the Evolution of the Microstructure and Mechanical Behavior of Aluminum Processed by a Novel SPD Method

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2361 ◽  
Author(s):  
Alexander P. Zhilyaev ◽  
Mario J. Torres ◽  
Homero D. Cadena ◽  
Sandra L. Rodriguez ◽  
Jessica Calvo ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Grain Size ◽  
High Temperature ◽  
Room Temperature ◽  
Pure Aluminum ◽  
Continuous Process ◽  
Tensile Tests ◽  
New Method ◽  
Slow Cooling

A novel continuous process of severe plastic deformation (SPD) named continuous close die forging (CCDF) is presented. The CCDF process combines all favorite advances of multidirectional forging and other SPD methods, and it can be easily scaled up for industrial use. Keeping constant both the cross section and the length of the sample, the new method promotes a refinement of the microstructure. The grain refinement and mechanical properties of commercially pure aluminum (AA1050) were studied as a function of the number of CCDF repetitive passes and the previous conditioning heat treatment. In particular, two different pre-annealing treatments were applied. The first one consisted of a reheating to 623 K (350 °C) for 1 h aimed at eliminating the effect of the deformation applied during the bar extrusion. The second pre-annealing consisted on a reheating to 903 K (630 °C) for 48 h plus cooling down to 573 K (300 °C) at 66 K/h. At this latter temperature, the material remained for 3 h prior to a final cooling to room temperature within the furnace, i.e., slow cooling rate. This treatment aimed at increasing the elongation and formability of the material. No visible cracking was detected in the workpiece of AA1050 processed up to 16 passes at room temperature after the first conditioning heat treatment, and 24 passes were able to be applied when the material was subjected to the second heat treatment. After processing through 16 passes for the low temperature pre-annealed samples, the microstructure was refined down to a mean grain size of 0.82 µm and the grain size was further reduced to 0.72 µm after 24 passes, applied after the high temperature heat treatment. Tensile tests showed the best mechanical properties after the high temperature pre-annealing and 24 passes of the novel CCDF method. A yield strength and ultimate tensile strength of 180 and 226 MPa, respectively, were obtained. Elongation to fracture was 18%. The microstructure and grain boundary nature are discussed in relation to the mechanical properties attained by the current ultrafine-grained (UFG) AA1050 processed by this new method.

Annealing of Deformed Materials Developed by Continuous/Discontinuous Dynamic Recrystallization

2007 ◽  
Vol 550 ◽  
pp. 327-332 ◽  
Author(s):  
Taku Sakai ◽  
Hiromi Miura
Keyword(s):  
Dynamic Recrystallization ◽  
Room Temperature ◽  
Static Recrystallization ◽  
Pure Copper ◽  
Large Strains ◽  
Static Recovery ◽  
Fine Grained ◽  
Texture Change ◽  
Characteristic Nature ◽  
Fine Grained Structure

Annealing behaviour was studied in deformed copper developed by continuous or discontinuous dynamic recrystallization (cDRX or dDRX). Pure copper was deformed to large strains by multi-directional forging at room temperature, resulting in an ultra-fine grained structure due to operation of cDRX. Subsequent annealing of such a fine-grained copper can be controlled mainly by grain growth accompanied with recovery and no texture change, that is continuous static recrystallization (cSRX). On the other hand, 4 kinds of static restoration processes operate during annealing of dDRXed copper, i.e. metadaynamic recovery and recystallization (mDRV and mDRX), and classical static recovery and recrystallization. The stable existence of mDRVed grains containing moderate dislocations leads to incomplete recrystallization even after a long period of annealing time. It is discussed how such various types of annealing processes, occurring in cDRXed or dDRXed matrices, can be connected with the characteristic nature of the deformed microstructures.

Mass spectrometric study of allyl radical, allyl bromide and 1,5-hexadiene interactions with oxides; Cobalt suboxide Co3O4

1979 ◽  
Vol 44 (7) ◽  
pp. 2009-2014 ◽  
Author(s):  
Jana Nováková ◽  
Zdeněk Dolejšek
Keyword(s):  
Room Temperature ◽  
Allyl Bromide ◽  
Catalytic Properties ◽  
Mass Spectrometric Study ◽  
Spectrometric Study ◽  
Flow Conditions ◽  
Allyl Radical ◽  
Knudsen Flow ◽  
Thermally Activated ◽  
Radical Interaction

Products of (a) allyl radical interaction with unheated Co3O4, (b) thermally activated 1,5-hexadiene or thermally activated allyl bromide with unheated Co3O4, (c) moderately heated Co3O4 with unheated 1,5-hexadiene or allyl bromide were studied under Knudsen flow conditions. Cobalt suboxide Co3O4, a typical catalyst of deep oxidations yielded acrolein in reaction with allyl radicals as early as at the room temperature of the catalyst. A similar acrolein formation was also observed in the allyl radical interaction with other oxides exhibiting different catalytic properties. It appears that acrolein is in general the primary product of the allyl radical interaction with the oxides. The results are discussed and compared with previous data obtained with MoO3.

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.

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