The Effect of Strain Rate on the Yield Behavior of Iron-Based Lro Alloys at Elevated Temperatures

1986 ◽  
Vol 81 ◽  
Author(s):  
H. T. Lin ◽  
R. C. Wilcox ◽  
B. A. Chin
Keyword(s):  
Yield Strength ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Elevated Temperatures ◽  
Positive Temperature ◽  
Yield Behavior ◽  
Sem And Tem ◽  
Diffusion Controlled ◽  
Iron Based ◽  
Increasing Temperature

AbstractThe sensitivity of iron-based LRO alloys to strain rate at elevated temperatures was investigated. The tensile results indicate that the iron-based LRO alloys exhibit a positive temperature dependence of yield behavior, but are insensitive to variations in strain rate between 10-5 and 100 sec-1. These observations, along with SEM and TEM results, suggest that previous proposed diffusion-controlled mechanisms are not responsible for the increase in yield strength with increasing temperature.

scholarly journals The Effects of Temperature on the Leaching Behavior of Cement Waste Forms - The Cement/Sodium Sulfate System

1989 ◽  
Vol 176 ◽  
Author(s):  
Mark Fuhrmann ◽  
Richard Pietrzak ◽  
John Heiser ◽  
Eena-Mai Franz ◽  
Peter Colombo
Keyword(s):  
Sodium Sulfate ◽  
Elevated Temperatures ◽  
Effective Diffusion ◽  
Finite Cylinder ◽  
Kcal Mole ◽  
Experimental Conditions ◽  
Waste Forms ◽  
Diffusion Controlled ◽  
Increasing Temperature ◽  
Relationship Of

ABSTRACTThe leaching mechanisms of simulated low-level radioactive waste forms are being determined as support for development of an accelerated leach test. Two approaches are being used: (1) comparison of leaching data with results of a model that describes diffusion from a finite cylinder, and (2) observation of the leaching process at temperatures between 20°C and 65°C. To provide results that can be used for modeling, leaching at elevated temperatures must change neither the leaching mechanism nor the structural controls of leaching such as the porosity. Releases of 137Cs, 85Sr, calcium, sodium and potassium from portland cement containing sodium sulfate, as a simulated evaporator sludge, have been determined under a variety of experimental conditions. Data from the leach tests were compared to model results for diffusion from the finite cylinder. While most leaching appears to be diffusion controlled, notable exceptions occur. For all samples, activation energies ranging between 6 and 11 Kcal/mole have been calculated from the relationship of the effective diffusion coefficient to increasing temperature, close to the expected value of 5 Kcal/mole for diffusion.

The Effect of Strain Rate and Temperature on Yielding in Steels

1972 ◽  
Vol 94 (1) ◽  
pp. 207-212 ◽  
Author(s):  
D. P. Kendall
Keyword(s):  
Yield Strength ◽  
Mild Steel ◽  
Strain Rate ◽  
Maraging Steel ◽  
Elastic Strain ◽  
Constant Strain Rate ◽  
Rate Sensitivity ◽  
Strain Rates ◽  
Aging Effects ◽  
Increasing Temperature

The effect of elastic strain rates ranging from 10−14 to 10 sec−1 and temperatures ranging from 200 K (−100 F) to 590 K (600 F) on the yield strength of several steels is reported. The steels utilized are a 1018 mild steel, 4340 steel, H-11 tool steel, and 300 grade maraging steel. The results are interpreted in terms of the Cottrell-Bilby yielding model based on release of dislocations from locking carbon atmospheres. The results for all of the materials except the maraging steel are consistent with this model if it is modified to account for relocking of dislocations by migration of carbon atoms. The maraging steel shows a constant strain rate sensitivity at a constant temperature, over the range of strain rates investigated. This rate sensitivity decreases with increasing temperature and at 590 K (600 F) a decreasing strength with increasing strain rate is found. This is attributed to stress aging effects.

Temperature Dependence of Impact Ionization Coefficients in 4H-SiC

2014 ◽  
Vol 778-780 ◽  
pp. 461-466 ◽  
Author(s):  
Hiroki Niwa ◽  
Jun Suda ◽  
Tsunenobu Kimoto
Keyword(s):  
Temperature Dependence ◽  
Temperature Coefficient ◽  
Breakdown Voltage ◽  
Elevated Temperatures ◽  
Phonon Scattering ◽  
Impact Ionization ◽  
Negative Temperature ◽  
Positive Temperature Coefficient ◽  
Positive Temperature ◽  
Ionization Coefficients

Impact ionization coefficients of 4H-SiC were measured at room temperature and at elevated temperatures up to 200°C. Photomultiplication measurement was done in two complementary photodiodes to measure the multiplication factors of holes (Mp) and electrons (Mn), and ionization coefficients were extracted. Calculated breakdown voltage using the obtained ionization coefficients showed good agreement with the measured values in this study, and also in other reported PiN diodes and MOSFETs. In high-temperature measurement, breakdown voltage exhibited a positive temperature coefficient and multiplication factors showed a negative temperature coefficient. Therefore, extracted ionization coefficient has decreased which can be explained by the increase of phonon scattering. The calculated temperature dependence of breakdown voltage agreed well with the measured values not only for the diodes in this study, but also in PiN diode in other literature.

On the Effect of Strain Rate and Temperature on the Yield Strength Anomaly in L21-structured Fe2AlMn

2008 ◽  
Vol 1128 ◽  
Author(s):  
Markus W. Wittmann ◽  
Janelle M. Chang ◽  
Yifeng Liao ◽  
Ian Baker
Keyword(s):  
Yield Strength ◽  
Strain Rate ◽  
Single Crystals ◽  
Yield Stress ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Temperature Range ◽  
Effects Of Temperature ◽  
Increasing Temperature

AbstractThe effects of strain rate and temperature on the yield strength of near-stoichiometric Fe2AlMn single crystals were investigated. In the temperature range 600-800K the yield stress increased with increasing temperature, a response commonly referred to as a yield strength anomaly. No strain rate sensitivity was observed below 750K, but at higher temperatures the yield stress increased with increasing strain rate. Possible mechanisms to explaining the effects of temperature and strain rate are discussed.

Parameter Representation of Low-Temperature Yield Behavior of Body-Centered Cubic Transition Metals

1966 ◽  
Vol 88 (2) ◽  
pp. 518-524 ◽  
Author(s):  
P. E. Bennett ◽  
G. M. Sinclair
Keyword(s):  
Low Temperature ◽  
Transition Metals ◽  
Brittle Fracture ◽  
Yield Strength ◽  
Strain Rate ◽  
Body Centered Cubic ◽  
Yield Behavior ◽  
Bcc Metals ◽  
State Of Stress ◽  
Iron Chromium

In the low-temperature range, the engineering yield strength of polycrystalline bcc metals can change by a factor of 10 or more with serious consequences appearing in the form of catastrophic brittle fracture. Engineering variables known to have an important effect on the yield behavior are state of stress, temperature, loading or strain rate, composition, and microstructure. For iron, chromium, molybdenum, and tungsten, it is shown that yield behavior can be represented by a single-valued relation between two dimensionless parameters.

scholarly journals Violation of the T−1 Relationship in the Lattice Thermal Conductivity of Mg3Sb2 with Locally Asymmetric Vibrations

Research ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Yifan Zhu ◽  
Yi Xia ◽  
Yancheng Wang ◽  
Ye Sheng ◽  
Jiong Yang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Temperature Dependence ◽  
Lattice Thermal Conductivity ◽  
Elevated Temperatures ◽  
Low Frequency ◽  
Strong Temperature Dependence ◽  
Depth Analysis ◽  
Force Profile ◽  
Phonon Renormalization ◽  
Increasing Temperature

Most crystalline materials follow the guidelines of T−1 temperature-dependent lattice thermal conductivity (κL) at elevated temperatures. Here, we observe a weak temperature dependence of κL in Mg3Sb2, T−0.48 from theory and T−0.57 from measurements, based on a comprehensive study combining ab initio molecular dynamics calculations and experimental measurements on single crystal Mg3Sb2. These results can be understood in terms of the so-called “phonon renormalization” effects due to the strong temperature dependence of the interatomic force constants (IFCs). The increasing temperature leads to the frequency upshifting for those low-frequency phonons dominating heat transport, and more importantly, the phonon-phonon interactions are weakened. In-depth analysis reveals that the phenomenon is closely related to the temperature-induced asymmetric movements of Mg atoms within MgSb4 tetrahedron. With increasing temperature, these Mg atoms tend to locate at the areas with relatively low force in the force profile, leading to reduced effective 3rd-order IFCs. The locally asymmetrical atomic movements at elevated temperatures can be further treated as an indicator of temperature-induced variations of IFCs and thus relatively strong phonon renormalization. The present work sheds light on the fundamental origins of anomalous temperature dependence of κL in thermoelectrics.

Effect of Strain Rate on the Plastic Behaviour of Ll2 Compounds Based on Ni3Al

1988 ◽  
Vol 133 ◽  
Author(s):  
Seiji Miura ◽  
Shouichi Ochiai ◽  
Yoshihiro Oya ◽  
Yoshinao Mishima ◽  
Tomoo Suzuki
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Rate Sensitivity ◽  
Grain Boundary Sliding ◽  
Rate Dependence ◽  
Strain Rate Dependence ◽  
Positive Temperature ◽  
Fine Grain ◽  
Positive Temperature Dependence

ABSTRACTIn both single and polycrystalline Ni3Al, no strain rate dependence of 0.2% flow stress is observed in a temperature range where anomalous positive temperature dependence of strength is exhibited. A distinct strain rate dependence is observed, however, in single crystals when the test temperature is raised beyond the peak in flow stress. It is shown that (111) type slip involving diffusional process is responsible for the strain rate sensitivity at near [001] orientation, while (001) type slip which is governed by the Peierls mechanism at orientations away from [001]. In polycrystalline compound with a fine grain size an apparent loss of the positive temperature dependence of strength is observed at a slower strain rate due to grain boundary sliding.

The Effect of Prestrain on Deformation of Ni3Al Single Crystals

1988 ◽  
Vol 133 ◽  
Author(s):  
W. E. Dowling ◽  
R. Gibala
Keyword(s):  
Flow Stress ◽  
Plastic Strain ◽  
Yield Strength ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Negative Temperature ◽  
Dislocation Dynamics ◽  
Positive Temperature ◽  
Initial Flow ◽  
Bcc Metals

ABSTRACTPrestrain of bcc metals at temperatures T>0.2Tm decreases the flow stress at lower temperatures (T<O.15Tm) where the yield strength has a large negative temperature dependence. This investigation has examined the influence of prestrain on the flow stress of Ni3A1, for which the yield strength has a large positive temperature dependence above 25°C. Nickel-rich Ni3Al single crystals with axial orientations near <001> or <123> were prestrained in compression up to 20% shear strain at -196°C and subsequently compression tested at 550°C. Specimens near the <123> axial orientation were also prestrained at 550°C and then tested at -196°C. The initial flow stress of samples prestrained at - 196°C and tested 550°C was reduced up to 50% compared to samples solely compression tested at 550°C. The magnitude of the reduced flow stress and its extent as a function of plastic strain were dependent upon the amount of prestrain and orientation. Prestraining at 550°C and subsequent testing at -196°C increased the flow stress by as much as 60% over samples solely tested at -196°C. Dislocation substructures obtained from selected samples coupled with arguments based on dislocation dynamics and obstacle strengthening are used to explain the results.

Tensile behaviour and damage characteristic of recycled aluminium alloys AA6061 undergoing finite strain deformation

2020 ◽  
pp. 095440622095034
Author(s):  
CS Ho ◽  
MK Mohd Nor
Keyword(s):  
Strain Rate ◽  
Aluminium Alloys ◽  
Elevated Temperatures ◽  
Microstructural Analysis ◽  
Optical Microscope ◽  
Uniaxial Tensile ◽  
Tensile Behaviour ◽  
Uniaxial Tensile Test ◽  
Increasing Temperature ◽  
Damage Characteristic

The effects of temperature and strain rate of hot-forged recycled aluminium alloys AA6061 are examined via uniaxial tensile test implementations in this paper. The tests are conducted at elevated temperatures of 100 °C, 200 °C and 300 °C, at two different strain rates of 10−4 s−1 and 10−3 s−1. The tensile behaviour and damage characteristic are analysed in terms of stress-strain curves and microstructural analysis, respectively. The microstructure and fracture surface of such materials are observed using Scanning Electron Microscope (SEM) and Optical Microscope (OM). The flow stress of recycled AA6061 increases with increasing strain rate and decreases with increasing temperature. ImageJ software is used to quantify void characteristics. It is observed that the quantity and size of the micro-voids are strain-rate sensitive. This is due to the growth and coalescence of the micro-voids. The OM analysis shows the gap between the grain boundaries becomes wider with the increasing temperature that affects the strength of the material. The outcome of this work gives valuable information before the appropriate applications, especially in automotive and aerospace fields, can be established. It can be agreed that there is still a need for improved recycling methods to fulfil the needs in the required applications, as shown by its primary resources. It is a massive challenge and an obvious drawback in such materials due to the degradation of material’s properties related to damage.

Mechanical Properties of a β Containing Ti-Al-Cr-Alloy at Ambient and Elevated Temperatures

1994 ◽  
Vol 364 ◽  
Author(s):  
W. R. Chen ◽  
J. Wang ◽  
B. Zhang ◽  
X. Wan ◽  
W. J. Chen
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Ambient Temperature ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Elevated Temperatures ◽  
High Tensile Strength ◽  
Tial Alloys ◽  
Β Phase ◽  
Very High

AbstractThe mechanical properties of a β-containing Ti-Al-Cr alloy were investigated at ambient and elevated temperatures. The results show that the Ti-Al-Cr alloy containing the β phase has a very high tensile strength but a poor ductility at ambient temperature, and that higher ductility is obtained at high temperatures. The temperature dependence of mechanical properties is found to be sensitive to the strain rate during the test. Fractography shows that the fracture mode changes from fully brittle to ductile-brittle mixture with the increased temperature. All the results suggest that the triple-phased TiAl alloys (α2+β+γ) may have the combined mechanical properties of the dual-phased T13Al ((α2+β) and dual-phased TiAl (α2+γ) alloys.

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